DE10253935B3 - Controlling pressure delivered by continuous positive airway pressure device involves slow, quasi-ramp-shaped reduction of pressure delivered by device as long as there is no respiratory event - Google Patents

Abstract

The method involves repeated measurement of a flow of breath during the operation of the continuous positive airway pressure or CPAP device and determining at least one respiratory event from the measured time variation. A respiratory event represents an indication that the pressure from the CPAP device is too low. It involves slow, quasi-ramp-shaped reduction of the pressure delivered by the device as long as there is no respiratory event. The method involves repeated measurement of a flow of breath during the operation of the continuous positive airway pressure device (1) and determining at least one respiratory event from the measured time variation of the flow of breath, whereby a respiratory event represents an indication that the pressure from the continuous positive airway pressure device is too low. It involves slow, quasi-ramp-shaped reduction of the pressure delivered by the device as long as there is no respiratory event. Independent claims are also included for the following: (a) a device for carrying out continuous positive airway pressure therapy (b) and a memory medium for use with a continuous positive airway pressure device.

Description

This invention relates to a method for controlling the pressure supplied by a CPAP device according to the preamble of claim 1, a CPAP apparatus for performing a such method and a corresponding storage medium. In particular The invention relates to a method in which the pressure in dependence of respiratory events.

Devices are known for performing the CPAP (continuous positive airway pressure) therapy. The CPAP therapy is in Chest. Volume No. 110, pages 1077-1088, October 1996 and Sleep, Volume No. 19, pages 184-188. A CPAP device applies by means of a compressor, preferably via a humidifier, via a hose and a nasal mask a positive overpressure up to about 30 mbar in the respiratory tract of the patient. This overpressure is intended to ensure that the upper respiratory tract remains fully open throughout the night and thus no obstructive respiratory disorders (apnea) occur ( DE 198 49 571 A1 ).

1 shows CPAP device 1 and a patient 19 , The CPAP device in turn includes a compressor 4 , a breathing tube 9 , a respiratory mask 18 , a pressure sensor 11 as well as a flow sensor 16 , To generate an overpressure, the compressor includes a turbine B. The turbine is also referred to as fan, fan unit, compressor, fan or blower. These terms are used synonymously in this patent. The illustrated CPAP device contains the pressure sensor 11 in the compressor housing and measures the pressure generated by the turbine. The pressure gauge can be connected to the respiratory mask via a hose and thus measure the pressure in the respiratory mask. Finally, the pressure sensor can also be located in the respiratory mask and be connected to the compressor housing via electrical lines. In or near the mask are one or more small holes 2 attached so that on average over time an air flow from the compressor to the holes 2 arises. This prevents the accumulation of CO ₂ in the breathing tube 9 and allows the patient to be supplied with oxygen.

The speed of the turbine 8th is through a microcontroller 5 so regulated that with the pressure sensor 11 measured actual pressure coincides with a predetermined target pressure. The target pressure is conventionally preset under the supervision of a physician and referred to as titration pressure. The flow sensor can, for. B. a sensor with heating wire 17 his. In another design of the CPAP device, a restriction in the breathing tube may be provided for the respiratory flow measurement, whereby the differential pressure across the constriction is measured. The pressure sensors can be arranged directly in the breathing tube or connected to it via further pressure measuring hoses. The microcontroller 5 can also take over the pressure control.

It turned out that patients from the CPAP device generated overpressure as an unpleasant resistance against which they had to exhale. Therefore, control methods for CPAP devices have been developed which set the target pressure as far as possible Lower. Such control is known from WO00 / 24446. This control is based on an algorithm in which during an "Autoset" operation successively at least three pressure values are set. Is the tidal volume independently from the set pressures, Such were the pressures too high. If the tidal volume increases with the set pressures, Such were the pressures too low.

To reduce the perceived overpressure, BiPAP devices and multilevel devices have also been developed. Such a device is in the DE 691 32 030 T2 described. The pressure is raised by a valve during inhalation and lowered during exhalation. The valve is controlled to maintain constant pressure during inhalation and exhalation. If the valve position changes only slowly during an inhalation process, this is interpreted as the end of the inhalation process. Inaudible vibrations or pressure changes can be evaluated to determine if the patient's breathing is regular, irregular or apneic. In addition, the duration of inhalation and exhalation and the flow rates can be determined. This information can be stored in memory. Finally, an admittance from respiratory flow divided by pressure can be calculated. The time course of the admittance can be compared with stored admittance schemes. The number of the most appropriate admittance scheme may be used as a "pointer" to a table containing the action to be taken, such as an increase in pressure.

