WO2011117241A1

WO2011117241A1 - Arrangement and method for non-invasive detection of haemodynamic parameters

Info

Publication number: WO2011117241A1
Application number: PCT/EP2011/054350
Authority: WO
Inventors: Jürgen Querengässer; Marcus Krellig; Olaf Solbrig
Original assignee: Medis. Medizinische Messtechnik Gmbh
Priority date: 2010-03-26
Filing date: 2011-03-22
Publication date: 2011-09-29
Also published as: DE102010016172A1

Abstract

The invention relates to an arrangement for non-invasive detection of haemodynamic parameters that are needed in particular to determine the cardiac stroke volume. The arrangement comprises at least two current electrodes (01, 02) and at least two measuring electrodes (03, 04) for placing on a patient's chest, and an evaluation and control unit (05), which contains means for realization of an impedance cardiography device for recording an impedance cardiography signal from which the left ventricular ejection time LVET_IKGand the time of opening of the aortic valve (B point) can be extracted. The arrangement further comprises an upper arm pressure cuff (06) and/or a thigh pressure cuff (08), which detect a pulsatile pressure change fed to the evaluation and control unit (05). The evaluation and control unit (05) determines, from the upper arm pressure signal, a left ventricular ejection time LVET_IKGand compares this with the left ventricular ejection time LVET_IKGor it determines an aortic pulse wave velocity, and it generates warning signals if the difference between LVET_P and LVET_IKG and/or the pulse wave velocity lie outside predefined tolerance ranges. The invention also relates to a method for non-invasive detection of haemodynamic parameters.

Description

Arrangement and method for noninvasive detection

hemodynamic parameter

The invention relates to an arrangement and a method for the continuous, noninvasive detection of hemodynamic

Parameters as they are particularly needed for determining the heartbeat ^¬ volume.

Impedance cardiography (IKG) is a well-known method for the non-invasive and continuous determination of heartbeat volume and other hemodynamic parameters (Kubicek WG, NASA CR

101965, 1969). It is based on measuring the impedance change across the thorax of a patient. This change is a measure of the volume of blood pumped from the heart into the arterial system, and especially the aorta. To determine the heartbeat volume, an empirically determined equation is used at the IKG, including the left ventricular expulsion time LVET _IKGr ie the time between the opening (B-point) and the closure (X-point) of the aortic valve, and the amplitude of impedance cardiographic

Signals dZ / dt _max must be determined. It is also described in the literature that it is possible to determine the left ventricular ejection time LVET with a tonometer on the carotid artery or on the axillary artery (Left Ventricular Ejection and the Heather Index Measured by Non-invasive Methods during Postural Changes in Man : DW Hill, AJ Merrifield, Acta Anaest. Scand 1976,

20, 313-320). In addition, devices are known (Tensiomed Arterio- graph), with which it is possible to derive a pressure pulse curve via a humeral cuff and from this, to determine the left ventricular expulsion time LVET _P. Due to the required blockade of the blood circulation, these methods can not be used or only with considerable burden for the patient in long-term measurements of the heartbeat volume.

One disadvantage of existing devices for performing impedance cardiography is that the X-point in the cardiac output signal, which is needed to determine the left ventricular ejection time LVET _IKG and correlates with the closure of the aortic valve, is reflected, for example, by reflected pulse waves and / or others in the venous system Volume changes is often not clearly pronounced and therefore can not or can not be determined correctly. This can lead to significant deviations in the circumstances

Determination of left ventricular ejection time LVET _IKG and thus lead to relevant errors in the calculation of the heartbeat volume.

In the use of impedance cardiography, in practice cases have repeatedly been observed in which the heartbeat volume determined by this method does not correspond to the actual conditions. This can be, for example, due to the fact that among other things the aorta Elah ^¬ ticity may be restricted by atherosclerotic changes and the associated stiffening of the vessels. As a result, with the same heartbeat volumes, there is a smaller change in volume in the thorax and, consequently, a smaller change in impedance, so that the amplitude of the measured impedance-cardiographic signal dZ / dt _{max is} reduced. In the result the heartbeat ^volume determined by means of impedance cardiography is underestimated.

Another disadvantage of the IKG is that any existing vascular changes and limitations of vascular elasticity are not detected and evaluated. As a result, it is not recognized that the measured amplitude of the impedance cardiac signal dZ / dt _max does not correctly reproduce the heartbeat volume, which likewise leads to errors in the calculation of the heartbeat volume.

