DE102010016172A1 - Arrangement and method for non-invasive detection of haemodynamic parameters - Google Patents

Abstract

The invention relates to an arrangement for the non-invasive detection of hemodynamic parameters which are required in particular to determine the heartbeat volume. The arrangement comprises at least two current electrodes (01, 02) and at least two measuring electrodes (03, 04) for attachment to the thorax of a patient, as well as an evaluation and control unit (05) which contains means for implementing an impedance cardiography device for recording an impedance cardiographic signal , from which the left ventricular expulsion time LVETIKG and the time of the aortic valve opening (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 pulsative change in pressure, which are fed to the evaluation and control unit (05). The evaluation and control unit (05) determines a left ventricular expulsion time LVETP from the upper arm pressure signal and compares this with the left ventricular expulsion time LVETIKG, or it determines an aortic pulse wave speed and it generates warning signals if the difference between LVETP and LVETIKG and / or the pulse wave speed is outside the range specified tolerance ranges. The invention also relates to a method for the non-invasive detection of hemodynamic parameters.

Description

The invention relates to an arrangement and a method for continuous, non-invasive detection of haemodynamic parameters, as they are needed in particular for determining the heartbeat volume.

Impedance cardiography (ICG) is a well-known method for the noninvasive and continuous determination of heartbeat volume and other hemodynamic parameters ( Kubicek WG, development and evaluation of an impedance cardiography system to measure cardiac output and other parameters - 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 _IKG , ie the time between the opening (B-point) and the closure (X-point) of the aortic valve, and the amplitude of the aortic valve impedance cardiographic signal 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 Anesthesia. Scand. 1976, 20, 313-320 ).

In addition, devices are known (Tensiomed arteriograph), 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 blockage 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.

A disadvantage of existing devices for performing impedance cardiography is that the X-point in the impedance cardiographic signal needed to determine left ventricular ejection time LVET _IKG and correlated with aortic valve closure is often not, for example, reflected pulse waves and / or other changes in venous system volume is clearly pronounced and consequently can not or can not be determined correctly. This may lead to significant deviations in the determination of left ventricular ejection time LVET _IKG and, consequently, to relevant errors in the calculation of 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 z. B. due to the fact that, inter alia, by arteriosclerotic changes and the associated stiffening of the vessels, the elasticity of the aorta may be limited. This results in the same heartbeat volumes to a smaller volume change in the thorax and consequently also to a lower impedance change, so that the amplitude of the measured impedance cardiographic signal dZ / dt _{max is} reduced. As a result, the heartbeat volume determined by 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. This does not recognize that the measured amplitude of the impedance cardiograph signal dZ / dt _max does not correctly reproduce the heartbeat volume, which also leads to errors in the calculation of the heartbeat volume.

The US 2009/0259132 A1 describes a method and apparatus for determining heartbeat volume by bioimpedance measurement on a patient's upper arm using pulsation in the arteries. In this connection, it is proposed to determine the LVET from a pulse oximetry signal or its first derivative. Alternatively, the LVET may be determined from an applanation tonometry signal or its first derivative. In particular, the influence of the upper arm can reduce the influence of errors from diseased fluid deposits in the thorax. 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.

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 ejection time LVET and the influence of a possibly reduced vascular elasticity on the amplitude of the impedance cardiographic signal dZ / dt _max automatically detect and take into account in determining the heartbeat volume.

The object is achieved by an arrangement according to claim 1 and a method according to claim 4.

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.

In addition, in addition to the impedance cardiography device, the arrangement according to the invention comprises an upper arm pressure cuff and / or a thigh pressure cuff and one or more associated transducers which evaluate the upper arm pressure pulse curve and / or the thigh pressure pulse curve.

The pressure pulse curve derived from an upper arm of the patient with the help of the humeral cuff is converted into an electrical signal by the humeral force pulse curve transducer and used to determine left ventricular expulsion time LVET _P irrespective of the remaining cardiac impedance device.

