DE10061189A1 - Method for continuous determination of mean, systolic and diastolic arterial blood pressure by measurement of the pulse transition time using electrodes measuring impedance of separate body regions - Google Patents

Method for continuous determination of mean, systolic and diastolic arterial blood pressure by measurement of the pulse transition time using electrodes measuring impedance of separate body regions

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Publication number
DE10061189A1
DE10061189A1 DE2000161189 DE10061189A DE10061189A1 DE 10061189 A1 DE10061189 A1 DE 10061189A1 DE 2000161189 DE2000161189 DE 2000161189 DE 10061189 A DE10061189 A DE 10061189A DE 10061189 A1 DE10061189 A1 DE 10061189A1
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Prior art keywords
blood pressure
characterized
map
method according
determined
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Withdrawn
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DE2000161189
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German (de)
Inventor
Ingo Stoermer
Peter Buttgereit
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Ingo Stoermer
Peter Buttgereit
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Priority to DE2000161189 priority Critical patent/DE10061189A1/en
Publication of DE10061189A1 publication Critical patent/DE10061189A1/en
Application status is Withdrawn legal-status Critical

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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/02108Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
    • A61B5/02125Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave propagation time
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026Measuring blood flow
    • A61B5/0285Measuring or recording phase velocity of blood waves
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/05Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radiowaves
    • A61B5/053Measuring electrical impedance or conductance of a portion of the body
    • A61B5/0535Measuring electrical impedance or conductance of a portion of the body impedance plethysmography

Abstract

Method for continuous determination of the arterial blood pressure uses the pulse transition time (PTT) in which the time of pulse arrival at two different body points is measured and then the difference between the two determined, from which a value for blood pressure is determined. Accordingly each sensor has two electrodes (1-6) that measure the impedance of the body region and the mean arterial blood pressure from the corresponding PTT. The invention also relates to a corresponding device.

Description

The invention relates to a method for continuous, non-invasive determination of arterial blood pressure Measurement of the pulse wave transit time (PTT: Pulse Transition Time), at that on at least two areas of a patient's body gnale be taken from the time difference between correct sponding points of the two signals the pulse wave transit time determined and a value for blood pressure is derived from it.

Such a method is, for example, from WO 00/10453 known. In the known method, the heartbeat caused pulse wave at two distant locations of the Body of a patient recorded, this being pressure sensitive Sensors are used to detect the rash on the skin surface che caused by the heartbeat and the resulting pressure wave is generated. The two away from each other at the Skin of the patient's recorded signal becomes one Derived time and then the pulse wave transit time by determining the time shift between charak teristic points of the measurement signal curves determined. From the  Pulse wave runtime can be after a calibration constant te is a measure of mean arterial blood pressure derived.

Such a method for continuous measurement and monitoring Monitoring a patient's blood pressure is unreliable and can have considerable inaccuracies, since they are already minor Movements of the patient falsify the measurement signals from the sensors can.

Other methods of determining blood pressure based on the Pulse wave transit times use photoplethysmographs as sensors or ultrasound Doppler. With the latter you can practice Achieve suitable results, the effort involved in placement however, the transducers and the cost of use are too high to to be suitable for everyday clinical use. Photoplethysmogra phen are comparatively inexpensive, but they are based on that Registration of volume pulses of the peri pheric arteries (muscular type arteries). The Volume pulse of the arteries of the muscular type is due to the seen from the heart, severe narrowing of the vessels around the Factor 2,500 due to reflections and overlaps tugging so the calculation of the pulse wave speed too becomes inaccurate. Another disadvantage of determining the pulse wave Oil run time using photoplethysmographs is that the Blood flow to the terminal current path in critical circulatory systems tuations (e.g. centralization in case of shock) or in Cold (cold hands) is very limited, so in in such situations no signal can be registered anymore, what is particularly unsatisfactory, especially in critical situations precise blood pressure values are required.