US 2009/0259132 A1 describes a method and a device for determining the heartbeat volume by bioimpedance measurement on the upper arm of a patient using the pulsation in the arteries. In this context, it is proposed that

LVET from a pulse oximetry signal or its first Ablei ^¬ tion to determine. Alternatively, the LVET may be determined from an applanation tonometry signal or its first derivative. Due to the measurement of the upper arm, it is possible, in particular, for fault influences from diseased fluid deposits in the

Thorax can be reduced. For the user of the device described, however, it remains uncertain whether a patient should use the conventional method of impedance measurement at the thorax or the proposed measurement on the upper arm in order to obtain the safest results.

DE 10 2005 042 041 AI includes a method and a device for improving the diagnostic value of impedance cardiography (ICG). In addition to the ICG, the pulse wave velocity in the thoracic aorta is determined and evaluated at the same time. Depending on the size of the respective deviation of the determined pulse wave velocity from previously defined standard values, this deviation becomes in the determination of those determined on the basis of the IKG

Parameter taken into account and / or the user on the

diagnostic value of each determined parameters. In the solution described here becomes the

Determining the pulse wave velocity measured on the back. Here, the impedance plethysmography in which the electrical resistance is measured is used. Proble ^¬ cally in this method is that not only the aorta is detected by the measurement, but also obvious venous vessels, especially the large arteries of the kidneys, which are well supplied with blood and thus generate a large signal ^¬ component. This leads to a superposition of the arterial pulse wave in the aorta, which is supposed to be measured. The result signal is very sensitive to the electrode application and subject to strong fluctuations, which are in the range of physiological fluctuation of the useful signal, so this

Method not reliable and reproducible works.

An object of the invention is to provide a method and an arrangement which, in the context of conventional impedance cardiography, make it possible to obtain additional information which improves the accuracy of the determined left ventricular expulsion time LVET and the influence of a possibly reduced vascular elasticity to automatically detect the amplitude of the impedance cardiographic signal dZ / dt _max and to take into account in determining the heartbeat volume.

The object is achieved by an arrangement

Claim 1 and a method according to claim 4 solved. The arrangement according to the invention initially comprises a per se known impedance cardiography device in which at least two current electrodes and at least two measuring electrodes are applied to the thorax of a patient, wherein the measuring electrodes detect the body section to be examined and are always arranged between the current electrodes.

Moreover, the arrangement according to the invention zusätz ^¬ Lich to Impedanzkardiographiegerät Oberarmdruckman- comprises a cuff and / or a femoral pressure cuff and one or more associated transducer, which evaluate the brachial pressure pulse curve and / or the thigh pressure pulse curve.

The pressure pulse curve derived from an upper arm of the patient using the humeral cuff is passed through the

Transducer for the upper arm pressure pulse curve has been converted into an electrical signal and used to determine the left ventricular expulsion time LVET _P irrespective of the persistent cardiac impedance device.

In the calculation of stroke volume obtained both on the basis of impedance left ventricular ejection time LVET _IKG and the recovered from the upper arm ^¬ pressure pulse curve left ventricular ejection time LVETp be considered. Exist between the independently won

Values of the expulsion time more than deviations permitted within a predetermined time tolerance range, a first warning signal is generated, which indicates that the measured values supplied by the IKG are untrustworthy. In this case, the LVET _{IKG is} replaced by the LVET _P , since the latter is more trustworthy, and used, for example, for the calculation of the heartbeat volume. Within the pre-admit ^¬ nen tolerance may in a modified execution An average of LVET _IKG and LVET _{P is} formed and used to calculate the heartbeat volume.

The invention also makes use of the finding that, in the case of arteriosclerotic changes and associated stiffening of the vessels, not only a reduction in the amplitude of the measured impedance cardiographical signal dZ / dt _max , which can not be explained by classical ICG, occurs, but at the same time the aortic pulse wave velocity increases the value of the pulse wave velocity with the degree of

Vascular stiffness correlates.

Therefore, simultaneously or alternatively to the upper arm pressure cuff derived from a thigh of the patient with the aid of the thighs pressure cuff pressure pulse curve is converted by the transducer for the thighs pressure pulse waveform into an electrical signal and used to determine the central pulse wave velocity, the nachfol ^¬ neighborhood which also during validation gewon- by IKG nenen measured values and, if necessary, is taken into account in the calculation of Herzschlagvo ^¬ lumens. Is a lying outside a specified ^differently surrounded speed tolerance range ^¬ pulse wave velocity is detected, a second warning signal is generated which indicates that the measured values supplied by the ICG are not trusted. In this case, in particular, the amplitude values of the recorded impedance ^¬ cardiographic signal is erroneous, namely too low. To correct the amplitude values, a correction factor can be used as a function of the determined pulse wave velocity, which correction factor can be used, for example, by evaluating numerous

Measurement series can be determined empirically. The signaling of a pulse wave speed lying outside the specified tolerance range can in the simplest case be carried out by the user. but also be used to cause further examinations in the patient.

