EP0193546B1 - Digital decompressemeter with variable perfusions and method for effecting it - Google Patents

Abstract

The decompressemeter is intended to take into account the excercise of the diver and/or the temperature of the ambient medium to determine more accurately the optimum decompression program. Thus, the determination process in real time of the decompression program of a diver or a hyperbar worker comprises essentially: - measuring during exposure the time and the ambient pressure, - measuring and/or determining also during exposure at least one of the following additional parameters: 1) perfusion of one or a plurality of tissues, 2) heart flowrate, 3) pulmonar ventilation, 4) oxygen consumption, 5) heart pulse rate, 6) ambient temperature, - and deducing an estimation of the saturation stages of a diver and the appropriate decompression program.

Description

The invention relates to a method for determining the minimum non-pathological decompression program for a person (diver, hyperbaric worker, aviator, cosmonaut, etc.) who has stayed and breathed a gas mixture containing one or more gases which cannot be metabolized at ambient pressures. greater than that of the "surface" that it ultimately wants to reach, as well as an automatic device for determining and indicating said program and related parameters applying the said method as well as a diving assembly incorporating the said device.

The need for a decompression program stems from the fact that, during the pressure stay, the non-metabolizable gases have dissolved via the lungs and the blood in the tissues of the organism in greater quantities than those which may exist there at surface pressure, and that too rapid decompression would release in situ, rather than in the exhalation gases via the blood and the lungs, the excess of said gases not consumable by the body in the form of bubbles called " pathological ", that is to say capable of inflicting lesions on the tissues in which they appear and / or of interrupting the blood circulation in certain vessels, the spectrum of observable and generally deferred consequences of these decompression accidents ranging from slight itching localized until death.

The two main types of decompression are continuous decompression and step decompression.

Continuous decompression consists in reducing the ambient pressure continuously or in small steps, and is faster but less practical than decompression in stages, which consists in making stops of relatively long duration at relatively distant predetermined ambient pressures. one from the other, generally spaced 3 mem (meters of seawater) 3 ms to the surface, the speed of movement to the first level and between the levels being limited by a given maximum admissible value, generally between 10 and 20 mem / min.

Whatever type of decompression is used, the ideal decompression program is the minimal program, that is to say the one whose total duration is the shortest without compromising the safety of the person concerned.

The reasons for this are obvious, especially in the professional diving environment where a few tens of minutes lost in unnecessary decompression time can lead to losses of several thousand francs due to the high hourly cost of divers and the people and equipment that surround.

A method for determining decompression programs is precise when the program prescribed by this method for a given exposure comes as close as possible to the minimum program, any deviation going in the direction of safety.

Two critical factors limit the accuracy of a given method.

The first is the accuracy of determining the state of saturation of the person with non-metabolizable gases after a given exposure.

The second is the precision with which the constraints which said saturation state must obey during decompression are known to avoid the appearance of pathological bubbles.

These two factors are not independent; indeed, the larger the errors made in determining the state of saturation, the more severe must be the constraints to which the said state must be subjected during decompression if one wishes to avoid a sub-minimal decompression and therefore pathological.

The method of the invention has a better first factor and, in turn, a better second factor than conventional methods.

Before describing how this is accomplished, it is necessary to explain in more detail the conventional methods.

These methods, whether they are applied to fictitious ambient pressure scenarios such as for the establishment of decompression tables or to the actual profile of an exposure as in apparatuses of the analog or digital decompression type, are numerous but all have, or at least the most reliable and therefore the most used, a common basic architecture due to the pioneering work of British physiologist JS Haldane at the beginning of this century:

The state of saturation of the organism is represented by the tensions of non-metabolizable gases in a certain number of tissues. These voltages represent concentrations of dissolved gas scaled so that at Saturation of a given tissue for a given gas (Saturation will be used here with a capital S in the sense of equilibrium where the tissue contains in solution all the gas which can reside therein in a stable manner), the tension of the gas in the tissue is numerically equal to the partial pressure of said gas in the breathed mixture, itself equal to the product of ambient pressure and the molar concentration of the gas in the mixture.

These tissues do not represent well defined anatomical tissues, but rather sets of diverse anatomical tissues united by a common behavior with regard to the dynamics of exchanges of a given non-metabolizable gas with respiratory gases.

The necessarily finite number of tissues taken into account by the various methods constitutes a sampling which is intended to be representative of the theoretically almost infinite number of such possible sets.

Each tissue is characterized for a given gas by a constant called period or half-life, which according to the tissue can range from a few minutes to a few hundred minutes, which is defined as the time necessary for the tension of this gas in this tissue reduced by half the difference separating it initially from the saturation tension, equal to the partial pressure of the gas in the respiratory mixture, the latter being assumed to be constant.

où

• q est la tension du gaz dissous dans le tissu
• g est la fraction molaire du gaz dans le mélange
• p est la pression ambiante
• k = Log 2/h est le coefficient exponentiel du tissu où
• Log 2 est le logarithme népérien de 2
• h est la période du tissu ou, si gp et k sont constants, sous la forme intégrée:
• (Eq. 2) q = qo + (gp - qo) (I-exp (-kt))
• où qo est la valeur initiale (au temps 0) et q est la valeur finale (au temps t) de la tension.

This definition implies that the voltage varies exponentially as a function of time t, according to a law which can be expressed differently as follows:

or

• q is the tension of the gas dissolved in the tissue
• g is the molar fraction of the gas in the mixture
• p is the ambient pressure
• k = Log 2 / h is the exponential coefficient of the tissue where
• Log 2 is the natural logarithm of 2
• h is the period of the tissue or, if gp and k are constant, in the integrated form:
• (Eq. 2) q = qo + (gp - qo) (I-exp (-kt))
• where qo is the initial value (at time 0) and q is the final value (at time t) of the voltage.

In addition, certain methods employ calculation devices for estimating the tensions when the ambient pressure is high, such as the "magnification" of the times actually spent at ambient pressures greater than 70 mem by a factor of 1.5 or 2.

The state of saturation of the organism being thus represented, the constraints which it must obey during decompression essentially consist of maximum admissible tensions for each tissue and for each gas which are increasing functions, generally linear but not necessarily passing by the origin, of the ambient pressure, (see US 4,192,001). These maximum allowable voltages at a given ambient pressure for a given gas are greater than said ambient pressure and therefore obviously greater than the partial pressure of the gas at this ambient pressure, thus granting the tissues a certain degree of supersaturation (tension in excess of the saturation voltage) allowed and thus the possibility for at least one of them to desaturate at each stage of decompression, the rate of desaturation being proportional to the amplitude of the supersaturation as indicated ( Eq. 1).

Another constraint which has already been mentioned is the maximum speed of decompression or ascent, which is sufficient to ensure the non-pathological desaturation of the fastest tissues, such as blood.

We know the tables of the laboratory of the pressure chamber of the University of Zurich (Druckkammerlabor der Universitât Zürich) in which the factor of physical effort of the diver is taken into account, that is to say, that a diver making a physical effort underwater can use these tables safely.

In other words, these tables can be qualified as work decompression tables.

This is the case with tables from the French Ministry of Labor.

EP-A-073 499 is also known, according to which the previous dives of a hyperbaric worker are taken into account when calculating the concentration of the inert gas in his tissues.

It should be noted that in all these cases, no physical measurement, other than ambient pressure and time, is taken into account for the determination of the decompression plan.

In order to understand how conventional methods are likely to improve, we can refer for example to paragraph 3.4.1 of research report 6-65 of the US Navy Experimental Diving Unit by RD Workman (1965), where it is essentially says:

"It is also recognized that the admission of inert gas during work is more important than at rest, due to the increase in cardiac output and tissue perfusion. Similarly, the elimination of inert gas during rest periods will be slower than during work.

Determining the maximum allowable voltages from working dives takes this difference into account to some extent ".

The perfusion of anatomical tissue (tissue blood flow) is indeed an important factor in the processes of saturation and desaturation in non-metabolizable gases.

où

Selon ces auteurs, donc, la période de tout tissu varierait en proportion inverse de la perfusion de ce tissu, toutes choses étant égales par ailleurs.Boycott, Damant and Haldane (The prevention of compressed air illness; J. Hyg. Lond. 8, 445-456, 1908) estimate that the characteristic exponential coefficient k of a given tissue for a given gas which, as we have seen, is inversely proportional to the period of this fabric for this gas, can be expressed as follows:

or

According to these authors, therefore, the period of any tissue would vary in inverse proportion to the perfusion of this tissue, all other things being equal.

However, it is nowadays agreed that this would only be true for well-vascularized tissues, and that the periods of poorly vascularized tissues, that is to say those where the gas in solution must diffuse over a comparatively distance long before encountering a blood vessel, would depend more or less on infusions of these tissues.

These latter fabrics would also be those with the longest periods.

The perfusion of a tissue whose metabolism increases, like a muscle providing an effort increases by dilation of the blood vessels which irrigate it in response to temporary hypoxia caused by the said increase in metabolism.

This vasodilatation is accompanied by an increase in cardiac output in order to maintain a constant blood pressure.

Between rest and sustained effort, cardiac output in humans can vary between 5 and 25 I / min, i.e. by a factor of 5, or even more: cardiac outputs of around 40 I / mn have been measured in well trained athletes providing maximum effort.

The simple act of walking slowly increases the cardiac output by about 50% compared to the value at rest.

However, by conserving the flow rates, a muftiplication of the cardiac output by a factor "x" greater than 1 must necessarily be associated with a multiplication by a factor "y" at least equal to "x" of the perfusion of the tissues whose increased metabolism is responsible for the increased cardiac output.

If Boycott, Damant and Haldane are to be believed, this means that the exponential coefficients and therefore the gas exchange rates of said tissues are multiplied by the same factor y ".

Since the factors "x" and therefore "y" can be greater than 5, we see that the errors due to this effect, made by conventional methods in determining the state of saturation of an individual, to which Workman alludes in the extract from his report presented above can be important.