WO 94/23780 describes a method for controlling the pressure of a CPAP device. If no respiratory disturbances occur during sleep, the pressure is gradually lowered. If sleep disorders such as apneas, hypopneas or snoring occur, the pressure is increased. The US 5,335,654 and the EP 0 934 723 A1 describe a similar procedure.

The EP 0 612 257 B1 also describes an auto-CPAP system that detects apneas, hypopneas, and unstable breathing to adjust the pressure.

Also, WO 99/24099 describes a Control procedure for an auto-CPAP device, considered apnea, hypopnea, decreased respiratory flow and snoring.

According to the US 5,740,795 the respiratory flow signal is fed to a band limited differentiator. If the output signal of the differentiator exceeds an inhalation threshold or falls below an exhalation threshold, an exhalation detection signal or a one-event detection signal is determined.

Also the EP 0 934 723 A1 relates to the control of a CPAP device due to the detection of apneas and partial occlusion of the upper respiratory tract.

In the DE 101 18 968 Further, a control method for CPAP devices is described. The DE 101 18 968 is incorporated by reference into this application. The control method first calculates characteristics from a measured respiratory flow curve and a measured actual pressure curve of a CPAP device. Special combinations of features are combined into detectors. Flags are set in the detectors when they detect an event, ie respond to the event. The control method then changes the target pressure based on the event flags of the detectors. The control method has three different states, namely a normal state, a sensitive state, and a leak state, between which it is possible to switch back and forth. Some detectors operate in the sensitive state with parameters deviating from the normal state. The control process changes to the sensitive state when the control process lowers pressure in the normal state. By choosing the parameters for the sensitive state, the control process responds faster if the actual CPAP pressure is too low. If, for example, the mask is disconnected, the controller changes to the leak state

The features include the expiration time, a backward correlation, a mean inspiratory volume, a mean curvature of the Respiratory flow during the inspiration as well as frequency from zero crossings in the Alternating part of the CPAP actual pressure.

In the transition from inspiration to Expiration can be seen in the respiratory flow a pronounced flank, which for the detection of single breaths is used. The local maxima of the first derivative correspond the maximum slope of the respiratory flow at the transition between inspiration and expiration. From the end of inspiration will be the beginning of Inspiration sought by following the first local minimum in the derivative is searched. The expiration time is a time difference between a minimum of the derivative and the previous maximum.

To calculate the backward correlation becomes the youngest Breath compared to previous breaths by calculating a cross-correlation function. The cross-correlation function has values between one and minus one, where the correlation is the same One becomes when the two breaths exactly match each other and equal to minus one when the curves are negatively correlated with each other, i. if a peak in the breathing pattern exactly coincides with a valley in the considered data piece. As backward correlation the mean becomes over a certain number of local maxima of the cross-correlation function designated before the current time.

To calculate the mean curvature of the Respiratory flow during the inspiration becomes the first derivative of the respiratory flow after the Time during appreciated the inspiration or calculated. Subsequently a line is fitted to the first derivative. The slope this adjusted straight line gives the mean curvature of Inspiration.

It has been shown that the number the zero crossings in the alternating part of the CPAP actual pressure a reliable feature for snoring is. The pressure control of a typical CPAP device is not so fast that she would be able to also snoring sounds auszuregeln. The zero crossings will only be during counted in the inspiratory phase, so that the controller responds only to inspiratory snoring. Also the variance of the actual pressure can be used to snore to detect.

According to the teaching of DE 101 18 968 From the features a respiratory arrest detector, an apnea detector, a hypopnea detector and a Atemflußlimitations detector are calculated as an indication of an increase in pressure and a normal detector as an indication of stable breathing and possible pressure reduction. In particular, the response of the respiratory arrest, apnea, hypnopnea and respiratory flow limitation detector are referred to below as respiratory events.

The respiratory arrest detector speaks if more than 2 minutes pass without detecting a breath. If this happens more than 3 times, the automatic pressure control breaks from.

The apnea detector first detects breaths, at which the expiration time is longer than 10 s and which are referred to as respiratory arrest. Of the Apnea detector speaks if either one of two successive apnea arrivals respiratory arrest longer lasts for 30 s or more than 3 consecutive respiratory arrest. Respiratory arrest are successively, if the duration of the intermediate hyperventilation block and respiratory period <60 s is.

For hypopnea detection, the non-normalized mean inspiratory volume, the backward correlation, and the snoring feature are used. Respiratory flow limitation detection uses the snoring feature, mean curvature, and backward correlation. For details of the hypopnea detector and the respiratory flow limiter detector is applied to the DE 101 18 968 directed.

