WO2009013287A1

WO2009013287A1 - Method for determination of a quasi-continuous blood pressure change in a pulsatile blood stream

Info

Publication number: WO2009013287A1
Application number: PCT/EP2008/059584
Authority: WO
Inventors: Thomas Hübner; Michael Alt
Original assignee: Enverdis Gmbh
Priority date: 2007-07-24
Filing date: 2008-07-22
Publication date: 2009-01-29
Also published as: EP2166933A1

Abstract

The invention relates to a method for quasi-continuous determination of the blood pressure in a blood stream, wherein a time profile of a volume pulse of the blood in a blood stream is first measured. Thereafter, the first derivation is formed over the time of the measured volume pulse profile. From this derivation of the volume pulse profile, the profile of a transverse speed of change of the cross section of the blood stream is determined. By calibration of the transverse speed of change of the cross section of the blood stream on the basis of conventionally determined blood pressure values, it is possible subsequently to derive a quasi-continuous profile of the blood pressure value from the volume pulse.

Description

A method for determining a quasi-continuous blood pressure change in a pulsatile bloodstream

The invention relates to a method for the non-invasive determination of a quasi-continuous change in blood pressure in a pulsatile bloodstream.

It is known that changes in blood pressure are accompanied by changes in pulse wave velocity. Pulse wave velocity is the rate at which a heart pulse propagates from the heart towards the akralen blood vessels. In order to be able to draw conclusions about the blood pressure, it has already been tried to determine the pulse wave velocity by various methods. The mathematical basics of the relationship between the pulse wave velocity and the blood pressure will be briefly explained below. It is based on the known formula according to Moens and Korteweg, which describes the pulse wave velocity in a cylindrical tube model as a function of the parameters of the vessel wall:

c = {h * E _t / (2 * p * R)} ^1/2

c Pulse velocity h Wall thickness of the blood vessel

R radius of the cylindrical blood vessel E _t tangential elastic modulus of the blood vessel p density of the fluid (blood)

The modulus of elasticity of the blood vessel is - as empirical studies show - dependent on blood pressure. In the range 60-180 mmHg, a linear dependence can be assumed as a first approximation:

E _t = E ₀ + E _p * p

E ₀ , E _p constants p blood pressure

With this assumption, the blood pressure p is calculated to:

p = {2PR / (E _p h)} * c ² - E _o / E _p

Thus, the blood pressure p increases with an increase in the pulse velocity in the pressure range of interest.

By a calibration measurement with a conventional sphygmomanometer, the constants {2pR / (E _p h)} and E "/ E _{p can be} initially determined. As a result, continuous blood pressure calculations based on the pulse wave velocity are possible.

A method used in practice for determining the pulse wave velocity relates to the determination of the pulse transit time, starting from the occurrence of the R wave in the ECG until the impact of the pulse wave on a sensor on an angled body part, eg an ear clip. This measured pulse transit time is used to calculate pulse velocity, from which in turn the blood pressure can be calculated. The relationship between blood pressure and pulse wave velocity is due to the fact that the vasomotor increase in the wall tension of the arteries on the one hand changes the blood pressure, but also the speed of Puisweile, ie the wave, which spreads from the heart in the Arterienwäπden. As the wall voltage increases, the pulse wave velocity is also increased.

The relationship between blood pressure and pulse wave velocity is actually more complex in practice. The pressure generated primarily by the work of the heart also plays a role. In addition, there is a regulating mechanism for adapting to different physical demands. If, for example, the blood pressure drops sharply, this is registered via sensors in the aortic arch and infoige of the wall tension is increased. Thus, the blood pressure rises and the previous pressure drop is compensated.

By the described method of blood pressure determination via the measurement of the pulse transit time, various vessel parameters, such as a constantly changing vessel diameter, structure and thickness of the vessels, anomalies, vessel branching and the extensibility of the vessel wall are not sufficiently considered. This limits the accuracy of this method.