If we consider a simplified model of the organism where the exponential coefficients of all the tissues would vary in proportion to the cardiac output, and if we admit that a diver can work at the bottom at a cardiac output of 25 IImn then decompress then at a cardiac output of 5 I / min according to a conventional method in complete safety - which is doubtful - then it is simple to see, by interchangeability of "k" and "t" in (Eq. 2 ), that the same diver could safely have undergone the same decompression program after a dive at the same depth but lasting 5 times higher if his cardiac output at the bottom was only 5 Vmn, that is that is, if he had made no effort at bottom.

In fact, its state of saturation when it started to rise would have been exactly the same in both cases.

In other words, it would be perfectly safe, in some cases, to use conventional tables by entering a fictitious duration 5 times less than the actual duration of the dive.

For example, if we used the air diving table, annexed to the 1974 decree of the French Ministry of Labor governing the specific protection measures applicable to hyperbaric workers (Official Bulletin, special booklet n ° 74-48 bis) , we could, in some cases, go up safely from a dive of 50 min to 57 m in a total time of 11.4 min (duration of the ascent recommended for a dive of 50/5 - 10 min to 57 m ) which can be compared to the 141.6 min of the decompression program obtained by strict application of the table, thus achieving a significant saving of more than two hours or 92% on the decompression time.

It goes without saying that a diver who would allow himself to be tempted by the saving of time achieved in the example above would run into serious trouble given the simplicity of our hypotheses, which were only intended to provide an order of magnitude of possible impact on actual decompression times of exercise variations during a given exposure to pressure.

On the other hand, it is recognized that the ambient temperature, that is to say the temperature of the medium which receives the plunger, influences the perfusion of the organic tissues. This is how a low temperature reduces tissue perfusion and reduces the speed of gas exchange.

It follows from the above that a diver subjected to a cold environment will have to undergo a slower decompression than when the ambient temperature is moderate.

The purpose of the method according to the invention is to take into account the exercise of the diver and / or the temperature of the ambient environment in order to more accurately determine the optimal decompression program.

Both the diver's exercise and the ambient temperature influence the exchange of non-metabolizable gas between the tissues and the exterior.

A high temperature and / or an increased exercise facilitate this exchange, on the other hand, a slow exercise or a rest and / or a low temperature slow down the said exchange.

Indeed, the factor which influences the exchange of non-metabolizable gas between the different tissues of the body of the diver and the blood (mobile tissue practically in equilibrium with the outside via the lungs) is the perfusion of these different tissues of the body of the diver. .

• - la ventilation pulmonaire,
• - la consommation d'oxygène,
• - la fréquence cardiaque,
• - le débit cardiaque.

The measurement of this for the various tissues is not easy, but its importance can be estimated by observing on the one hand the ambient temperature and on the other hand one of the following parameters:

• - pulmonary ventilation,
• - oxygen consumption,
• - heart rate,
• - cardiac output.

These four parameters are linked together, for different types of subjects and for different types of exercise.

It suffices for example to determine the pulmonary ventilation, to find using known curves the oxygen consumption or the cardiac output.

This pulmonary ventilation can be determined using close measurements of the pressure of the reservoir of the respiratory mixture, then the use of an isothermal expansion law or not to determine the amount of said mixture released by the reservoir.

• 1: Calculer les ventilations pulmonaires (V'E) par l'application d'une loi de détente des gaz comme par exemple:
  
  Où
  • V est le volume du réservoir du dit mélange respiratoire,
  • p est la pression ambiante,
  • dP est la variation de pression du réservoir entre deux mesures successives,
  • dt est l'intervalle de temps entre deux mesures successives,
• 2: Déterminer les débits cardiaques maximaux (Q C) correspondant aux ventilations pulmonaires (V E), ceci à l'aide de tables empiriques préfournies issues d'expériences sur plusieurs sujets à différentes pressions ambiantes,
• 3: Calculer les quantités (qi) de gaz neutre dissous ou gazeux contenues dans un ou plusieurs tissus théoriques (i) constituant un modèle mathématique de l'organisme du plongeur, ceci en intégrant en temps réel écoulé les vitesses d'échanges gaz eux (dqi/dt) des tissus théoriques selon la relation:
  
  où
  • qi est la quantité de gaz neutre présente dans le tissu correspondant (i),
  • Δi est égal à: soit (gp-qi) si qi < (p+Ki) c'est-à-dire en l'absence de bulles dans le tissu (i), soit (gp- (p+K_i)) si q > (p+Ki) c'est-à-dire en présence de bulles dans le tissu (i),
  • g est la fraction molaire du gaz neutre dans le mélange respiratoire,
  • K_i >0 est une constante préfournie déterminée par expérimentation représentant le seuil de formation des bulles dans le tissu (i).
  • k_i est le coefficient de temps du tissu (i) calculable comme:
  • ki =α_i,₁Q _c+ α_i,0 avec ai,1 > 0 si Δi>0 c'est-à-dire une fonction croissante du débit cardiaque dans le cas d'absorption de gaz neutre par le tissu, ou
  • k_i - βi,₁T + β_i,0 avec βi,1 > 0 si Ai < 0 c'est-à-dire une fonction croissante de la température dans le cas d'élimination de gaz neutre par le tissu, αi,1 > 0, αi,0, βi,1 > 0 et βi,0 sont des constantes préfournies déterminées par expérimentation pour un tissu (i),
• 4: Calculer par intégration en temps futur de l'équation (1) en supposant que Q c et T conserveront leurs valeurs, l'évolution future de chaque (qi) correspondant à un tissu (i) dans le cas d'une remontée hypothétique à partir de la pression ambiante actuelle (p) à une vitesse constante habituellement utilisée (par exemple de 10 à 20 m/min) jusqu'à ce que (qi) d'un tissu quelconque atteigne une valeur maximale admissible (qi)max.
• 5: Calculer la profondeur à laquelle (qi) d'un tissu quelconque atteindra une valeur maximale admissible (q)max, où (q_i)max est une fonction empirique préfournie du tissu et de la profondeur, et déterminer le premier (D1) palier comme celui dont la profondeur est égale ou immédiatement supérieure à la dite profondeur calculée.
• 6: Calculer le temps à passer au palier pour que les (qi) de tous les tissus (i) soient inférieurs ou égaux aux (q_i)max du palier suivant, temps à l'issue duquel on peut remonter au palier suivant en un temps court.
• 7: Répéter l'étape (6) jusqu'à l'arrivée à la surface.

To this end, according to a provision of the invention, the method, according to which the time (t), the ambient temperature (T), the ambient pressure (p), and the pressure of the respiratory mixture tank (P) containing a neutral gas such as nitrogen are measured, consists in a first form in:

• 1: Calculate the pulmonary ventilation (V'E) by applying a gas expansion law, for example:
  
  Or
  • V is the volume of the reservoir of said respiratory mixture,
  • p is the ambient pressure,
  • dP is the variation in tank pressure between two successive measurements,
  • dt is the time interval between two successive measurements,
• 2: Determine the maximum cardiac rates (QC) corresponding to the pulmonary ventilations (VE), this using predefined empirical tables stemming from experiments on several subjects at different ambient pressures,
• 3: Calculate the quantities (qi) of dissolved or gaseous neutral gas contained in one or more theoretical tissues (i) constituting a mathematical model of the diver's body, this by integrating in real time the gas exchange speeds ( dqi / dt) theoretical fabrics according to the relation:
  
  or
  • qi is the quantity of neutral gas present in the corresponding tissue (i),
  • Δi is equal to: either (gp-qi) if qi <(p + Ki), i.e. in the absence of bubbles in the tissue (i), or (gp- (p + K _i )) if q> (p + Ki), i.e. in the presence of bubbles in the tissue (i),
  • g is the molar fraction of the neutral gas in the respiratory mixture,
  • K _i > 0 is a predefined constant determined by experimentation representing the threshold for the formation of bubbles in the tissue (i).
  • k _i is the time coefficient of the tissue (i) calculable as:
  • ki = α _i , ₁ Q _c + α _{i, 0} with ai, 1> 0 if Δi> 0 i.e. an increasing function of the cardiac output in the case of absorption of neutral gas by the tissue, or
  • k _i - βi, ₁ T + β _{i, 0} with βi, 1> 0 if Ai <0 i.e. an increasing function of the temperature in the case of elimination of neutral gas by the tissue, αi, 1> 0, αi, 0, βi, 1> 0 and βi, 0 are pre-provided constants determined by experimentation for a tissue (i),
• 4: Calculate by integration in future time of equation (1) assuming that Q c and T will keep their values, the future evolution of each (qi) corresponding to a tissue (i) in the case of a hypothetical rise from the current ambient pressure (p) at a constant speed usually used (for example from 10 to 20 m / min) until (qi) of any tissue reaches a maximum admissible value (qi) max.
• 5: Calculate the depth at which (qi) of any tissue will reach a maximum admissible value (q) max, where (q _i ) max is a predefined empirical function of the tissue and the depth, and determine the first (D1) level like that whose depth is equal to or immediately greater than said calculated depth.
• 6: Calculate the time to pass at the level so that the (qi) of all the tissues (i) are less than or equal to the (q _i ) max of the next level, time at the end of which we can go up to the next level in one short time.
• 7: Repeat step (6) until reaching the surface.

• - dans le cas d'absorption de gaz neutre par le tissu, la vitesse d'absorption dépend de l'exercice mais pas de la température. En effet, dans un but de sécurité, seul le facteur succeptible d'accélerer l'absorption est pris en compte.
• - dans le cas d'élimination de gaz neutre, la vitesse d'élimination dépend de la température mais par de l'exercice. En effet, toujours dans un but de sécurité, seul le facteur succeptible de ralentir l'élimination est pris en compte,
• - la prise en compte de la présence éventuelle de bulles à travers le paramètre K dans le calcul du gradient Δi répond également à un objectif de sécurité puisqu'elle tend à ralentir l'élimination.