For the detection of stable respiration, the normal detector uses the correlation feature. Stable breathing is when the set pressure for a given time z. B. 180 s was not changed and For example, during this time the backward correlation is ≥ 0.86.

In the prior art is also the Fuzzy logic known. According to the conventional Logic can logical variables only the states 0 or 1 - also referred to as "false" or "true" - accept. In fuzzy logic can Fuzzy variables Any value between 0 and 1 inclusive 0 and 1 accept. The fuzzy logic is used primarily in controllers used to consider the experience of professionals.

According to the fuzzy logic give fuzzy variables the affiliation to a lot. For a fuzzy controller, the quantity is the same a certain operating state of the device to be controlled. With the aid of fuzzy logic, it is possible to control under consideration to design a limited number of typical operating states. The fuzzy logic provides a formalism for interpolation between the considered ones States.

The object of the invention is to process for controlling the target pressure of a CPAP device, a CPAP device to carry out the procedure and a storage medium for a corresponding program, which allow it, based on the time course of the respiratory flow a patient for the Patients to set optimal CPAP target pressure.

This task is accomplished by the objects of independent claims solved.

Preferred developments of the invention are the subject of the dependent Claims.

The advantage of slowing down the pressure provided by the CPAP device is that the pressure is much finer than the pressure in DE 101 18 968 mentioned 1 mbar steps is adjustable. The set pressure will be more optimal, so better to meet the condition as low as possible but as high as necessary.

Advantageous to increase the Absolute value of the temporal pressure change rate is that of the CPAP device delivered pressure is lowered quickly, if he is still far above the optimal pressure is.

The occurrence of a respiratory Event indicates that from the CPAP device delivered pressure is already a bit too low. Under these circumstances is It is advantageous to quickly increase the pressure by a predetermined value, that is preferably stepwise to raise.

Has the CPAP device approximately the optimal Pressure reached, it lowers the set pressure, so to speak, on a trial basis ramp form to provoke a respiratory event. Will after the stepped Raising the pressure in about the pressure reached at the beginning of the ramp, this is an indication that the optimum pressure is about reaching has been. Under these circumstances It is beneficial to try the patient less frequently with a trial Lowering load and thus the time for keeping the pressure constant to extend.

Also avoiding a ramp at too low backward correlation advantageously does not help the patient in his sleep by provoking a respiratory event by test lowering the CPAP device disturbing pressure.

The following are preferred embodiments the invention explained with reference to the accompanying drawings. there demonstrate:

1 a CPAP device, and

2 a flowchart for explaining the method according to the invention.

2 explained with reference to a flow chart, the inventive method. It is essentially based on the ramp-shaped lowering of the target pressure in step 33.

The invention is the realization basis, that even with a slow change of the target pressure the above features, such as the Expirationszeit, in particular the Reverse correlation, a mean inspiratory volume and a mean curvature of the Respiratory flow with the time only insignificantly change, as long as the target pressure still over the optimal pressure, so long as there are no respiratory events occur. As the upper limit for the absolute value of the derivative the pressure after the time can be set 1 mbar per breath. Actually driven rate should be small compared this value, ie less than 0.2 mbar per breath.

To initialize the method, a value of two minutes is stored in step 31 in a memory called "normal time". Furthermore, the current target pressure is stored in step 32 in the memory "AlterDruck". Subsequently, the target pressure in step 33 is ramped down at a constant rate, ie the derivative of the target pressure after the time is constant. As mentioned above, the CPAP device is controlled by a microcontroller. In addition, that is from the pressure sensor 11 supplied signal digitized with a similar step size. The control of the turbine by the microcontroller takes place in fine digital steps. All this means that the target pressure is actually not ramped, but rather lowered in small steps. A ramped lowering is therefore to be understood for the purposes of this application, when the pressure is lowered in a quasi-ramp in several small steps within a breathing cycle. A respiratory cycle lasts about 4 to 5 s, so that after 1 sec, a small step should take place. In any case, the small steps should be small compared to 1 mbar, ie less than 0.2 mbar.

In step 34 it is checked whether a respiratory event has occurred. A respiratory event is the opposite of stable breathing, ie a respiratory disorder. In one embodiment, the in of the DE 101 18 968 described detectors with the exception of the normal detector, so in particular the apnea, hypopnea and Atemflußlimitationsdetektor be used. In other embodiments, the latter detectors can be used with other well-known in the art for the detection of respiratory disorders, such as those in the DE 691 32 030 T2 described admittance from respiratory flow divided by pressure or the mentioned in WO 99/24099 reduced respiratory flow and snoring are used.

As long as no respiratory event occurs, the target pressure in step 33 is further lowered. kick a respiratory event in step 34, the current Time in memory "StartTime" in step 35 to stored further use in step 41.