The calculation of the heartbeat volume takes into account both the left ventricular expulsion time LVET _IKG obtained on the basis of impedance cardiography and the left ventricular expulsion time LVET _P obtained from the upper arm pressure pulse curve. If there are more permissible deviations between the independently obtained values of the expulsion time than within a predefined time tolerance range, a first warning signal is generated, which indicates that the measured values supplied by the ICG are not trustworthy. 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 given tolerance range, in a modified embodiment, a mean value of LVET _IKG and LVET _{P can be} 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 correlates with the degree of vascular stiffness.

Simultaneously or alternatively to the humeral cuff, therefore, the pressure pulse curve derived from a thigh of the patient with the help of the thigh pressure cuff is converted into an electrical signal by the thigh pressure pulse curve transducer and used to determine the central pulse wave velocity, which is subsequently also checked by IKG in the validation test measured values and, if necessary, in the calculation of the heartbeat volume is taken into account. If a pulse wave velocity lying outside of a predetermined speed tolerance range is detected, a second warning signal is generated which indicates that the measured values supplied by the IKG are untrustworthy. In this case, in particular, the amplitude values of the recorded impedance cardiographical signal are faulty, namely too small.

To correct the amplitude values, a correction factor can be applied as a function of the determined pulse wave velocity, which can be determined empirically, for example, by evaluating numerous measurement series. In the simplest case, the signaling of a pulse wave velocity lying outside the specified tolerance range can also be used by the user to initiate further examinations in the patient.

An essential advantage of the invention is that the inclusion of the upper arm pressure pulse curve provides an additional possibility for determining the left ventricular expulsion time LVET _P , and thus the left ventricular expelling time LVET _IKG determined on the basis of the impedance cardiogram can be verified and optionally automatically corrected, which leads to an increase in the accuracy of impedance cardiography.

A further advantage of the invention is that the aortic pulse wave velocity determined by inclusion of a femoral pressure cuff provides information about the elasticity of the aorta, on the basis of which it 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. Show it:

1 a schematic representation of the components of an inventive arrangement and the positioning of sensors on the patient;

2 a representation of waveforms that can be recorded with the inventive arrangement.

1 illustrates both the components of an inventive arrangement as well as the positioning of multiple sensors on the patient. To determine the stroke volume of the heart by means of. Impedance cardiography (ICG) is performed in a known manner at the thorax of the patient two or more current electrodes 01 . 02 applied, over which a very low, high-frequency and constant alternating current is fed, which flows through the body portion to be examined. Between the current electrodes 01 . 02 become two or more measuring electrodes 03 . 04 arranged, with the aid of which an electrical voltage can be measured, which varies depending on the volume of blood pumped into the body during a heartbeat. If, therefore, the blood volume in the examination section changes, so does its electrical impedance. 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 located and capture the body section to be examined.

The arrangement has an evaluation and control unit 05 , which initially includes all conventional means for performing an impedance cardiography. The evaluation and control unit 05 supplies the measuring current to the current electrodes 01 . 02 and receives the recorded measurement data from the measurement electrodes 03 . 04 , Since the possibilities for constructing a conventional IKG device are known to the person skilled in the art, a detailed description of the known components of the evaluation and control unit is dispensed with.

Using the impedance cardiography (IKG) measuring arrangement described, the in 2 The curve (a) represents the measured impedance change -dZ (referred to as IMP) and the curve (b) represents the first mathematical derivative of the curve (a) that is -dZ / dt, which is referred to as IKG. For a better understanding, the chronologically associated course of the signal recorded by an electrocardiogram is also shown as curve (c).

B

– Öffnen der Aortenklappe,

X

– Schließen der Aortenklappe und

C

– maximaler systolischer Fluss,

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 left ventricular expulsion time LVET _IKG .

As mentioned above, as a result of pathological changes in the vascular system of humans, the vascular elasticity may be greatly reduced. This has the consequence that the propagation speed of the pressure pulse curve in the aorta is greatly increased and the pressure pulse curve reflected by the periphery again reaches the aorta and the heart during the 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 collections in the thorax. As a result, the X-point may shift in the IKG curve so that it no longer reflects exactly the closure of the aortic valve. If the X-point in the IKG is determined incorrectly, this has a direct influence on the determination of the left ventricular expulsion time LVET _IKG and consequently leads to an erroneous calculation of the stroke volume of the heart.