Three important points should be noted concerning equation (1) which governs the gas exchange of tissues:

• - in the case of absorption of neutral gas by the tissue, the speed of absorption depends on the exercise but not on the temperature. In fact, for safety reasons, only the factor capable of accelerating absorption is taken into account.
• - in the case of elimination of neutral gas, the elimination speed depends on the temperature but through exercise. In fact, always for safety reasons, only the factor capable of slowing down elimination is taken into account,
• - taking into account the possible presence of bubbles through the parameter K in the calculation of the gradient Δi also meets a safety objective since it tends to slow elimination.

• - mémoriser la plus forte valeur de la ventilation calculée (V E)max,
• - mémoriser la plus forte pression ambiante mesurée et en déduire la profondeur maximale atteinte,
• - mémoriser la plus basse température (T)min mesurée,
• - sélectionner une table de décompression du travail comme par exemple la table du ministère français du travail si (V E)max est supérieure à une valeur consignée de ventilation pulmonaire ou si (T)min est inférieure à une valeur consignée de température,
• - sélectionner une table de décompression d'exploration comme par exemple la table du GERS (Marine Française) si (V E)_max est inférieure à la dite valeur consignée de ventilation pulmonaire et si (T)min est supérieure à la dite valeur consignée de température,
• - extraire de la table sélectionnée le plan de décompression correspondant à la profondeur maximale atteinte et au temps de plongée mesuré (t).

In a simplified form, the method consists in:

• - memorize the highest value of the calculated ventilation (VE) max,
• - memorize the highest ambient pressure measured and deduce the maximum depth reached,
• - memorize the lowest measured temperature (T) min,
• - select a work decompression table such as for example the table of the French Ministry of Labor if (VE) max is greater than a set value for pulmonary ventilation or if (T) min is less than a set value for temperature,
• - select an exploration decompression table such as the GERS (French Navy) table if (VE) _max is less than the said setpoint value for pulmonary ventilation and if (T) min is greater than the said setpoint temperature ,
• - extract from the selected table the decompression plan corresponding to the maximum depth reached and the measured dive time (t).

The recorded value of the pulmonary ventilation can have as acceptable value 40 liters / min and that of the temperature 10 ° C.

• 1: un moyen pour mesurer le temps (t) produisant des signaux représentatifs du dit temps, 2: un moyen pour mesurer la température ambiante (T) produisant des signaux représentatifs de la dite température,
• 3: un moyen pour mesurer la pression ambiante (p) produisant des signaux représentatifs de la dite pression,
• 4: un moyen pour mesurer la pression du réservoir (P) du mélange respiratoire produisant des signaux représentatifs de la dite pression,
• 5: des moyens d'introduction de données permettant notamment l'entrée du volume du réservoir de gaz respiratoire et le choix de l'une ou de l'autre méthode de calcul du plan de décompression.
• 6: des moyens de calcul automatique à mémoires recevant les signaux de sortie des moyens de mesure et des moyens d'entrée de données:
  • a) calculant la ventilation pulmonaire (V E),
  • b) choisissant une table de décompression à utiliser parmi deux tables de décompression préenregistrées, ceci après avoir comparé la valeur de ventilation maximale calculée avec une valeur consignée de ventilation et la valeur minimale de température avec une valeur consignée de température et extrayant de la table choisie le plan de décompression correspondant au temps de plongée mesuré et à la profondeur maximale mesurée, ou, calculant par intégration en temps écoulé et en temps futur les valeurs de la concentration du gaz neutre dans les différents tissus et établissant le plan de décompression,
  • c) produisant des signaux de sortie représentatifs du plan de décompression déterminé,
• 7: des moyens d'indication recevant les signaux de sortie des moyens de calcul.

According to another arrangement of the present invention, the automatic device for determining and indicating an optimal decompression plane, according to the method, is characterized in that it comprises:

• 1: a means for measuring time (t) producing signals representative of said time, 2: a means for measuring ambient temperature (T) producing signals representative of said temperature,
• 3: a means for measuring the ambient pressure (p) producing signals representative of said pressure,
• 4: a means for measuring the pressure of the reservoir (P) of the respiratory mixture producing signals representative of said pressure,
• 5: data input means allowing in particular the entry of the volume of the respiratory gas reservoir and the choice of one or the other method of calculating the decompression plane.
• 6: automatic calculation means with memories receiving the output signals from the measurement means and data input means:
  • a) calculating pulmonary ventilation (VE),
  • b) choosing a decompression table to be used from two prerecorded decompression tables, this after having compared the maximum ventilation value calculated with a recorded ventilation value and the minimum temperature value with a recorded temperature value and extracting from the chosen table the decompression plan corresponding to the dive time measured and the maximum depth measured, or, calculating by integration in elapsed time and in future time the values of the concentration of neutral gas in the different tissues and establishing the decompression plan,
  • c) producing output signals representative of the determined decompression plane,
• 7: indication means receiving the output signals from the calculation means.

• - un capteur de pression du réservoir du gaz respiratoire (P) connecté au dit réservoir par un tuyau flexible et produisant un signal représentant la dite pression,
• - un capteur de pression ambiante (p) dont l'emplacement est non critique produisant un signal représentant la dite pression,
• - un multiplexeur dont certaines entrées sont connectées à la sortie du capteur de pression du gaz respiratoire et à la sortie du capteur de pression ambiante et dont la sortie communique les dits signaux l'un après l'autre dans un cycle répétitif à un convertisseur analogique numérique,
• - un convertisseur analogique numérique dont l'entrée est reliée à la sortie du muftiplexeur et dont la sortie est reliée à un micro-processeur,
• - un micro-processeur recevant du convertisseur analogique numérique des valeurs successives de pressions mesurées à des intervalles prédéterminés et calculant par la suite la ventilation pulmonaire.

According to a characteristic of the present invention, the pressure measurement means and the calculation means for calculating, inter alia, pulmonary ventilation are constituted by:

• a pressure sensor of the respiratory gas reservoir (P) connected to said reservoir by a flexible hose and producing a signal representing said pressure,
• - an ambient pressure sensor (p) whose location is non-critical producing a signal representing said pressure,
• - a multiplexer, certain inputs of which are connected to the output of the respiratory gas pressure sensor and to the output of the ambient pressure sensor, and the output of which communicates said signals one after the other in a repetitive cycle to an analog converter digital,
• - an analog to digital converter whose input is connected to the output of the muftiplexer and whose output is connected to a microprocessor,
• - a microprocessor receiving successive values of pressures measured at predetermined intervals from the analog-to-digital converter and subsequently calculating pulmonary ventilation.

According to another characteristic, the memories of the automatic calculation means with memories include data representative of those of the table of GERS (French Navy) and those of the table of the French Ministry of Labor or any other tables.

According to another characteristic, the memories of the memory calculation means equipping the device contain the data of a program of calculation in real time and in future time of the quantities of neutral gas present in the theoretical tissues.

According to another characteristic, the device comprises registers for receiving the highest value of pulmonary ventilation, the lowest value of the ambient temperature, the value of the highest ambient pressure experienced by the diver and the value of the dive time, the means of calculation based on the value of the minimum ambient temperature and the value of the maximum pulmonary ventilation received by the registers, selecting either the GERS table or the table of the French Ministry of Labor and subsequently according to the value of the highest ambient pressure determining the maximum diving depth and the value of the diving time selecting the corresponding decompression plane in the selected table.

According to another characteristic, the device comprises two solenoid valves controlled by the calculation means, one having its input connected to a gas tank other than the respiratory gas tank and its output connected to an inflatable or equivalent vest and the other having its input connected to said vest and its output left to the atmosphere, the calculation means controlling one or other of the valves to inflate the said vest or to deflate it in order to perform an automatic ascent, this being following the observation of a any anomaly according to pre-recorded instructions either following a voluntary order given on the spot.

According to another arrangement of the present invention, the diving assembly forming part of the present invention, is characterized in that it incorporates a device applying the present method.

Knowing P has other obvious safety advantages by allowing good management of respiratory reserves.

où

• Ps est la valeur de P prédite à l'arrivée en surface
• Po est la présente valeur de P
• x0 est la valeur présumée constante de la ventilation (respectivement consommation d'oxygène) lors de la décompression.

This management is made all the easier since the present method makes it possible, thanks to the simultaneous knowledge of P and of the decompression program, to predict the value of P on arrival at the surface by application of the following equation obtained by integration. of (Eq 4):

or

• Ps is the value of P predicted on arrival at the surface
• Po is the present value of P
• x0 is the presumed constant value of ventilation (respectively oxygen consumption) during decompression.

In order to increase for safety reasons the pressure drop P-Ps, a relatively high value may be used, for example 20 I / min (respectively 1 Vmn).

The word "prog" under the integral sign if- gn ⁱ trust that integration is performed on the pressure profile ambianteltemps decompression program.

Naturally, this prediction can be made by preceding the ascent of a hypothetical residual stay at the present depth at the end of which the new state of saturation and the new decompression program are calculated as for an actual stay, so that one can predict by successive tests the maximum possible residual time at this depth, taking into account the available breathing gas reserves.

Other advantages and characteristics of the invention will appear on reading the description of a preferred embodiment given by way of nonlimiting example with reference to the appended drawing which shows a block diagram of the device according to the invention.

As mentioned above, the method, part of the invention, takes into account as exercise parameter, the pulmonary ventilation (VE) determined during the dive, to calculate the quantities (qi) of neutral gas contained in one or more theoretical tissues (i) constituting a mathematical model of the diver's body.

Où

• V est le volume du réservoir du mélange respiratoire,
• p est est la pression ambiante,
• dP est la variation de pression du réservoir entre deux mesures successives,
• dt est l'intervalle de temps entre deux mesures successives.