In the article "Clinical evaluation of continuous non-invasive blood pressure monitoring: Accuracy and tracking capabilities ", Christopher C. Young et al., Journal of Clinical Monitoring, Vol. 11, No. 4, July 1995, pages 245-252, the accuracy was the blood pressure measurement over the pulse wave duration, which means  two photometric cells located on the body was determined with the results recorded simultaneously compared to an invasive blood pressure measurement. The invasive blood pressure measurement with one on a catheter in an artery introduced sensor works, is currently the most precise Available method as it is a direct measurement of the parameters of interest. The precision of the direk However, measurement is due to problems due to natural frequency and system damping is the subject of controversial discussion. Nevertheless, the comparison in the article mentioned shows that over the pulse wave transit time, determined by photome trical pulse sensors, blood pressure values were often not good matches the more precise, invasively measured blood pressure values agree and moreover in a relatively long period of time are not available. Furthermore, the pulse wave running is not time in central arteries (elastic type arteries) summarizes the parameters to be determined (central blood pressure) reflects.

It is an object of the present invention to provide a method for continuous determination of arterial blood pressure by To improve the measurement of the pulse wave transit time so that the ver drive reliably and precisely and with little effort is applicable.

The characteristic features serve to solve this task of claim 1 in conjunction with its preamble. Advantageous embodiments of the invention are in the sub claims listed.

According to the present invention, in at least two bodies areas, preferably on the thorax and lower leg, a Measurement signal representing impedance recorded. The impedance can z. B. simply with four Elek glued to the skin trodes operated by a control and evaluation unit will determine. It is known that changes in impedance change fluid content in the examined body area  reflect, so the time course of the impedance is suitable by comparing at least two the impe danz representative measurement signals that are separated from each other ten positions are added to the pulse wave transit time voices.

The time derivative of the recorded measurement signal is preferred le are formed, and local extreme values, e.g. B. Maxima in the time derivatives that determines the points of maximum slope correspond to the impedance, and from the time shift these maxima against each other a value for the pulse wave transit time certainly. Furthermore, the recorded measurement signals or their Time derivatives are used to increase the cardiac cycle duration determine.

Are two sensors z. B. in the thorax and Be attached to the lower leg and from characteristic Points of the impedance curves determines the pulse wave transit time, see above you get the pulse wave transit time of the central current path. The Distortion of the pressure and current curves is in this area comparatively low, so the precision of the process at least in the area of the most precise procedures so far, namely invasive measurement using a catheter.

The pulse wave propagation time can be used to find a suitable calibra immediately determine the mean arterial blood pressure.

Furthermore, with the method of the present invention also the values of systolic and diastolic blood pressure can be determined, with the relationships used Darge in the following detailed description of the invention be put.

The inventive method is particularly advantageous because with the impedance is a simple and reliably measurable parameter is used, which is simply with two by default and electrodes available at low cost  can be. The patient's impairment is different with invasive methods or measurement using a permanent adjacent pressure cuff, minimal. In addition, the Measurement robust and less prone to failure and also delivers in critical conditions situations with a concomitant lack of blood flow to the terminal current path reliable blood pressure values.

The invention is described below using exemplary embodiments described in the drawings in which:

Fig. 1 is a schematic illustration of the pressure course during a cardiac cycle;

Figure 2 is a schematic representation of an apparatus for performing the method;

Fig. 3 is a schematic representation of the recorded measurement signals;

FIG. 4 shows representations of the pressure variation during a cardiac cycle in different areas with increasing distance from the heart are;

Fig. 5 is a graph in which the measured with the present invention, blood pressure values are compared with invasively measured values.

According to Fig. 2 and 3 is preferably in the present process with two electrodes 1 and 2 which are at a distance from each other in a first body portion, preferably as shown in the thorax mounted, and two electrodes 3 and 4, which was on from one another on the Lower leg are attached, the AC resistance Z (or a measurement signal representing the impedance) between the electrodes of the two electrode pairs 1 , 2 and 3 , 4 is recorded as a measurement curve. For this purpose, a weak, high-frequency alternating voltage is applied to the head and foot of the patient via the further electrodes 5 , 6 , so that a voltage can be recorded in each case between the electrode pairs 1 , 2 and 3 , 4 .

In the device shown in FIG. 2, the time derivative dZ / dt of the recorded measurement signals is first formed and the time derivatives are then subjected to various filtering, namely in a 50 Hz bandstop filter 12 , a 5 Hz high pass filter 14 and a 16 Hz low pass filter 16 , after which the signals are subjected to an A / D conversion in an analog / digital converter device 18 . In the control and evaluation unit 20 , which is preferably formed by a suitably programmed computer, the recorded measurement signals are fed to various examinations and processes.