In order to solve this methodological problem, according to the invention a humeral cuff is provided on the upper arm of the patient 06 placed, which is occupied with a predetermined pressure. This creates a coupling to the brachial artery and its pressure changes to the humeral cuff 06 transfer. The pressure changes detected by the humeral cuff are measured using a first transducer 07 converted into an electrical signal and to the evaluation and control unit 05 delivered. The signal delivered by the first transducer represents a humeral pressure pulse curve, unlike that of the measuring electrodes 03 . 04 delivered IKG signal - only to a small extent influenced by reflected pressure pulse curves and not by venous processes or fluid collections in the thorax. Thus, a second possibility for determining the aortic valve closure and consequently the left ventricular expulsion time LVET _{P is} given, which in the case of pathological changes in the vascular system in any case other, usually also more accurate values than the derived from the thorax LVET _IKG .

Through the evaluation and control unit 05 For example, the left ventricular expulsion time LVET _P determined from the upper arm pressure pulse curve is compared at regular intervals or for a given occasion with the left ventricular expulsion time LVET _IKG determined from the impedance cardiographical curve. If both values deviate from each other by more than a predetermined time tolerance, a first warning signal is generated, indicating that the metrics provided by the IKG are untrusted. By the first warning signal can then be preferably made that the determined from the pressure pulse curve left ventricular expulsion time LVET _{P is used} to determine the stroke volume of the heart. In this way, a left ventricular ejection time LVET _IKG erroneously determined in the impedance cardiograph signal can be recognized and corrected as desired, thereby increasing the reliability and accuracy of determining the heartbeat volume.

As a rule, the continuous determination of left ventricular ejection time continues to be based on the signal recorded by the ICG device integrated in the device according to the invention, so that long-term measurements can be carried out without significant impairment of the blood circulation in the patient's upper arm.

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 evaluated in impedance cardiography for determining the stroke volume of the heart. 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.

Decreased elasticity of the aorta may also result in a reduction of the aortic windrowing function, with the result that the corresponding volume of stroke in the heart is reduced in the aorta, resulting in a reduction of the C-spot (dZ / dt _max ) in the aorta impedance cardiographic signal and thus leads to an underestimation of the heartbeat volume on the basis of impedance cardiography. Under these conditions, however, the pulse wave velocity is increased. This means that the pulse wave velocity correlates with the elasticity of the vessels.

In order to determine the pulse wave velocity in the aorta, according to the invention, a thigh pressure cuff is placed on the thigh of the patient 08 placed, which is occupied with a predetermined pressure. This creates a coupling to the femoral artery and its pressure changes on the femoral pressure cuff 08 transfer. The of the thigh pressure cuff 08 recorded pressure changes are using a second transducer 09 converted into an electrical signal and to the evaluation and control unit 05 delivered.

The thus obtained femoral pressure pulse curve allows a clear determination of the time at which the pulse curve the thigh pressure cuff 08 has reached. At the same time the B-point, ie the time of the aortic valve opening, is determined in the impedance cardiographic signal. The time difference between the moment of the aortic valve opening (B point) and the time at which the pressure wave is the femoral pressure cuff 08 has reached defines the propagation time of the pulse wave. By relating this time to the distance between the aortic valve and the position of the femoral pressure cuff, one obtains the aortic pulse wave velocity, which in turn correlates with the elasticity of the aorta. If the determined pulse wave velocity lies outside a predefined speed tolerance range, then a second warning signal is generated, which indicates that the measured values supplied by the ICG are not trustworthy. In this case, in particular, the amplitude values of the impedance cardiographical signal are erroneous. If automatic correction is desired, a previously determined correction factor may be applied to the amplitude values. In this way, the impedance cardiographic signal can be corrected in dependence on 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 significantly 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 those which use both the humeral cuff and the femoral pressure cuff in addition to the impedance cardiograph apparatus.