In fact, this pulmonary ventilation (VE) is equal to the flow of the respiratory mixture released by the reservoir. This breakdown is calculated as:

Or

• V is the volume of the respiratory mixture reservoir,
• p is is the ambient pressure,
• dP is the variation in tank pressure between two successive measurements,
• dt is the time interval between two successive measurements.

Once the pulmonary ventilations are determined, the corresponding maximum cardiac rates (Q c) are determined using the empirical tables provided from experiments on several subjects at different ambient pressures.

These are the maximum cardiac rates which are used, among other things, for the calculation of the quantities (qi) of neutral gas dissolved or not contained in the various theoretical tissues (i) constituting the mathematical model of the diver's body.

It should be noted that these maximum cardiac rates can be determined otherwise; the pul- sat ⁱ ons heart are measured and the maximum cardiac output are determined using the préfournies correspondence tables.

The determination of the maximum cardiac rates can be indifferently carried out by any of these two methods.

Selon que Δi est positif (absorption de gaz neutre par le tissu) ou négatif (élémination de gaz neutre par le tissu), le coefficient de temps k_i du tissu (i) est calculable comme:

• ki = αi,1 Q c + αi,0 avec αi,1 > 0
• dans le premier cas (Δi > 0) ou comme:
  
• dans le deuxième cas (Ai < 0)

We calculate the quantities of neutral gas (qi) contained in one or more theoretical tissues (i) constituting a mathematical model of the diver's body by integrating in real time elapsed gas exchange rates (dqi / dt) of theoretical fabrics according to relation (1):

Depending on whether Δi is positive (absorption of neutral gas by the tissue) or negative (elimination of neutral gas by the tissue), the time coefficient k _i of the tissue (i) can be calculated as:

• ki = αi, 1 Q c + αi, 0 with αi, 1> 0
• in the first case (Δi> 0) or as:
  
• in the second case (Ai <0)

• -Si qi < p + Ki, c'est-à-dire en l'absence de bulles de gaz neutre dans le tissu (i), où p est la pression ambiante et Ki est le seuil de formation de bulles de gaz neutre dans le tissu (i),
• Δ_i est calculable comme:
• Δ_i = gp, qi g est la fraction molaire du gaz neutre dans le mélange respiratoire
• - Si qi > p + Ki, c'est-à-dire en présence de bulles de gaz neutre dans le tissu (i)
• Ai est calculable comme:
  
  Pour établir le plan de décompression, on calcule l'évolution future de chaque (qi). correspondant à un tissu (i), en supposant que Q c et T conserveront leurs valeurs, ceci par intégration en temps futur de l'équation (1) dans le cas d'une remontée hypothétique à partir de la pression ambiante actuelle à une vitesse constante habituellement pratiquée (par exemple de 10 à 20 m/min) jusqu'à ce que (qi) d'un tissu quelconque atteigne une valeur maximale admissible (qi)max, celle-ci étant une fonction empirique préfournie du tissu et de la profondeur.

where αi, 1> 0, α _{i, 0} , βi, 1> 0 and β _{i, 0} are pre-provided constants determined by experimentation for each tissue (i).

• -If qi <p + Ki, i.e. in the absence of bubbles of neutral gas in the tissue (i), where p is the ambient pressure and Ki is the threshold for the formation of bubbles of neutral gas in the fabric (i),
• Δ _i can be calculated as:
• Δ _i = gp, qi g is the molar fraction of the neutral gas in the respiratory mixture
• - If qi> p + Ki, i.e. in the presence of bubbles of neutral gas in the tissue (i)
• Ai is calculable as:
  
  To establish the decompression plan, we calculate the future evolution of each (qi). corresponding to a tissue (i), assuming that Q c and T will keep their values, this by integration in future time of equation (1) in the case of a hypothetical rise from the current ambient pressure at a speed constant usually practiced (for example from 10 to 20 m / min) until (qi) of any tissue reaches a maximum admissible value (qi) max, this being a predefined empirical function of the tissue and the depth.

The first stage (D1) is determined as that whose depth is equal to or immediately greater than the depth where any one of (q _i ) max is reached.

We calculate the time to pass to the depth at the level so that the (qi) of all tissues (i) are less than or equal to the (qi) max of the next level, time after which we can go back to said next level in a short time.

This last step is repeated until arriving at the surface.

According to a simplified form of the present process, the quantities of neutral gas (qi) relating to the tissues (i) are not calculated.

Indeed, a decompression table either for work (as for example the table of the French Ministry of Labor) or for exploration (as for example the table of GERS of the French Navy) is selected according to the values of the pulmonary ventilation determined and measured room temperature values.

• - mémoriser la plus forte valeur de la ventilation pulmonaire déterminée (V E)max.
• - mémoriser la plus basse température mesurée, (T)min.
• - sélectionner une table de décompression du travail si (V«E)max est supérieure à une valeur consignée de ventilation pulmonaire ou si (T)min est inférieure à une valeur consignée de température,
• - sélectionner une table de décompression d'exploration si (V E)max est inférieure à la dite valeur consignée de ventilation et si (^T)min est supérieure à la dite valeur consignée de température,
• - extraire de la table sélectionnée le plan de décompression correspondant à la profondeur maximale atteinte et au temps de plongée mesuré (t).

This simplified form of the process consists of:

• - memorize the highest value of the determined pulmonary ventilation (VE) max.
• - memorize the lowest measured temperature, (T) min.
• - select a work decompression table if (V "E) max is greater than a set value for pulmonary ventilation or if (T) min is less than a set value for temperature,
• - select an exploration decompression table if (VE) max is less than said set ventilation value and if ( ^T ) min is greater than said temperature set value,
• - extract from the selected table the decompression plan corresponding to the maximum depth reached and the measured dive time (t).

According to this simplified form of the process, the recorded values of ventilation and temperature are 40 liters / minute for pulmonary ventilation and 10 ° C for temperature for example.

The device implementing the method according to the present invention comprises means for measuring the time (t), the ambient temperature ( ^T ), the ambient pressure (p), the pressure (P) of the reservoir of the respiratory mixture.

These means each produce signals representing the corresponding parameter.

Measuring the pressure of the respiratory mixture reservoir (P) and the ambient pressure (p) as a function of time (t) makes it possible to determine the pulmonary ventilation and therefore the cardiac output.

In what follows, the description of the device will be limited to the embodiment, where the cardiac output is determined by determining the pulmonary ventilation, but it should be noted that said flow can also be determined by measuring the frequency diver's heart.

In the latter case, the device forming part of the present invention is equipped with a cardiac pulse sensor, known per se, producing signals representative of said pulsations.

The corresponding cardiac rates are found using the pre-provided correspondence tables.

The device also includes data input means allowing data entry to choose a decompression plan calculation method and to serve for the determination of said plan; the volume of the respiratory gas reservoir is introduced to serve, among other things, for determining pulmonary ventilation.

• a) calculant la ventilation pulmonaire (V E),
• b) choisissant une table de décompression à utiliser parmi deux tables de décompression préenregistrées, ceci après avoir comparé la valeur de ventilation maximale calculée avec une valeur consignée et la valeur minimale de température mesurée, avec une valeur consignée de température et extrayant de la table choisie le plan de décompression correspondant au temps de plongée mesuré et à la profondeur maximale mesurée, ou, calculant par Intégration en temps écoulé et en temps futur les valeurs de la concentration du gaz neutre dans les différents tissus et établissant le plan de décompression,
• c) produisant des signaux de sortie représentatifs du plan de décompression déterminé.

The device according to the present invention also comprises means of automatic calculation with memories receiving the output signals from the measurement means and data input means:

• a) calculating pulmonary ventilation (VE),
• b) choosing a decompression table to be used from two prerecorded decompression tables, this after having compared the calculated maximum ventilation value with a recorded value and the minimum value of measured temperature, with a set temperature value and extracting from the chosen table the decompression plan corresponding to the measured dive time and the maximum depth measured, or, calculating by Integration in elapsed time and in future time the concentration values of the neutral gas in the various tissues and establishing the decompression plane,
• c) producing output signals representative of the determined decompression plane.

The device also includes indication means receiving the output signals from the calculation means.

According to a first embodiment, the memories of the calculation means include instructions necessary to calculate the quantities (qi) of neutral gas contained in one or more tissues (i), this by the integration in real time of the exchange rates gaseous of said tissues.

This calculation takes into account the ambient pressure, the time and the ambient temperature and is performed each time the pulmonary ventilation is determined from successive measurements of the pressure of the respiratory gas reservoir.

The pulmonary ventilation itself is, according to stored instructions calculated from said measurements and according to an isothermal expansion law or not, known in itself, and taking into account the volume of said tank, the ambient pressure and possibly the evolution of the temperature as a function of time.

The decompression plan is finally determined by integration in future time of the said gas exchange rates, also following the instructions stored according to the present process.

The permanent calculation of the quantities (q;) of neutral gas in the various tissues (i) makes it possible to update the decompression plan according to the actual progress of the ascent and possibly in the case of the execution of successive dives at sea, at altitude or speleological.

According to a second embodiment, the memories of the calculation means comprise the data of at least two decompression tables, for example the table of GERS and the table of the French Ministry of Labor.

According to this embodiment, the device also comprises two registers for receiving the highest value of the pulmonary ventilation and the lowest value of the ambient temperature.

The device also has two other registers for receiving the highest value of the ambient pressure and the value of the dive time.

The calculation means, according to the value of the minimum ambient temperature and the value of the maximum pulmonary ventilation recorded in these registers, select either the GERS table or the table of the French Ministry of Labor.

For example, the GERS table is selected if the ambient temperature has never been below 10 ° C and if the pulmonary ventilation has never been above 40 liters / minute.

The calculation means extract from the selected table the decompression plan corresponding to the dive time and the maximum depth reached, these calculation means, by means of indication means indicate to the diver the parameters fixing the stages of decompression (stages and durations of the stages).