In the control and evaluation unit 20 , the successive evaluation steps are shown schematically as in a flow chart. In step 22 , the time derivatives of the recorded impedance functions are searched for local extreme values. In step 24 there is a further pattern recognition in order to reliably identify characteristic points in the curve profiles. By determining maxima in the time derivatives, z. B. find the points of maximum increase in the impedance function.

To determine the pulse wave transit time PTT, a characteristic point is determined within each cardiac cycle from the measurement signals representing the impedance in the selected body segments (preferably thorax and lower leg) (e.g. local maximum in the derivation of the measurement signal according to the time, what the point corresponds to the maximum slope in the impedance signal). By. Determination of the time shift between the characteristic points, as illustrated in FIG. 3, determines the pulse wave transit time PTT.

The calculation of mean, diastolic and systolic blood pressure, the procedures being described below, takes place in step 30 . Calibration constants designated 32 are included. The results are finally displayed on a display screen 40 .

In the illustrated embodiment, due to the additional electrodes 5 on the head and 6 on the patient's foot, high-frequency weak alternating voltage can be tapped via the electrode pairs 1 , 2 and 3 , 4 voltages and thereby the impedances between the electrodes 1 , 2 and 3 , 4 lying body segments representing measurement signals are derived.

Furthermore, it is possible in this embodiment to record an EKG curve via the electrodes 1 , 2 on the thorax. The additional recording of an EKG curve enables further parameters, such as the pre-ejection period (PEP) and the cardiac cycle duration, to be determined by comparing the ECG curve with the time derivatives of the impedance curves. An estimate for the pulse wave transit time can also be obtained by means of the ECG curve and a measurement signal curve if the other measurement signal cannot be evaluated due to a disturbance.

The determination of the mean arterial blood pressure MAP from the pulse wave transit time PTT can be carried out in the following manner. It is known that the modulus of elasticity and the pressure change are in a fixed relationship to one another, which is described by the following equations:

Here is:
C: pulse wave velocity
r: lumen radius
E: modulus of elasticity
h: wall thickness
V: arterial volume
P: pressure
ρ: blood density
PTT: pulse wave transit time
d: distance

The formulas can be assumed on the assumption that h, V, r, ρ can be regarded as approximately constant during a short observation period of a few hours

ΔP = const.c 2

simplify. The pulse wave velocity is of course inversely proportional to the pulse wave transit time, so that:

applies.

This relationship between mean arterial blood pressure MAP and the pulse wave time PTT was developed by Bramwell in 1922 described and later experimentally tested by Wetterer.

The mean arterial blood pressure is determined by means of oscillometric pressure measurement p 0 by the calibration factor k:

k = p 0 .PTT 2 .

In the following it is shown how the procedure can also be used diastolic and systolic blood pressure can be determined.

Fig. 4 shows the pressure profiles along the main arterial tube in a younger adult. One calls the pressure minimum at the end of the cardiac cycle as diastolic pressure, the pressure maximum in the course of the blood ejection phase of the heart as systemic pressure.

The elasticity and cross-section of the arteries decrease with increasing distance from the heart. This increases the pressure wave resistance, which leads to the systolic pressure increase, which can also be seen in FIG. 4. The extent of the pressure increase differs individually and changes e.g. B. with the age of humans.

The mean arterial blood pressure MAP is at a known pressure run as an integral over the pressure curve over the period of a cardiac cycle. If you win the pressure curve from an artery of an extremity (common is the radial artery or A. femoralis), results from the systolic pressure increase too high for the systolic pressure and for the mean and diastolic arterial pressure too low estimated value.

On the other hand, if the mean arterial blood pressure MAP is known, as in the present method from the determination of the pulse wave transit time PTT, then a fixed relationship to the MAP can be assumed for the determination of the central (near-heart) systolic and diastolic pressure: the near-heart pressure curve can be by a linear increase in pressure from diastolic to systolic followed by a linear decrease back to the diastolic value within the cardiac cycle. This approximate course is shown schematically in FIG. 1. The integral then results approximately as

With:
p = arterial pressure curve
Δp = pressure amplitude
p sys = systolic blood pressure
p dia = diastolic blood pressure
EP = volume ejection time of the heart
RR = cardiac cycle duration.

If, instead of the pressure profile close to the heart considered here, as shown in FIG. 1, a pressure profile remote from the heart is taken as a basis, instead of the arithmetic mean in the above relationship, a weighted average results which can be determined by calibration.