With the help of the additionally obtained information, it is possible to evaluate the vascular system and at the same time make an estimate of the extent to which a possibly limited vascular elasticity can influence the accuracy of the determination of the heartbeat volume by means of impedance cardiography. This restriction can be displayed to the user and corrected if necessary. The arrangement according to the invention thus permits the automatic signaling of missing reliability or accuracy of the cardiac stroke volume determined by impedance cardiography. Furthermore Information is supplied 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 pressure cuff

07

first transducer

08

Thigh pressure cuff

09

second transducer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2009/0259132 A1 [0008]

Cited non-patent literature

• Kubicek WG, development and evaluation of an impedance cardiography system to measure cardiac output and other parameters - NASA CR 101965, 1969 [0002]
• Left Ventricular Ejection and the Heather Index Measured by Non-Invasive Methods during Postural Changes in Man: DW Hill, AJ Merrifield, Acta Anesthesia. Scand. 1976, 20, 313-320 [0003]

Claims (10)

Arrangement for the noninvasive detection of hemodynamic parameters, which are needed in particular for determining the heartbeat volume, comprising - at least two current electrodes ( 01 . 02 ) and at least two measuring electrodes ( 03 . 04 ) for attachment to the thorax of a patient; - an evaluation and control unit ( 05 ), which contains means for realizing an impedance cardiography device and to which the current and measuring electrodes ( 01 - 04 ) are connected in a manner known per se, for recording an impedance cardiographic signal, from which the left ventricular expulsion time LVET _IKG and the time of the aortic valve opening (B point) are extractable; characterized in that the assembly further comprises an upper arm pressure cuff ( 06 ) and / or a thigh pressure cuff ( 08 ), which are each attachable to the upper arm or thigh of the patient and when acted upon with a predetermined pressure there detect a pulsative pressure change, which via measuring 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 a left ventricular expulsion time LVET _{P is} determined and compared with the left ventricular expulsion time LVET _IKG ; - 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 - generates warning signals 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 both the upper arm pressure cuff ( 06 ) as well as the thigh pressure cuff ( 08 ), and that both the upper arm pressure signal and the thigh pressure signal from the evaluation and control unit ( 05 ) are evaluated to generate the warning signals. Arrangement according to claim 1 or 2, characterized in that the evaluation and control unit ( 05 ) replaces the left ventricular expulsion time LVET _IKG extracted from the impedance cardiac signal with the left ventricular expulsion time LVET _P extracted from the upper arm pressure signal when the difference between LVET _P and LVET _{IKG is} outside the predetermined tolerance range. Method for the non-invasive detection of hemodynamic parameters, which are needed in particular for determining the heartbeat volume, comprising the following steps: - recording an impedance cardiographical signal of the change in blood volume in the thorax; - Extraction of left ventricular ejection time LVET _IKG and the time of aortic valve opening (B point) from the impedance cardiographic signal; Detecting a pulsatile pressure change at the brachial artery and / or at the femoral artery of the patient and generating a humeral or thigh pressure signal; Extracting a left ventricular ejection time LVET _P from the upper arm pressure signal and comparing it with the left ventricular ejection time LVET _IKG extracted from the impedance cardiographical signal; - detecting 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 calculating the aortic pulse wave velocity; and generating warning signals when the difference between LVET _P and LVET _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 is carried out with means for realizing an impedance cardiography device comprising at least two current electrodes ( 01 . 02 ) and at least two measuring electrodes ( 03 . 04 ), 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 by means of a humeral cuff ( 06 ), which is attached to the upper arm of the patient and applied with a predetermined pressure. Method according to one of claims 4 to 6, characterized in that the pressure change at the femoral artery by means of a thigh pressure cuff ( 08 ), which is attached to the thigh of the patient and applied with a predetermined pressure. Method according to one of claims 4 to 7, characterized in that the pressure change of both the brachial artery and the femoral artery detected and evaluated to generate the warning signals. Method according to one of claims 4 to 8, characterized in that the extracted from the impedance cardiographical signal Left ventricular expulsion time LVET _{IKG is} replaced by the left ventricular expulsion time LVET _P extracted from the upper arm pressure signal when the difference between LVET _P and LVET _{IKG is} outside the predetermined tolerance range. Method according to one of claims 4 to 9, characterized in that the amplitude value of the impedance cardiographical signal is applied with a correction factor when the calculated aortic pulse wave velocity is outside the predetermined tolerance range.

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