It is interesting to note that by means of the measurement means the device automatically detects the fact that the diver ascends, checks whether the diver follows the indications of the decompression plane and is therefore able to warn him via the means of indication if this is not the case, and of updating the decompression program according to the actual progress of the decompression.

It should be noted that the first embodiment can coexist with the second to take over in the event that the diving profile goes beyond the framework of the prerecorded tables.

The device comprises a means for measuring the ambient pressure, a means for measuring the time, a means for measuring the ambient temperature and a means for measuring the exercise.

By way of example, the device according to the invention comprises at least one means for measuring the pulmonary ventilation to determine the exercise.

Preferably the pulmonary ventilation is determined by measuring the rate of decrease of the pressure P of the respiratory gas reservoir according to (Eq. 4).

The calculation means and possibly the indication means are sensitive to the signals coming from said pressure measurement means P.

Said calculating means evaluate the rate of variation of the pressure P as a function of the signals coming from said means for measuring the pressure P and from those coming from the time measuring means at the ends of a small time interval.

Said calculation means determine the pulmonary ventilation of the user as a function of said rate of variation of P, of the ambient pressure, and of the volume of the reservoir concerned.

The calculation means also use the current measured value of the pressure P to predict, on the basis of and possibly simultaneously with the current decompression program, the value of P when it reaches the surface assuming that the user would immediately perform its ascent according to the indications of the device and where its pulmonary ventilation during said ascent would have a presumed given value, said value may or may not depend on the values measured until the time when the prediction is made.

Said calculation means are able to warn the user by means of one or more of the indication means as soon as the value P predicted upon arrival at the surface becomes less than a given safety threshold.

The above prediction is also effective. killed by preceding the ascent of a hypothetical residual stay at this depth, at the end of which the new state of saturation and the new decompression program are calculated as for an actual stay, so that the means of calculation predict by suc - cess ⁱ fs the maximum possible residual duration at this depth, taking into account the available breathing gas reserves.

The means for measuring the ambient pressure, the ambient temperature, and the pressure of the bottle or bottles each comprise at least one sensor which delivers an analog electrical signal and at least one analog digital converter which receives the analog electrical signal and the converts to digital signal.

In addition, the means for measuring the ventilation in combination with the bottle pressure sensor and the analog-to-digital converter comprises a programmable clock or timer so that the calculation means in relation to the programmable clock can assess the speed of variation. pressure in the bottle.

Preferably the bottle pressure sensor is connected to said bottle by a flexible hose.

Advantageously, the outputs of these sensors are connected to at least one multiplexer controlled by the calculation means, the output of this multiplexer is electrically connected to the input of the analog to digital converter.

By means of the multiplexer, the calculation means select the outputs of the various sensors sequentially.

The sensors of the pressure measurement means are reactive or resistive, electro-mechanical or electrical, passive or active, precalibrated or not, with or without internal thermal compensation for sensitivity and / or zero, sensitive to pressures absolute or pressures relative to that prevailing inside the housing or one of its compartments. They may or may not include bellows, Bourdon tubes, levers, converters for displacement into an electrical signal, membranes, intermediate fluids transmitting pressure, flexible or rigid pipes or conduits equipping the sensitive parts of the sensors and the environments where pressures are measured. Their electrical part can be composed of one or more discrete or integrated electronic elements, which can behave electrically like a "Wheatstone bridge" whose resistance of one or more of the branches varies according to the measured pressure thus varying the output voltage of said bridge, or as a differential electric oscillator or not, the impedance of one or more of the elements of which varies as a function of the pressure measured, thus varying the oscillation frequency of said oscillator.

Said means for measuring the pressure or pressures can also include circuits for amplification and / or external thermal compensation of the input (excitation) and / or output signals of the base sensor (s).

These circuits can be integrated into a single component or consist of operational amplifiers and passive components (resistances, capacitors).

These circuits may also be common to the other sensors by insertion of one or more analog demultiplexers and / or muftiplexers controlled by the calculation means between said circuits and the inputs and / or outputs of said sensors.

Said means for measuring the pressure or pressures may comprise at least one constant voltage source, the output of which is connected either directly or by means of the said amplification and / or thermal compensation circuits at the input (excitation) of the sensor (s), said constant voltage source which, according to an arrangement called "ratiometric", can be that which internally or externally calibrates the analog-digital converter (s).

The ambient temperature sensor is of the resistive temperature detector (RTD), thermistor, thermocouple, diode or integrated circuit type.

Said means for measuring the temperature may have parts in common with other elements of the device, the temperature sensor being able in particular to be integrated into one of the pressure sensors or to the analog-to-digital converter being able to be of the voltage-frequency type.

It is interesting to note that the signals from the temperature measurement means can be used to compensate for the thermal coefficients of the other measurement means and possibly of the indication means.

These compensations can be performed analogically, either by direct excitation of the member to be compensated by the output voltage of said temperature measurement means, or by the use of operational amplifiers which may or may not be part of amplifier stages.

These compensations can also be carried out digitally in which case the temperature measurement means comprise at least one analog-digital converter which can be of the voltage-frequency type which they can share with other measurement means if an analog multiplexer is provided. assistant, the output or outputs of said converter being connected to one or more lines of the calculation means, said converter also being able to contain the base temperature sensor.

The indication means can be directly sensitive, via amplification circuits or via calculation means, to signals from the temperature measurement means and capable of informing the user of the value of said temperature.

As said before, a possible version of the device also includes a means measuring heart rate.

By way of example, this means is constituted by a pulse sensor of a known type which is sensitive to the cardiac pulse and which transforms the said pulse into an electrical pulse.

This means is also constituted by the programmable clock or "timer" which measures by means of an interruption line of the microcomputer the time interval between two electrical pulses received.

There is a pulse shaping circuit at the output of the heart rate sensor.

This circuit can for example be a flip-flop of the "Schmidt trigger" type.

Advantageously, the heartbeat sensor is mounted in a bracelet intended to be attached to the wrist of the diver.

An electrical line consisting of an electrical wire coated with an insulator connects this sensor to the rest of the device.

The means of data entry allow the possible modification, for purposes of experimentation or adaptation to new diving conditions or simply for reasons of personal preferences, of some of the quantities that can be held explicitly or implicitly in the memory of the means calculation such as surface pressure, volume of the tank in which the pressure P is measured, type of respiratory system used, safety threshold of the pressure P predicted on arrival at the surface, composition of the respiratory mixture possibly below form of a function of the ambient pressure, number and basic periods (for a given basic cardiac output) of the tissues constituting the mathematical model of the organism, initial values of the tensions of the various non-metabolizable gases in said tissues, maximum values permissible of said voltages as functions of ambient pressure, maximum ascent rate male, desired decompression mode (continuous or stepwise), depths or ambient pressures authorized for the execution of steps in the case of step decompression, coefficients of the correlation cardiac output / pulmonary ventilation / ambient pressure, coefficients correlation of cardiac output / period for each tissue, dive time not to be exceeded, depth or ambient pressure not to be exceeded, calibration constants of the measurement means, thermal coefficients of sensitivity and / or zero of the measurement means and / or indication means, desired indication mode, optimum reading angle and / or display illumination request in the case of a liquid crystal display.

For example, the data input means are composed of magnetic action switches of the "reed" or Hall effect type located inside the housing, controlling the binary state of lines of the calculation means and one or more several magnets encapsulated in or covered with a material suitable for protecting them from corrosion, located outside said housing and movable in translation and / or rotation by the user in order to actuate said switches selectively and remotely.

The data entry means may also include a locking device to protect the constants against any accidental modification during use or transport of the device.

The calculation means are for example constituted by a microcomputer which can be of CMOS construction comprising in one or more housings one or more microprocessors with 4, 8, 16, 32 or even 64 bits, one or more clock signal generators, one or more elements of random access memory which can be of the static or dynamic type or a combination of the two, possibly one or more elements of read-only memory programmable or not, possibly one or more "timers" (counting registers), possibly one or more decoders , possibly one or more binary signal amplifiers ("buffers", "drivers", buffers, transmitters, receivers, transmitters) possibly one or more auxiliary logic boxes (gates, inverters, movable, muftiplexers, counters, Schmidt flip-flops) possibly one or more passive components (resistors, capacitors), possibly one or more communication interfaces, programmable or not, parallel (PIA, -PIO) or synchronous or asynchronous series (SCI, UART, USART, ACIA). The said clock signal generator (s) allow the said microprocessor (s) to execute in sequence the machine code instructions stored in memory (dead or living fault) of which the various operations for entering, processing and transmitting information assigned to are made up. means of calculation.

The RAM can be kept under permanent voltage so that its content is preserved even during periods of device shutdown. The microprocessor (s) can operate in various modes such as "active", "sleep", "standby" corresponding to various energy levels.

The calculation means can have one or more hierarchical or non-hierarchical interruption facilities, maskable or not, internal and / or external, by hardware and / or software, allowing the execution of specific algorithms according to the state of the measurement means. and / or display means and / or the timer (s) if necessary and / or data input means if necessary and / or means for supplying electrical energy.

One of said interruption facilities, preferably of the non-maskable type, controlled by the data input means, can trigger an organized system closure procedure which guarantees the backup of the contents of the RAM.