To determine the blood pressure amplitude, it is approximately assumed that the modulus of elasticity of the arterial vascular system is constant in the section under consideration:

Δp ∝ ΔV

with ΔV = volume change in the system.

Starting from the diastolic pressure p dia , there is a systolic volume change ΔV sys with each heartbeat, which is given by the heartbeat volume SV within the volume ejection time EP of the heart minus the outflowing volume k 2 .EP.MAP, which increases the arterial blood pressure by Δp sys increases to the systolic value p sys :

ΔV sys = SV - k 2 .EP.MAP

Δp sys ∝ SV - k 2 .EP.MAP

p sys = p dia + k 1. (SV - k 2 .EP.MAP)

where k 1 , k 2 are calibration constants.

There is also a volume outflow ΔV dia , since the blood, driven by the MAP, flows continuously from the arterial into the venous system against the flow resistance TPR (Total Peripheral Resistance). The TPR can be assumed to be constant within a heart cycle. The period considered below comprises a cardiac cycle duration RR. Starting from the systolic blood pressure, the volume loss leads to a pressure drop by ΔP dia proportional to the reduction in volume:

ΔV dia ∝ MAP. (RR - EP)

Δp dia ∝ MAP. (RR - EP)

p dia = p sys - k 2 .MAP. (RR - EP)

The blood pressure amplitude is always on the diastolic Previous cardiac cycle pressure superimposed.

Δp dia and Δp sys are equivalent expressions for blood pressure amplitude. The constants k1 and k2 in the above formulas are obtained by oscillometric calibration. From the above description it follows that the blood pressure amplitude ΔP dia and ΔP sys calculated with two alternatives need only be appropriately centered around the mean value MAP determined by PTT in order to obtain the systolic and the diastolic pressure, the following two calculation possibilities being given :

p sys = p dia + k 1. (SV - k 2 .EP.MAP) = MAP + k 1. (SV - k 2 .EP.MAP) .γ 1

p dia = p sys - k 1. (SV - k 2 .EP.MAP) = MAP - k 1. (SV - k 2 .EP.MAP). (γ 1 - 1) (1)

p dia = p sys - k 2 .MAP. (RR - EP) = MAP - γ 2 .k 2 .MAP. (RR - EP) = MAP. (1 - k 22. (RR - EP)) )

p sys = MAP. (1 + k 2. (RR - EP). (1 - 2γ 2 ))

where γ 1 , γ 2 are weighting factors.

If one assumes a pressure curve that deviates from that shown in FIG. 1, the weighting factors are included in the calibration.

Both of the above-mentioned alternatives ( 1 ) and ( 2 ) for determining p dia and are equivalent and can be used alternatively.

FIG. 5 shows the blood pressure values recorded over a longer period of time, which were determined according to the present method, in comparison with invasive, with a blood pressure values determined in the artery by an ordered pressure sensor. The data in both series of measurements were smoothed by moving averaging. The data were collected during anesthesia induction, which is responsible for the severe drop in blood pressure. The periodic influence of breathing on blood pressure can also be seen, even in the method according to the invention, which proves the accuracy and the good resolving power of the method according to the invention.

The comparison in FIG. 5 shows that the present method provides results which agree very well with those measured invasively. The present invention therefore allows the blood pressure monitoring to be carried out with much less effort and less uncomfortable for the patient than the invasive methods, the measurement accuracy and reliability of which is comparable to that of invasive methods.

Claims (18)