An invasive continuous determination of the blood pressure is possible by means of catheter technology. However, this technique is laborious and involves high loads for the patient.

Non-invasive determination of blood pressure by inflated pressure cuffs is possible. Among other things is the

Voiumenkompensationsmethode known in which a finger cuff, in which a photoplethysmographic sensor and a pressure regulator are integrated, is used. By means of a transmission measurement of infrared light at the finger artery, the still penetrating infrared light component is determined. On the basis of the sensor signal, the pressure regulator is controlled in such a way that with reduced light flow (increased vessel diameter due to high pressure in the artery during systole), a back pressure is generated. With increased luminous flux (reduced vessel diameter due to decreasing pressure in the artery during diastole), the back pressure is reduced by the pressure regulator. On the basis of this permanent pulsation-related control of the back pressure, the vessel diameter remains unchanged. Therefore, the cuff pressure corresponds to the rantraarterial pressure, so that a determination of the blood pressure can be made.

Furthermore, it is known, in the context of the so-called AppSaπationstonornetrie defined to print the arteria radialis on a bone, so that based on this fixation of the blood vessel, the pulsation corresponding to the intra-arterial pressure can be measured by a pressure sensor directly through the skin.

It is also known to measure the change in the blood flow when closing the artery by means of a cuff, this point being dependent on the blood pressure, by using the ultrasound Doppler method. Ultrasonic waves of constant frequency are radiated obliquely to the longitudinal axis of the artery. These meet and are reflected by moving erythrocytes. The reflected waves have a different frequency than the originally irradiated waves due to the double effect. The change of the frequency is proportional to the flow velocity of the erythrocytes. Air is slowly released from the cuff and the altered frequency pattern is used to determine blood pressure at various cuff pressures.

Another known method is the oscillatory method. In this case, the pressure of an inflatable cuff, for example applied to the patient's upper arm, is determined, on which the blood pulse strikes. From the course of Registered pulse amplitudes when releasing the Maβschettendrucks can be closed to the blood pressure.

The object of the invention is to provide a method with which a quasi-continuous change in blood pressure in a bloodstream can be determined simply and reliably.

The object is achieved by the features of the claim

1,

In the method according to the invention for the quasi-continuous determination of the blood pressure in a bloodstream, the time course of a volume pulse of the blood in the bloodstream is measured. Subsequently, the first derivative is formed over the time of the measured Volumenpulsverlaufs. From this first derivative, the time course of a transversal rate of change of the cross section of the bloodstream is determined. Subsequently, a quasi-continuous blood pressure value is determined directly from this rate of change of the bloodstream cross section.

The relationship between the course of the transverse rate of change of the cross section of the bloodstream and the blood pressure to be determined is briefly described below.

The shape and amplitude of the pressure pulse, for example in the aorta, are influenced, inter alia, by the extensibility of the arterial vascular system. The aorta and large arteries act like a "wind cauldron" during the ventricular systole, attenuating the pressure fluctuations produced by the heart, and the pressure wave propagating from the heart along the vessels is increasingly attenuated due to the extensibility of the vessel walls in the more distant arteries The amount of amplification attenuation depends on the material properties of the blood vessels, the mean pressure in the vessels and the length and volume of the vessels. The strain-voltage curve for blood vessels is not a straight line (see DUCK, FRANCIS A. [1990], Physical Properties of Tissue, Academic Press), At higher pressures, the distensibility of the vessels decreases, ie that also the mentioned attenuation of the Pressure wave in the peripheral arteries is lower at high blood pressure levels. Due to the increase in blood pressure at lower blood pressure, and thus the lower attenuation of the pressure pulsations in the peripheral vessels also affects the rate of change of the blood vessel diameter. At a certain peripheral measuring point, the rate of change of the bi-path cross-section is thus a measure of the blood pressure.