The timers if present can fulfill all or part of the functions of the means of on time in association with the clock signal generator (s). The clock signal generator (s) can be composed of independent oscillators (crystalline, for example quartz, or others, for example RLC circuits) or outputs from those of the time measurement means, if any, which are separate from the means of calculation. The communications between the various components, if there are several, of the calculation means (internal communications) and between the calculation means and the other components of the device (input-output communications) take place via programmable ports. or not, with or without latch ("latches"), one-way or two-way or mixed, which may have an inhibition facility (high impedance state) and / or via interrupt lines (by example for reception of frequency type signals) and / or via control lines (such as selection lines, handshake lines) and / or via parallel or serial communication interfaces. Some of these ports can be interconnected in a so-called "bus" arrangement. The input-output ports can be specialized or projected in memory. Said calculation means can fulfill part of the functions of the various measurement means, in particular by performing thermal calibrations and / or compensations of sensitivities and / or zeros, by generating via digital-analog converters analog signals allowing to evaluate the signals to be measured by using comparators or by measuring the frequency of an alternating signal using a "timer" and the associated external capture facility ("input capture interrupt"). Said calculation means can modify one or more excitation voltages of the measurement and / or indication means by means of digital-analog converters or analog multiplexers associated with potential dividers and possible operational amplifiers. and passive components in order, for example in the case of a liquid crystal display, to modify the optimum reading angle in order to satisfy the requests expressed by the user via the data entry means or in order to keep said angle constant by compensating for the thermal effects that affect it. The sequences of instructions executed by said calculation means may include various tests of the correct functioning of the device, in particular likelihood tests, leading to a warning of the diver via the indication means in the event of a malfunction detected.

Said calculation means can, thanks to one or more switches of the “sotid-state” type (for example Dartingtons or power Mosfets) or mechanical relays (for example of the “reed” type) selectively or globally control the supply of electrical energy other components of the system, in order to direct their operation (on / off of lamps, horns, etc.) and / or to save energy for example by temporarily deactivating certain measurement means while the output signals of said means measurement are not "online" (active on the input lines of the computing means) or when said output signals are observed, vary very slowly allowing infrequent sampling.

The means for supplying electrical energy are, for example, constituted by rechargeable batteries of the cadmium-nickel type or non-rechargeable batteries of the lithium or mercury type.

Said means for supplying electrical energy occupy, for example, a separate and possibly detachable and replaceable compartment of the housing, hermetically isolated from the other compartment or compartments of said housing while being electrically connected to them.

Said supply means if they are of the rechargeable type are connected to two stainless steel contacts, for example gold or gold-plated contacts located outside the housing and allow recharging of said supply means, at least one of the two connections by means of a diode or a switch preventing the discharge of said supply means via said contacts in seawater or in the ambient environment of the user, whoever it may be, the switch, in the case of a switch that can be of the reed type controlled from the outside of the housing using a magnet by the user or a relay controlled by the calculation means as a function of the ambient pressure, and / or requests expressed by the user via the data entry means.

The compartment of the box containing the said supply means is provided with a manual opening or with a valve for the elimination of gases released by the supply means while preventing the entry of fluids or foreign bodies.

The device of the invention may also include means for determining the state of charge of the supply means. These determination means consist of a constant voltage source, possibly a potential divider to which the potential difference is applied between the terminals of said supply means, and a comparator or more simply a divider of voltage connected to an additional input of the analog multiplexer downstream of the analog-digital converter. These means are totally or partially integrated into a single component, the output or outputs of said determination means being connected to one or more ports of the calculation means and / or to the indication means. The means of determining the state of charge trigger, after possible expiration of a delay and possible warning of the diver via the indication means, an organized closure of the system guaranteeing the backup of the contents of the RAM.

The means of indication are made up of visual, sound or tactile means.

The visual means comprise one or more simple light emitting diodes or arranged in segment display and / or dot matrix and / or "bar-graphs", one or more reflective, transmitive or transflective liquid crystal displays, with direct excitation or multiplexed, illuminable or not, with segments and / or matrices of predefined points and / or symbols and / or "bar-graphs", one or more plasma screens, one or more cathode-ray tube screens, one or more dials with needles, one or more incandescent lamps, one or more flash lamps, one or more electroluminescent tubes or screens, painted and / or engraved legends. These visual means are apparent to the user through one or more windows or transparent walls of the housing and are capable of representing, in digital or analog form or as a "bar-graph" or binary (display in two states, such as an LED s illuminating when a certain quantity exceeds a certain threshold) simultaneously or alternatively, automatically or on request via the data input means, any combination of the following information that the calculation means and possibly the measurement means are capable of provide them with:

full or partial decompression program consisting of couples (depth or ambient pressure, time) and possibly the total duration of the ascent, minimum depth or ambient pressure accessible for continuous decompression, duration of this dive (stay at pressures higher than that prevailing on the surface), time, date, possible residual dive time at this depth or ambient pressure depending on the present estimated state of saturation of the user's body and its residual quantity of gas respiratory and possibly the request it expressed via the data entry means in terms of maximum duration of the dive, maximum depth or ambient pressure reached during this dive, current depth or ambient pressure, ascent rate current, residual amount of respiratory gas present (pressure P or equivalent volume for a given ambient pressure which may be the pressure prevailing on the surface), residual quantity of respiratory gas predicted at the end of the ascent prescribed by the device, pulmonary ventilation, oxygen consumption, user's cardiac output, ambient temperature, all information may have been stored by the user via the data entry means, answer to the question "has the maximum admissible depth (which may have been defined by the user) been exceeded?", answer to the question " has the maximum dive time (which may have been defined by the user) been exceeded? ", answer to the question" Has the maximum dive time been exceeded after the ascent prescribed by the device? " answer to the question "does the residual quantity of respiratory gas allow to go up according to the indications of the device (taking into account a safety threshold which may have been defined by the user)?", answer to the question "the maximum speed is the allowable ascent exceeded? ", answer to the question" is the current depth less than that of the first bearing to be performed? ", answer to the question" is the current depth less than the minimum allowable depth of the continuous decompression? "answer to the question" charging status means SUPPLY TERMINAL tat ⁱ on electrical energy is satisfactory? ".

The sound means comprise one or more electro-acoustic transducers adapted to the ambient environment (for example hydrophones in a marine or fresh water environment) as well as their associated generator and amplifier circuits. These transducers are electromagnetic or piezoelectric, monotone or multitone, capable of informing the user in a qualitative way (alarms and signals-differentiated or not according to the information transmitted, particularly suitable for information of binary type), or even quantitative for example by speech synthesis if they are associated with one or more speech synthesis circuits receiving their instructions from the calculation means, the information transmitted by said sound means can be any combination of those listed above with reference to the means visuals.

Tactile means are made up of mechanical appendages driven by electromagnets or electric motors. These mechanical appendages come into contact with any part of the user's body or fixed electrodes in permanent contact with the user's skin. These electrodes cause a slight discharge.

Said tactile means if present allow, in the event of important information to be transmitted to the user (see list referring to visual means), to draw his attention to said visual means even under ambient noise conditions which would make ineffective sound means.

The present invention also relates to a diving set comprising, in addition to a device according to the invention, a breathing apparatus composed of reserves of compressed gases carried or not carried by the diver, one or more regulators, and possibly a breathing bag provided with valves and a carbon dioxide absorption cartridge and an automatic oxygen dosing device, possibly a waterproof lamp, possibly orientation instruments (compass, goniometer), a diving mask or helmet, possibly means of propulsion (fins, underwater "scooter"), possibly means of protection against the cold (heated suit or not), possibly means of adjusting the buoyancy of the diver and his equipment (lifeline, ballasts or dry suit) with or without a supply of inflation gas independent of the supply of respiratory gas, possibly a turret or box or cha m decompression bre. It may include a turbine-electric generator assembly (dynamo or rectified alternator) associated with a regulator and capable of extracting the energy for expansion of the respiratory gases and / or inflation of the means for adjusting the buoyancy and to maintain in a state of load satisfying the means of supplying electrical energy to the assembly during the dive. Said device according to the invention can be incorporated into the diving helmet and can comprise a corrective optical assembly based on lenses and / or mirrors and / or prisms and / or semi-reflecting blades allowing close-up vision, and possibly superimposed in the normal field of vision, visual means of indication. This device can also include conventional sound indication means (speakers, headphones) operating in the gaseous volume of the headset, and can include voice type data input means consisting of a microphone or laryngophone connected to the means of calculation via a speech recognition module. The diving assembly can include two solenoid valves controlled by the calculation means, binary way via relays or switches known as "solid-state" or proportionally via digital-analog converters followed by amplifiers, one controlling the entry of the inflation gas into the jacket or dry suit and the other controlling the escape of said gas to the ambient environment, said solenoid valves allowing said means of calculation as a function of time, ambient pressure and possibly its time derivatives - easily calculated as a function of the output signals over a period of time of the time measurement means and of the ambient pressure measurement means -, possibly of information previously stored in memory by the user via the input means data (such as the diver's mass, its volume, its coefficient of resistance to movement in water, the compressibility coefficient and the e volume at the surface of his suit) and possibly the current decompression program, to stabilize the diver at a given depth (at the diver's request via the data entry means) or at all depths, to make him perform an ascent " in disaster "or at controlled speed (after possible warning, via the diver's means of indication, leaving the latter the option of aborting the procedure via the data entry means or by simply disconnecting the solenoid valves) in case detection of an emergency condition (for example a drowning made probable by apnea - zero ventilatory flow - of abnormally long duration, or an abnormally high ambient pressure making it probable a state of narcosis in the diver) or to make him execute continuous ascent or in steps prescribed by the device (at the diver's request via the data entry means).

The calculation means of said device according to the invention may be able to similarly control a solenoid valve responsible for the decompression of a diving turret or chamber or decompression chamber and possibly another responsible for its compression, thus automating the operation of said turret or box or chamber as regards decompression and possibly as regards compression.

A preferred embodiment among the combinations of embodiments given for each of the main components of the device, particularly suitable for the use of scuba divers, and which has the advantages of being economical, versatile and relatively simple, is as follows :

The ambient and reservoir pressures are transmitted to the "pressure" inputs, mouthed on one side of the housing, of two absolute pressure sensors, monolithic (with single semiconductor substrate) of the "Wheatstone bridge" type whose measurable pressure ranges are compatible to their respective measurands, via a rot-proof stainless membrane and an incompressible, non-corrosive and electrically non-conductive intermediate fluid in both cases, also via a flexible hose designed for high pressures (armed) connected to the HP outlet of the regulator in the second case.