Subsequently, in step 36, the target pressure is increased stepwise by a predetermined value, for example by 1 mbar. The actual pressure follows the target pressure according to the inertia of the turbine 8th and the selected control parameters for the regulation of the actual pressure to the target pressure. A step-shaped lifting of the actual pressure delivered by the CPAP device should be understood to mean an increase which takes place within a breathing cycle, that is to say within 4 to 5 s. The reason for the step-like raising of the target pressure as fast as possible is that when a respiratory event occurs, the actual pressure is already too low for the current sleeping state of the patient. The too low pressure should be raised as quickly as possible in order not to disturb the sleep of the patient by further respiratory events.

After raising the set pressure in Step 36 becomes the target pressure with the value stored in the "age pressure" memory compared. In the memory "AlterDruck" was in step 32 the target pressure stored at the beginning of the ramp. Dodges the target pressure from the pressure stored in the memory "AlterDruck" By more than tolerance in step 37, this will be taken as an indication interpreted that the pressure at the beginning of the ramp near the optimal Pressure for the current sleep state of the patient was. In this case will the time stored in the "normal time" memory in Step 38 extended, to make the patient's sleep unnecessary by further respiratory To disturb events which are provoked by the lowering of the target pressure in step 33 test. The extension in step 38, by adding a constant value or multiplication with a value greater than 1 done.

After step 37 or 38 the set pressure is at least for the time stored in normal time memory kept constant. This condition is checked in step 41. In step 40 will be during the Keeping the set pressure constant will continue to check for respiratory events occur. If so, the target pressure in step 36 further increased, after the current time has been stored in the memory "start time" in step 35.

After it was determined in step 41, that since the time stored in the memory "start time" the time stored in normal time memory has passed, it is checked in step 42 whether the normal detector has addressed. As mentioned above, this can be the backward correlation be evaluated. Accordingly, there is a normal event when the backward correlation greater than a predetermined value, for example 0.86. In this way becomes when the breathing already starts to become uneven, so if the backward correlation falls below the predetermined threshold, waives by further lowering of the target pressure a respiratory event to provoke in step 34. Another normal detector is in the HEP17 (attorney 's reference HEP17, title "Procedure for a ventilator, respirator and Storage medium " Applicant: seleon gmbh).

This leads in an advantageous manner to a quieter, more restful sleep. Is the backward correlation sufficient? So, if a normal event is detected in step 42, it will become high after saving the current target pressure in the memory "AlterDruck" in step 32 again begun to lower the target pressure in step 33 until in step 34 a respiratory event is determined.

In another embodiment at step 33, the target pressure is not ramped at a constant rate, but with an increasing in absolute value over time Rate lowered. this leads to In addition, the setpoint pressure will reach the optimum pressure in a shorter time approaches, if the target pressure is initially well above the optimum pressure. For example, the rate can be proportional to that since the beginning of the Ramp past time rise, so for the target pressure a downwards opened Parabola results.

In a further embodiment The events detected by the detectors are called fuzzy variables treated. An advantage of this embodiment is that the controller works continuously. Preferably, the transition occurs from "no event" to "event occurred", ie the area in which the fuzzy variable increases from 0 to 1, such that the corresponding fuzzy variable reaches the value 0.5 at the limit specified above. One can considering of the gradual transition from 0 to 1 of fuzzy variables so formulate that, for example a more normal event is detected or detected the more clearly the backward correlation Threshold, for example, exceeds 0.86.

The width of the selected transition region and the course of the transition function are of secondary importance for the quality of the control process. For example, if the backward correlation is less than 0.82, the normal fuzzy variable may assume a value of zero if it increases linearly from 0 to 1, if the backward correlation falls within the range of 0.82 to 0.9, and equal to 1 if the backward correlation exceeds the value of 0.9. However, other functions such as a suitably scaled Arctan function or a probability integral Φ (x) may be used to design the transition region:

The rate of pressure change When using fuzzy variables, the sum of the values of the supplied with individual detectors and preferably with coefficients weighted fuzzy variables. At the coefficients becomes considered, that, for example, when a respiratory arrest is detected, the pressure increased quickly will, while For airflow limitation, the set pressure of the CPAP device is increased more slowly. Thus, for example, the coefficient for the apnea fuzzy variable becomes to be taller as the one for the Airflow Limitierungs fuzzy variable.

In a fuzzy embodiment of the invention, the absolute value of the rate at which the target pressure is lowered in step 33, lowered if one or more respiratory events are already recognized a little, so the fuzzy variables Have values in the range of 0.1 or 0.2. In this way the target pressure is lowered more slowly when the breathing is less becomes regular.