A significant advantage of the invention is that by including the upper arm pressure pulse curve a

additional possibility for determining the left ventricular expulsion time LVET _{P is} given, and thus the left ventricular determined on the basis of impedance cardiography

Exposure time LVET _{IKG can be} verified and, if necessary, corrected automatically, which leads to an increase in the accuracy of impedance cardiography.

Another advantage of the invention is that the aortic pulse wave velocity determined by inclusion of a femoral pressure cuff provides information about the aortic pulse wave velocity

Aortic elasticity provides on the basis of which can be estimated whether and, if so, to what extent the impedance cardiography must be corrected or discarded with regard to the determination of the heartbeat volume.

Further advantages and details of the invention will become apparent from the following description of a preferred embodiment, with reference to the drawings. 1 shows a basic representation of the components of an arrangement according to the invention and the positioning of sensors on the patient;

Fig. 2 is an illustration of waveforms that can be recorded with the inventive arrangement.

Fig. 1 illustrates both the components of a fiction, ^¬ arrangement and the positioning of several

Sensor on the patient. To determine the stroke volume of the heart by means of impedance cardiography (ICG) two or more current electrodes Ol, 02 are applied in a known manner to the thorax of the patient, via which a very low, high-frequency and constant alternating current is fed, which flows through the body section to be examined.

Between the current electrodes 01, 02, two or more measuring electrodes 03, 04 are arranged, with the help of a generic elekt ^¬ voltage can be measured, which varies depending on the pumped into the body during a cardiac stroke volume of blood. So change the blood volume in the investigation ^¬ section, so does its electrical impedance changes. The current and measuring electrodes can be different in number and size, as long as the basic principle of the measurement is maintained, after which the measuring electrodes 03, 04 always between the

Current electrodes 01, 02 are located and detect the body portion to be examined.

The arrangement has an evaluation and control unit 05, which initially comprises all conventional means for performing an impedance cardiography. The evaluation and control unit 05 supplies the measured current to the current electrodes 01, 02 and receives the recorded measurement data from the measuring electrodes 03, 04. As the opportunities to build a conventional ICG device are known to the expert, is a detail ^¬ profiled Description known components of the evaluation and control unit omitted.

Using the measurement arrangement described for impedance cardiography (IKG), the curves shown in Fig. 2 can be derived, wherein the curve (a) the measured impedance change ^¬ -dZ (as referred to IMP) and the curve (b) the first mathematical Derivative of the curve (a) thus represents -dZ / dt, which is referred to as ICG. For a better understanding, the chronologically associated course of the signal recorded by an electrocardiogram is also shown as curve (c). In the ICG curve (b) the following typical curve points can be determined, which are needed to determine the stroke volume of the heart:

B - opening the aortic valve,

X - closing the aortic valve and

C - maximum systolic flow,

wherein the time range between points B and X represents the left ventricular expulsion time LVET _IKG .

As already mentioned above, as a result of pathological changes in the vascular system of humans, the vascular elasticity can be greatly reduced. This has the consequence that the propagation speed of the pressure pulse ^¬ curve is greatly increased in the aorta and the reflected light from the Peri ^¬ ripherals pressure pulse curve again reaches the aorta and the heart already during early systole. As a result, there is a superposition of forward and backward pressure pulse curves in the aorta and consequently also a modulation of the volume changes in the aorta. This process can also be superimposed by processes in the venous system or by fluid accumulation in the thorax. As a result, the X-

Move the point in the IKG curve so that it no longer exactly reflects the closure of the aortic valve. If the X-point in the ICG is determined incorrectly, this has a direct influence on the determination of the left ventricular expulsion time LVET _IKG and consequently leads to a faulty one

Calculation of the stroke volume of the heart. To solve this methodical problem, an upper arm pressure cuff is plat ed ^¬ 06, which is filled with a predetermined pressure according to the invention on the upper arm of the patient. This produces a coupling to the brachial artery and transfers its pressure changes to the humeral cuff 06.

The pressure changes detected by the upper arm pressure cuff are converted into an electrical signal with the aid of a first measuring transducer 07 and delivered to the evaluation and control unit 05. The signal delivered by the first transducer represents a humeral pressure pulse curve which, unlike the IKG signal delivered by the measuring electrodes 03, 04, is only to a small extent influenced by reflected pressure pulse curves and not by venous processes or fluid collections in the thorax. This provides a second possibility for determining the aortic valve closure and consequently also the left-ventricular expulsion time LVET _P , which in the case of pathological changes in the vascular system in any case yields different, mostly also more accurate values than the LVETIKG derived from the thorax.