The two bridges are excited by constant voltages obtained by amplification of the constant voltage output of the single voltage-frequency converter ("ratiometric" arrangement), on the voltage input to be measured "from which the signals are multiplexed, after amplification and offset. of said bridges as well as the "temperature" output with which said converter is also provided.

The means of calculating and measuring time, consisting of an 8-bit CMOS microcomputer in a box (microprocessor, read-only memory, random access memory, 16-bit timer or timer, 29 input-output lines), control multiplexing analog signals to be measured by two of their input-output lines, and receive the output frequency of the converter on their frequency line to be measured. They are therefore able to know at any time the uncalibrated values of the ambient pressure, the tank pressure and the temperature, to calibrate them and, as regards the pressures, to apply thermal compensations to them. The calibration and thermal compensation constants are introduced into the microcomputer's RAM thanks to data input means of the "reed" type controlling the state of input-output lines of said microcomputer. This manipulation does not need to be repeated each time the device is started, but can be repeated at annual intervals if a deterioration in the accuracy of the device was observed. The constants stored in the RAM survive indeed the periods of shutdown of the device and even the total discharge of the main batteries (cadmium-nickel), "sintered cells", 5 x 1.2 V 0.5 Ah) thanks to the auto passage matic in "Standby" mode (consumption of a few microamps, RAM saved) of the microcomputer when the device is stopped or when an appropriate device detects an advanced state of discharge of the main batteries, as well as using a back-up battery (cadmium nickel, "mass plate", 3 x 1.2 V, 0.1 Ah) with low self-discharge losses intended to take over in the event of exhaustion main batteries as regards exclusively the supply of the microcomputer in Standby and its satellites which are essential in this mode, which it can provide for several months. The rest of the time, ie when the main batteries are charged, they maintain the said back-up battery by 0.25 mA trickle charging. On the other hand, the device is provided with a second charge level detector for the main batteries, constituted like the first with a potential divider and a threshold detector, which changes the state of a line of microcomputer input-output when said charge level only allows a few hours of operation, so that the user is notified.

• a) Il permet l'usage de capteurs de pression non calibrés et non thermiquement compensés, donc bon marché.
• b) Il permet une calibration sans manipulation délicate de potentiomètres ou autres composants variables et même sans ouverture du boîtier du dispositif, par simple lecture des indications de l'appareil soumis à des pressions et températures connues et introduction de constantes aisément calculées à partir desdites indications et desdites valeurs connues.
• c) Il assure une calibration/compensation précise parce qu'en aval de tous les circuits analogiques.
• d) Il autorise des recalibrations aussi fréquentes que nécessaires, pouvant être effectuées éventuellement par l'utilisateur lui-même.
• e) Il permet l'affichage de la température de l'eau au bénéfice du plongeur.
• f) Il permet l'entrée d'autres constantes telles que pression en surface, composition du mélange respiratoire etc.... qui seront également préservées lors de l'arrêt ou de la décharge du dispositif.

This arrangement is advantageous for several reasons:

• a) It allows the use of non-calibrated and not thermally compensated pressure sensors, therefore inexpensive.
• b) It allows calibration without delicate manipulation of potentiometers or other variable components and even without opening the device housing, by simply reading the indications of the device subjected to known pressures and temperatures and introduction of constants easily calculated from said indications and said known values.
• c) It provides precise calibration / compensation because downstream of all analog circuits.
• d) It authorizes recalibrations as frequent as necessary, which can possibly be carried out by the user himself.
• e) It allows the display of the water temperature for the benefit of the diver.
• f) It allows the entry of other constants such as surface pressure, composition of the respiratory mixture, etc., which will also be preserved when the device is stopped or discharged.

The main batteries are simply charged via two bare stainless steel contacts emerging from the housing, the discharge of said batteries by the same path being prevented by the interposition of a diode. This diode can be short-circuited by an reed switch controlled from the outside, allowing rapid total discharge of the main batteries in an emergency via the external contacts, a condition necessary for the subsequent execution of a rapid total charge at 2 A in 15 minutes without danger for the batteries. Upstream of this diode, that is to say between the diode and the external positive contact, a second diode connected to the positive pole of the "back-up" battery via a resistor, performs a 1 mA bypass of the current charging, allowing a relatively quick recharging of said back-up battery when it has been used for a prolonged period, which the trickie charging current cannot guarantee. The maximum permanent charging current of the together is 68 mA.

There are two types of indication: visual and audible. The visual means consist of a transflect ⁱ f LCD screen module (lighting either behind or in front) with 32 alphanumeric characters multiplexed, in a resistance scale associated with an analog multiplexer allowing the adjustment of the optimal reading angle of the the screen by that of the excitation voltage of the liquid crystals, into an electroluminescent panel underlying the screen and into a wave generator intended to supply said panel. The calculation means control said visual means by fifteen of their input-output lines: eleven are dedicated to data transmissions, three to control the multiplexer 8-1, one to the wave generator of the EL panel controlled via a Darlington .

The audible indication means consist of a piezoelectric transducer connected to the "frequency output" line of the microcomputer via an amplifier.

• a) Meilleure précision dans la détermination de l'état de saturation de l'utilisateur, conduisent à l'établissement de programmes de décompression plus appropriés aux saturations réelles des tissus, donc généralement plus fiables que ceux prescrits par les dispositifs et procédés existants.
• b) Cette meilleure précision conduit dans de nombreux cas à un programme de décompression substantiellement plus court que celui obtenu par une autre méthode.
• c) L'économie de temps évoquée en (b) se traduit par une économie financière importante en ce qui concerne les compagnies de travaux hyperbares autorisant l'exécution d'une tâche donnée à moindre coût.
• d) Le dispositif mesure et affiche le temps de plongée, la pression ambiante, la pression bouteille, la température ambiante.
• e) Le dispositif prend à sa charge tous les calculs relatifs à la décompression de l'utilisateur, allant jusqu'à la détermination du moment où cette décompressiondevrait commencer en fonction de la quantité résiduelle de gaz respiratoires.
• f) Le programme de décompression est évolutif, c'est-à-dire que même en cours de décompression, le programme qui reste à effectuer s'adapte aux conditions dans lesquelles la décompression a réellement été effectuée jusqu'à ce moment. Cette adaptabilité peut même aller jusqu'à l'application de la règle thérapeutique de la demi-pression ou celle de la demi-profondeur en cas de violation importante des contraintes de décompression, ladite application ne présentant aucune difficulté du point de vue logiciel.
• g) Bonnes communications du dispositif vers le plongeur grâce à des moyens d'indication s'adressant à plusieurs des sens du plongeur. Bonne lisibilité des moyens visuels quelle que soit la lumière ambiante. Flexibilité de l'affichage sur écran, autorisant, outre l'affichage routinier de paramètres numériques relatifs à l'exposition et à la décompression, l'affichage occasionnel de messages alphanumériques explicites (avertissements, alarmes, rappels) accompagnés d'un signal sonore.
• h) Souplesse de calibration, compensation thermique, adaptation à de nouvelles conditions de plongée (pression de surface, composition du mélange respiratoire, etc...) et possibilité de personnalisation du dispositif (constantes définissant la relation ventilation pulmo- naire/débit cardiaque/pression, tensions de contrôle, etc...) grâce aux moyens d'entrée de données.
• i) Le dispositif convient tant aux professionnels qu'aux plongeurs d'exploration grâce à sa méthode de calcul qui tient compte du travail effectué au fond.
• j) Fiabilité technique et longue durée de vie du dispositif, grâce à la possibilité de sceller le boitier en usine en atmosphère inerte, due à la facilité de charge extérieure des batteries.
• k) Faible consommation électrique, permettant le fonctionnement continu du dispositif sur ses réserves énergétiques pendant plusieurs jours et le calcul de désaturation des tissus pendant les intervalles de surface.
• 1) Avertissement de l'utilisateur plusieurs heures avant la décharge totale des batteries principales.
• m) Batterie de back-up assurant la sauvegarde des constantes de calcul dans toutes circonstances (sauf abandon du dispositif pendant plusieurs mois sans le recharger, au quel cas une ré-initialisation des constantes est nécessaire; cette circonstance sera de toute façon détectée par le dispositif et signalée à l'utilisateur).
• n) Recharge indéfinie (après 10 h les batteries principales sont entièrement rechargées mais une prolongation indéfinie de la durée de charge ne les met pas en danger) ou rapide (15 mn, une décharge préalable étant nécessaire et rendue possible par l'interrupteur by- passant la diode de charge, une prolongation de la durée de charge risquant d'endommager les batteries) au choix de l'utilisateur et selon l'urgence de la situation. Un dispositif automatique relativement simple peut assurer la charge à courant constant des batteries dans l'un ou l'autre de ces deux modes (y compris le déclenchement à distance de l'interrupteur reed de by-pass par création d'un champ magnétique le long du reed à l'aide d'une bobine parcourue par un courant, y compris également la décharge préalable à la charge rapide à l'aide d'un dispositif de commutation et de détection de seuil) en toute sécurité, la temporisation de la charge rapide pouvant se faire à l'aide d'un simple timer. Un tel dispositif automatique de charge peut être conçu de façon à fonctionner indifféremment à partir d'une alimentation secteur ou d'une batterie de véhicule de 12 ou 24 V.