Also, the step height of raising the target pressure in step 36 can be made dependent on the fuzzy variables, with the the respiratory event has occurred. In one embodiment is ever a fuzzy variable for a specific respiratory event such as apnea or hypopnea occurred. In one embodiment depends on that increase the set pressure of the fuzzy variable with the highest Value decreases, so from the fuzzy variables, the most likely a respiratory Event signals. For example, does this variable have a value of 0.8, the target pressure is raised by 1 mbar. Does she have one Value of 0.9, the increase in the target pressure may be 1.1 mbar.

Also, for example, with the Lowering the target pressure to start at a very low rate, if the backward correlation approaches the value of 0.86 from below, so that the corresponding fuzzy variable is becoming more obvious a normal event announces. In another embodiment can also start with the lowering of the target pressure at a low rate when the time stored in the "normal time" memory not quite finished yet.

The above-described target pressure control method according to the invention can also with BiPAP devices and for multilevel devices be used. In this case, the determined by the control method Target pressure as the higher Printing on BiPAP devices or the highest Printing on multilevel devices be used. In another embodiment, the gives after one Control method according to the invention determined pressure the time average of a BiPAP or multilevel device generation pressures on.

A CPAP device can come with a slot 6 be equipped with a data line 10 with the microcontroller 5 connected is. In the slot 6 can be a storage medium 7 plugged in to another program in the microcontroller 5 save. In this way the firmware can be updated.

The invention has been described above of preferred embodiments explained in more detail. For a specialist However, it is obvious that various modifications and modifications can be made without departing from the spirit of the invention. Therefore, the scope of protection by the following claims and their equivalents established.

1

CPAP device

2

hole

4

compressor

5

microcontroller

6

slot

7

storage medium

8th

turbine

9

breathing tube

10

data line

11

pressure sensor

16

flow sensor

17

heating wire

18

breathing mask

19

Sleeping

31-42

steps

Claims (10)

Method for controlling the use of a CPAP device ( 1 ) with: repeatedly measuring a respiratory flow during operation of the CPAP device ( 1 ); and determining at least one respiratory event from the measured time course of the respiratory flow, wherein a respiratory event is an indication that the one of the CPAP device ( 1 ) supplied pressure is too low, characterized by slow, quasi ramped lowering ( 33 ) of the pressure delivered by the CPAP device, as long as no respiratory event is detected. Method according to claim 1, characterized in that the time derivative of the CPAP device delivered pressure during the slow, quasi ramped Lowering is constant. Method according to claim 1, characterized in that that the temporal. Derivation of the pressure supplied by the CPAP device during the slow, quasi ramped Lowering increases. Method according to one of the preceding claims, further comprising: lifting ( 36 ) of the pressure supplied by the CPAP device for the occurrence of a respiratory event. Method according to one of the preceding claims, further comprising: lifting ( 36 ) of the CPAP ( 1 ) delivered in a step by a predetermined value to the occurrence of a respiratory event; and keeping constant ( 39 ) of the CPAP device ( 1 ) supplied pressure during a predetermined time ( 41 ) after the respiratory event. The method of claim 5, further comprising: starting with the slow, quasi-continuous lowering ( 33 ) of the pressure supplied by the CPAP device if no respiratory event has been detected during the predetermined time; To compare ( 37 ) the pressure delivered by the CPAP, after an increase by the predetermined value, with the pressure at the beginning of the boost, preceding a slow, quasi-ramp, lowering of the pressure delivered by the CPAP device; Comparing the absolute value of this pressure difference with a threshold ( 37 ); and extend ( 38 ) of the predetermined time if the absolute value of the pressure difference is less than the threshold value. Method according to one of the above claims, which further comprising (42): determining the most recent respiratory cycle; To calculate a correlation value between the youngest respiratory cycle and this preceding breathing cycles; Averaging the correlation values; Determine, whether the mean over is a predetermined threshold; and Starting with the Slow, quasi-steady lowering of the CPAP device supplied pressure only if the threshold is not exceeded becomes. Method according to claim 5 or claim 6 or 7, insofar as they relate to claim 5, which stops keeping the pressure supplied by the CPAP device constant and raise the pressure when during the constantly holding the pressure detected a respiratory event becomes. device to carry out the CPAP therapy with a command memory and a central Processing unit that executes instructions stored in instruction memory, so the device to carry out the CPAP therapy A method according to any one of claims 1 to 8 performs. Storage medium for use with a CPAP device having a central processing unit for processing the in the storage medium stored commands, wherein the CPAP device at the Processing of stored in the storage medium commands a method according to claims 1 to 8 performs.