1. A method for the continuous determination of arterial blood pressure by measuring the pulse wave transit time (PTT), in which measurement signals are taken from at least two parts of a patient's body, the pulse wave duration determined from the time difference between corresponding points of the two signals and from this a value for the blood pressure is derived, characterized in that each sensor with at least two electrodes ( 1 , 2 ; 3 , 4 ) picks up a measurement signal representing the impedance in the body area, pulse duration is determined from the measurement signals in the two body areas and the mean arterial blood pressure is determined therefrom ,
2. The method according to claim 1, characterized in that a the measurement signal representing the impedance in the range of Thorax and another further peripheral (distant from the heart), approximately in the Area of the lower leg.
3. The method according to any one of the preceding claims, characterized characterized that the time derivative of the recorded Measurement signals formed and local extreme values in the time lines are determined to shift from the maxi ma or minima a value for the pulse wave transit time determine.
4. The method according to any one of the preceding claims, characterized characterized that the recorded measurement signals to do so used to determine cardiac cycle duration (RR).
5. The method according to any one of the preceding claims, characterized in that two further electrodes ( 5 , 6 ) are applied, with which an AC voltage is applied across the two body areas, and that with the two electrodes ( 1 , 2 ; 3 , 4 ) each sensor tapped the resulting voltages and determined the values representing the impedances in the body areas.
6. The method according to claim 5, characterized in that the further electrodes ( 5 , 6 ) are acted upon with different AC frequencies and an average value for the impedances is determined from the measurements at different frequencies.
7. The method according to claim 5 or 6, characterized in that the further electrodes ( 5 , 6 ) are attached to the head and foot of the patient.
8. The method according to claim 5, 6 or 7, characterized in that at least one EKG curve is recorded with the electrodes ( 1 , 2 , 3 , 4 ).
9. The method according to claim 8, characterized in that the ECG curve is used to increase the cardiac cycle duration RR determine.
10. The method according to claim 8 or 9, characterized in that the ECG curve and one of the measurement signals are used to estimate the pulse wave transit time hold if only one measuring signal due to a fault Available.
11. The method according to any one of the preceding claims, characterized in that the mean arterial blood pressure is determined by the relationship MAP = k / PTT 2 from the pulse wave transit time PTT, where k is an oscillometrically determined calibration constant.
12. The method according to any one of the preceding claims, characterized characterized that based on the from the measurement signals derived values for mean arterial blood pressure MAP and cardiac cycle RR values for the systolic  and diastolic blood pressure are derived.
13. The method according to claim 12, characterized in that the systolic blood pressure based on the relationship
p sys = p dia + k 1. (SV - k 2 .EP.MAP) = MAP + k 1. (SV - k 2 .EP.MAP) .γ 1
and the diastolic blood pressure based on the relationship
p dia = p sys - k 1. (SV - k 2 .EP.MAP) = MAP - k 1. (SV - k 2 .EP.MAP). (γ 1 - 1)
can be determined, where k 1 and k 2 are calibration constants and γ 1 are a weighting factor.
14. The method according to claim 12, characterized in that the diastolic blood pressure based on the relationship
p dia = p sys - k 2 .MAP. (RR - EP) = MAP - γ 2 .k 2 .MAP. (RR - EP) = MAP. (1 - k 22. (RR - EP)) )
and systolic blood pressure based on the relationship
p sys = MAP. (1 + k 2. (RR - EP). (1 - 2γ 2 ))
can be determined, where k 2 is a calibration constant and γ 2 is a weighting factor.
15. The method according to any one of the preceding claims, characterized characterized that the derived blood pressure values of a Subjected to smoothing filtering and displayed graphically.
16. The method according to claim 15, characterized in that the Smoothing filtering performed using a Kalman filter men will.  
17. Device for carrying out a method according to one of the previous claims.
18. The apparatus according to claim 17, with at least six electrodes ( 1 , 2 , 3 , 4 , 5 , 6 ) and a control and evaluation unit ( 20 ) which is prepared to represent a measuring signal representing the impedance between two electrodes ( 1 , 2 ; 3 , 4 ), to form the time derivatives of the two measurement signals, to recognize local extreme values in the time derivatives and to use them to determine the pulse wave duration and the heart cycle duration, from which, in turn, the mean arterial blood pressure, the systolic blood pressure, after calibration and the diastolic blood pressure can be derived and displayed.
DE2000161189 2000-12-08 2000-12-08 Method for continuous determination of mean, systolic and diastolic arterial blood pressure by measurement of the pulse transition time using electrodes measuring impedance of separate body regions Withdrawn DE10061189A1 (en)

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EP1388321A1 (en) * 2002-08-09 2004-02-11 Instrumentarium Oyj Method and system for continuous and non-invasive blood pressure measurement
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EP1424037A1 (en) * 2002-11-29 2004-06-02 Ela Medical Device for non-invasive measurement of arterial pressure, especially for the continuous ambulatory tracking of arterial pressure
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WO2009086921A1 (en) * 2008-01-11 2009-07-16 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Manometer, blood pressure manometer, method for determining pressure values, method for calibrating a manometer and computer program
US9119536B2 (en) 2008-01-11 2015-09-01 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Pressure gauge, blood pressure gauge, method of determining pressure values, method of calibrating a pressure gauge, and computer program
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