In conclusion, here are the advantages of a device such as the one whose realization has just been described, applying the methods of calculation of the decompression program described above, compared to one or the other (all, in this which concerns at least a, b and c) existing or already proposed devices and processes:

• a) Better precision in determining the state of saturation of the user, lead to the establishment of decompression programs more appropriate to the real saturations of the tissues, therefore generally more reliable than those prescribed by the existing devices and processes.
• b) This better precision leads in many cases to a decompression program substantially shorter than that obtained by another method.
• c) The saving of time mentioned in (b) translates into a significant financial saving with regard to the hyperbaric works companies authorizing the execution of a given task at lower cost.
• d) The device measures and displays the dive time, the ambient pressure, the tank pressure, the ambient temperature.
• e) The device takes care of all the calculations relating to the decompression of the user, going until the determination of the moment when this decompression should start according to the residual quantity of respiratory gases.
• f) The decompression program is evolving, that is to say that even during decompression, the program which remains to be carried out adapts to the conditions in which the decompression was actually carried out up to this time. This adaptability can even go as far as applying the therapeutic rule of half-pressure or that of half-depth in the event of a significant violation of the decompression constraints, said application presenting no difficulty from the software point of view.
• g) Good communications from the device to the diver by means of indication addressing several of the diver's senses. Good readability of visual aids whatever the ambient light. Flexible display on screen, allowing, in addition to the routine display of digital parameters relating to exposure and decompression, the occasional display of explicit alphanumeric messages (warnings, alarms, reminders) accompanied by an audible signal.
• h) Flexible calibration, thermal compensation, adaptation to new diving conditions (surface pressure, composition of the respiratory mixture, etc.) and possibility of customizing the device (constants defining the pulmonary ventilation / cardiac output / relationship) pressure, control voltages, etc.) by means of data entry.
• i) The device is suitable for both professionals and explorers thanks to its calculation method which takes into account the work done at the bottom.
• j) Technical reliability and long service life of the device, thanks to the possibility of sealing the case in the factory in an inert atmosphere, due to the ease of external charging of the batteries.
• k) Low power consumption, allowing the continuous operation of the device on its energy reserves for several days and the calculation of tissue desaturation during surface intervals.
• 1) User warning several hours before the total discharge of the main batteries.
• m) Back-up battery ensuring the backup of the calculation constants in all circumstances (except abandonment of the device for several months without recharging it, in which case a reinitialization of the constants is necessary; this circumstance will in any case be detected by the device and reported to the user).
• n) Indefinite charging (after 10 a.m. the main batteries are fully charged but an indefinite extension of the charging time does not endanger them) or rapid (15 min, a prior discharge being necessary and made possible by the by- passing the charging diode, an extension of the charging time may damage the batteries) at the option of the user and depending on the urgency of the situation. A relatively simple automatic device can ensure constant current charging of the batteries in either of these two modes (including the remote triggering of the reed bypass switch by creating a magnetic field the along the reed using a coil traversed by a current, including also the discharge prior to rapid charging using a switching and threshold detection device) safely, the timing of the quick charge that can be done using a simple timer. Such an automatic charging device can be designed to operate indifferently from a mains supply or from a 12 or 24 V vehicle battery.

Claims (10)

1. Procedure for real-time determination of the decompression of a diver or a worker under high pressure conditions, according to which the following parameters are measured during exposure:

- time (t),

- ambient temperature (^T),

- ambient pressure (o),

- pressure of a breathing air tank (P), with a mixture containing a neutral gas such as nitrogen. This process is characterised by the fact that it consists in:

1: Calculating the lung ventilations (V'E), by applying a gas distension law such as, for example:

in which

V is the volume of the breathing air tank containing the defined mixture,

P is the ambient pressure,

dp is the breathing tank pressure variation between two successive readings,

dt is the time interval between two successive readings,

2: Determining the maximum heart blood-flow values (Q'C) which correspond to the the lung ventilations (V'E), using predefined empirical tables obtained during experiments on several subjects at different ambient pressures.

3: Calculating the quantities (qi) of neutral gases dissolved, or of gasses contained in one or several theoretical body tissues (i), making up a mathematical model of the divers organism, by applying an elapsed real-time integration of the gas exchange rates (dqi/dt) of the theoretical body tissues; based on the following relationship

in which:

qi is the quantity of neutral gas present in the

corresponding body tissue (i), Ai is equal to:

either (gp-qi) if qi < (p+Ki), i.e. if there are no bubbles in body tissue (i):

or (gp- (p+Ki)) if qi > (p+Ki), i.e. if bubbles are present in body tissue (i).

g is the molar fraction of the neutral gas in the breathing air mixture;

Ki > 0 is a pre-established constant defined by experimentation representing the bubble formation threshold in body tissue (i),

ki is the time coefficient of body tissue (i), which can be calculated as follows:

ki - ai,1Qc + ai,0 where ai,1 > 0 if Ai > 0, i.e. an increasing function of the heart blood-flow in the case or absorption of the neutral gas by the body tissue.

or ki - βi,1 T + βi,0, where βi,1 > 0 if Ai > 0, i.e. an increasing function of temperature in the case of elimination of neutral gas by the body, tissue.

ai,1 > 0, ai,1 > 0 and βi,1 > 0 and βi,0 are predefined constants obtained by experimentation for a body tissue (i).

4: Calculating, by future-time integration of equation (1), assuming that Qc and T will retain their values, the future evolution of each (qi) corresponding to a body tissue (i), in the case of a hypothetical rise-to-surface from the current ambient pressure (p) at a normally used constant speed (for example 10 to 20 m/mn), until (qi) of any given body tissue reaches a maximum allowable value of (qi)max.

5: Calculating the depth at which the (qi) of a given body tissue will reach a maximum allowable value (qi)max, where (qi)max is a predefined empirical function of the body tissue and the depth, and determining the first static depth level as that at which the depth is equal to or just greater than the said calculated depth.

6: Calculating the time that must be spent at the depth of sustained level (D1) so that the (qi) values of all body tissues (i) are less than or equal to the (qi)max values of the next sustained depth level, after which the diver can rise to the next sustained depth level in a short time.

7: Repeating step (6) until the diver reaches the surface.

2. Procedure according to requirement (1), which is characterised by the fact that it consists in:

- storing the highest calculated lung ventilation value (V'E) max,

- storing the highest ambient pressure measured, and deducing the maximum depth reached,

- storing the lowest measured temperature (T)min,

- selecting a working decompression table, such as the French Ministry of Work table, if (V'E)max is greater than a recorded lung ventilation value, or if (T)min is less than a recorded temperature value.

- selecting an exploration decompression table, such as the GERS table (French Navy), if (V'E)max is less than the said recorded lung ventilation value, and if (T)min is greater than the said recorded temperature value,

- extracting, from the selected table, the decompression schedule which corresponds to the maximum depth reached and the measured time under water (t).

3. Procedure according to requirement (2), which is characterised by the fact that:

- the recorded lung ventilation value is 40 litres/min, and

- the recorded temperature value is 10°C.

4. Automatic device to calculate and indicate an optimum decompression schedule according to the procedure defined by requirements R1 to R3 characterised by the fact that it includes:

1: A device to measure time (t), which generates signals representative of this time value,

2: A device to measure ambient temperature (T), which generates signals representative of this temperature value,

3: A device to measure ambient pressure (p), which generates signals representative of this pressure value,

4: A device to measure the breathing air tank pressure (p), which generates signals representative of this pressure value,

5: Data input devices, enabling the volume of breathing air to be input, as well as the choice of either method for calculating the decompression schedule.

6: Memory-based data processing devices into which the measuring device output signals and data input device signals are input. These devices shall:

a) calculate lung ventilation (V'E),

b) choose which of two prerecorded decompression tables should be used, after comparing the calculated maximum ventilation value with a prerecorded ventilation value, and the calculated minimum temperature value with a prerecorded temperature value, and using the selected table to define the decompression schedule which corresponds to the measured time under water and the measured maximum depth, or calculate by elapsed time and future time integration, the concentration values of neutral gas in the different body tissues, and use this to establish the decompression schedule,

c) generate output signals which are representative of the calculated decompression schedule,

7: Indication devices which receive the calculating device output signals.

5. Device according to requirement 4, characterised by the fact that its pressure measurement devices and calculation devices for various calculations including lung ventilation, are made up of:

- a breathing air tank pressure (P) sensor, connected to this tank by a flexible pipe, generating a signal which is representative of the said pressure,

- an ambient pressure (p) sensor, with a noncritical location, generating a signal which is representative of the said pressure,

- a multiplexer, with certain inputs connected to the breathing air tank pressure sensor output and to the ambient pressure sensor output, whose output sends these signals sequentially, in a repetitive cycle, to an analog-to-digital converter,

- an analog-to-digital converter, whose input is connected to the multiplexor output, and whose output is connected to a microprocessor,

- a microprocessor which receives, from the analog-to-digital converter, successive pressure values measured at predetermined intervals this microprocessor then calculates the lung ventilation.

6. Device according to requirement 4, characterised by the fact that the memories of the memory based automatic calculation devices comprise data representative of the data in the GERS table (French Navy) and of the French Ministry of Work table, or of any other table.

7. Device according to requirement 4, characterised by the fact that the memories of the memory based calculation devices contain data from a real-time and future-time calculation program for the quantities of neutral gas present in the theoretical body tissues.

8. Device according to requirements 4 and 6, characterised by the fact that it comprises registers, to receive and store the highest lung ventilation value, the lowest temperature value, the highest ambient pressure to which the diver is subjected, and the value of the time under water, and that it comprises calculation devices, which use the minimum ambient temperature and the lung ventilation value stored in the registers, and which select either the table or the French Ministry of Work table, and which subsequently use the highest ambient pressure value determining the maximum diving depth and the time under water, and which select the decompression schedule corresponding to the selected table.

9. Device according to requirement 4, characterised by the fact that it comprises two solenoid valves controlled by calculation devices, the input of one being connected to a gas tank other than the breathing air tank, and its output being connected to an inflatable jacket or equivalent, and the input of the other being connected to the inflatable jacket and its output open to ambient; the calculation devices control either of the valves in order to inflate or deflate the jacket and generate an automatic rise to the surface, this rise to surface being initiated either automatically, due to an anomaly, according to prerecorded instructions, or by a deliberate order given by the operator.

10. Diving system characterised by the fact that it comprises a device per requirements 4 to 9, considered individually or collectively.

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