Due to the evaluation and control unit 05 is determined from the brachial pressure pulse curve left ventricular Austrei ^¬ bung time LVETp is vergli ^¬ chen at regular intervals or when a given occasion with the determined left-ventricular ejection time curve from the impedanzkardiographischen LVET _ICG. If both values deviate from each other by more than a predetermined time tolerance, a first warning signal is generated, which indicates that the measured values supplied by the IKG are not trustworthy. Through the first warning signal can be preferably causes then that determined from the left ventricular pressure pulse curve Austreibungs ^¬ time LVETp for determining the stroke volume of the heart is pulled ^¬ zoom. In this way, an impedance cardiogram phical signal faulty certain left ventricular

Exposure time LVET _IKG can be detected and corrected if desired, increasing the reliability and accuracy of determining heartbeat volume.

As a rule, the continuous determination of the left ventricular expelling time continues to be based on the signal recorded by the ICG device integrated in the arrangement according to the invention, so that long-term measurements without significant impairment of the blood circulation in the

Upper arm of the patient can be performed.

For a preferred embodiment of the invention, it is important that, in the case of a heart contraction, the stroke volume of the heart is pumped into the aorta, which initially receives the blood volume on account of its wind-bowl function and then forwards it to the vascular system. This heart rate-related increase in the blood volume in the aorta leads to a corresponding change in the impedance of the thorax, which is used in impedance cardiography to determine the stroke volume of the thoracic aorta

Heart is evaluated. The blood volume taken up by the aorta in this case is reflected in particular in the C-point (dZ / dt _max ) of the impedance cardiographical signal. A reduced elasticity of the aorta can also lead to a

Cause reduction of the windkessel function of the aorta, with the same stroke volume of the heart entspre ^¬ sponding increase in the volume is reduced in the aorta in the result, leading to a reduction of the C-point (dZ / dt _max) cardiographic in the impedance signal and, consequently, underestimate the heartbeat volume based on impedance cardiography. Under these conditions, however, the pulse wave speed increased. This means that the pulse wavy ^¬ speed correlates with the elasticity of the vessels.

To determine the pulse wave velocity in the aorta, the thigh of the patient upper leg ^¬ pressure cuff 08 is placed according to the invention, which coincided with a vorbe ^¬ pressure is occupied. This produces a coupling to the femoral artery and transfers its pressure changes to the femoral pressure cuff 08. The thigh cuff pressure from the top 08 recorded changes in pressure are converted using a second transducer 09 into an electrical ^¬ signals are available and supplied to the evaluation and control unit 05th The thus obtained femoral pressure pulse curve allows a clear determination of the time at which the pulse curve has reached the thigh pressure cuff 08. At the same time the B-point, ie the time of the aortic valve opening, is determined in the impedance cardiographic signal. The Zeitdif- ference between the moment of Aortenklappenöffnung (B-point) and the time at which the pressure wave has the thigh ^¬ pressure cuff reaches 08, defines the propagation ^¬ time of the pulse wave. Referring pressure cuff this time to the distance between the aortic valve and the position of the thigh, one obtains the aortic Pulswellengeschwin ^¬ speed, which in turn profiled ^¬ with the elasticity of the aorta korre. Provided that the pulse wave velocity is determined except ^¬ half a predetermined speed tolerance range, a second warning signal is generated which indicates that the measured values supplied by the ICG are not trusted. In this case, in particular, the amplitude values of the impedance cardiographical signal are erroneous. If an automatic correction is desired, a previously determined correction factor are applied to the amplitude values. In this way, the impedance cardiographical signal can be corrected as a function of the detected pulse wave velocity. Likewise, further examinations can be initiated when the second warning signal occurs.

According to the invention, a known impedance cardiography device can be substantially improved by the described application of either a humeral cuff or a thigh pressure cuff. In this case, the described different error sources of a conventional measurement of the heartbeat volume are detected and signaled. Particularly preferred ^¬ embodiments are the both the Oberarmdruckman- cuff and the thigh pressure cuff in addition to

Use impedance cardiography device.

With the help of additional information it is

possible to evaluate the vascular system and simultaneously make an assessment of the extent to which may be restricted ^¬ vascular elasticity can affect the accuracy of the determination of the stroke volume using impedance cardiography. This restriction can be displayed to the user and corrected if necessary. The arrangement according to the invention thus allows the automatic signaling of missing reliability or accuracy of the impedance cardiac-determined heartbeat volume. In addition, information is provided that can be used in a subsequent diagnosis. LIST OF REFERENCE NUMBERS

01 current electrode

02 current electrode

03 measuring electrode

04 measuring electrode

05 evaluation and control unit

06 upper arm drumming

07 first transducer

08 Overhead pressure gauge

09 second transducer

Claims

claims

1. Arrangement for noninvasive detection of haemodynamic

Parameter comprising:

- means for recording an impedance cardiographical

Signal having at least two current electrodes (Ol, 02) and at least two measuring electrodes (03, 04) for attachment to the thorax of a patient;

- An evaluation and control unit (05), the left ventricular from the impedance Kardiographischen signal

Expulsion time LVET _IKG and / or the date of

Aortic valve opening (B point) extracted;

characterized in that the arrangement further comprises a humeral cuff (06) and / or a thigh pressure cuff (08), each on the upper arm or

Thighs of the patient are attachable and detect when Beauf ^¬ regurgitation with a predetermined pressure there a pulsative pressure change, which are fed via transducer (07, 09) as Oberarm- or thigh pressure signal of the evaluation and control unit (05), and that the evaluation and control unit (05) depending on the available pressure signal:

- from the upper arm pressure signal from a left ventricular ^¬ treibungszeit LVETp determined and this with the left ventricular ejection time LVET _ICG compares;

and or

- determines an aortic pulse wave velocity from the time difference between the B point in the impedance cardiograph signal and the occurrence of the associated pressure change in the femoral pressure signal; and

- Warning signals generated when the difference between LVET _P and LVET _IKG and / or the pulse wave velocity are outside ^¬ predetermined tolerance ranges. Arrangement according to claim 1, characterized in that it comprises both the upper arm pressure cuff (06) and the upper ^¬ thigh pressure cuff (08), and that evaluated both the upper arm pressure signal and the thigh pressure signal from the evaluation and control unit (05) for generating the warning signals become.

Arrangement according to claim 1 or 2, characterized in that the evaluation and control unit (05) which from the impedance-danzkardiographischen signal extracted left-ventricular ejection time LVET _IKG by the extracted from the left ventricular ejection time Oberarmdrucksig ^¬ nal LVET _P replaced when the difference between LVET _P and LVET _{IKG is} outside the specified tolerance range.

Method for non-invasive detection of haemodynamic parameters comprising the following steps:

- recording an impedance cardiographic signal of the change in blood volume in the thorax;

- Extraction of left ventricular ejection time LVET _IKG and / or the time of aortic valve opening

(B-point) from the impedance cardiographical signal;

- detecting a pulsatile pressure change at the brachial artery of the patient and generating an upper arm pressure signal and / or detecting a pulsatile pressure change at the femoral artery of the patient as well as genes ^¬ centering a femoral pressure signal;

- Extract a left ventricular expulsion time

LVETp from the upper arm pressure signal, unless this has been generated, and comparison with the data extracted from the left ventricular ejection time signal impedanzkardiogra ^¬ phical LVET _IKG, and / or detecting the temporal Diffe ^¬ rence between the B point in impedanzkardiographischen Signal and the occurrence of the associated pressure change in the thigh pressure signal, if it has been generated, and calculating the aortic pulse wave velocity; and generating warning signals when the difference between LVETp and LVE _IKG and / or the pulse wave velocity are outside predetermined tolerance ranges.

A method according to claim 4, characterized in that the recording of the impedance cardiographical signal by means of an impedance cardiograph device, to which at least two current electrodes (Ol, 02) and at least two measuring electrodes (03, 04) are connected, which are attached to the thorax of the patient.

A method according to claim 4 or 5, characterized in that the pressure change at the brachial artery is detected by means of a humeral cuff (06), which is attached to the upper arm of the patient and subjected to a predetermined pressure.

Method according to one of claims 4 to 6, characterized in that the pressure change is detected at the femoral artery using a thigh pressure cuff (08) which is attached to the thigh of the patient and subjected to a predetermined pressure.

Method according to one of claims 4 to 7, characterized in that the pressure change of both the Brachial Arte ^¬ theory and the femoral artery detected and evaluated to genie ^¬ tion of the warning signals. Method according to one of claims 4 to 8, characterized in that the is obtained from the impedanzkardiographischen signal extracted left-ventricular ejection time LVET _IKG by the extracted from the upper arm pressure signal linksventriku ^¬-cellular ejection time LVET _P replaced when the Diffe ^¬ ence between LVET _P and LVET _IKG outside the predetermined tolerance range is.

A method according to any one of claims 4 to 9, characterized in that the amplitude value of impedanzkardiographi ^¬ rule signal is subjected to a correction factor if the calculated aortic pulse wave velocity is outside the predetermined tolerance range.