The measured volume pulse course, which is also referred to as a plethysmogram, represents a change in volume and thus also the change in the cross section of the blood vessels. Particularly preferably, the calculation of the first derivative of the measured volume pulse course is not only for a single time, but over the entire time course. From this curve, the course of the transverse rate of change of the cross section of the Biutbahn can be determined at the site over time.

Based on the fact that the blood pressure causes the measured change rate of the bloodstream cross section, a continuous noninvasive determination of the blood pressure can thus take place.

Since the calculation of the blood pressure from the rate of change of the blood vessel diameter depends on a plurality of initially not exactly known physiological parameters, it is expedient to carry out a calibration of the rate of change of the bloodstream cross section by means of conventional blood pressure determination methods. The method according to the invention particularly preferably comprises carrying out a linearization step by measuring a reference blood pressure in a conventional manner, in particular, once, this reference blood pressure _ ^~~ _ j

are determined by a variety of known methods, wherein it is important that the method for determining the reference blood pressure, an absolute value is determined, which represents the correct blood pressure. The above-mentioned blood pressure measuring methods can be used for example for measuring the reference blood pressure.

Preferably, two Referenzmessuπgen be performed, wherein in each reference measurement in each case once the reference blood pressure and once the reference rate of change of the blood vessel diameter is measured. The first reference measurement can take place in a resting state, while in the second reference measurement by stress or by administration of appropriate medicaments a significant systolic blood pressure change, preferably of at least 20%, is generated. The stress can be generated, for example, by squats or other physical activities. The described reference measurements linearize the determined results for the quasi-continuous blood pressure curve. The nonlinear dependencies between the blood pressure and the rate of change of the blood vessel diameter that are present as a function of the respective physiological conditions can also be adapted by a higher order polygon.

It is particularly preferred that further parameters from the measured volume pulse course and / or the profile of the first derivative of the volume pulse course are used to determine the blood pressure. These may be, for example, maxima, minima or other prominent locations of the volume pulse profile. Furthermore, temporal differences between these prominent points of the volume pulse course and / or integrals between these points can be determined. The mentioned or further parameters can be investigated by means of linear or non-linear methods, in particular by determining the covariance and / or different correlation methods. The use of further suitable known mathematical methods is possible. As an additional or alternative Optimization methods can be used, for example, regression analyzes and / or neural networks.

It is particularly preferred that a continuous blood pressure curve is determined, which in particular comprises a systolic, a diastolic and a mean blood pressure value. A measured Volumenpuis course at a measuring point of the blood vessel is usually divided into a first phase (systole) and a second phase (diastole). In this case, for example, a value for the derivation of the Volumenpuisverlaufs can be determined at a prominent point of the Volumenpulsverlaufs during systole, which can be assigned according to a transverse rate of change of the cross section of the bloodstream. For example, a systolic blood pressure can now be determined from this rate of change of the bloodstream cross section for this particular time. In order to determine a diastolic blood pressure, it is accordingly possible to determine a value for the derivation of the Voiumenpulsverlaufs during the diastolic phase, which can be assigned to a corresponding value for the transverse rate of change of the cross-section of the bloodstream and a value for the Pulwellenπgeschwindigkeit at this time. Thus, also a diastolic blood pressure can be determined. Further possibly required blood pressure values at other times can be correspondingly determined by each determining a value for the derivation of the volume pulse profile together with the further required values for any other time.

Preferably, the measuring location for measuring the time profile of the volume pulse is formed as a small measuring point. This means that the measurement of the volume pulse profile does not take place over a certain distance, but only a very small measuring segment is considered. Preferably, the measurement of the time course of the volume pulse takes place at an akralen body part, for example, the earlobe of a patient, others suitable measuring points, such as the fingertip, can also be selected.

In a preferred embodiment of the invention, the volume pulse profile in the blood vessel is detected photoplethysmographically. For detecting the volume pulse course, first of all measuring radiation in the direction of a body part to be examined, for example a human finger or the earlobe, can be emitted. Subsequently, the radiation component of the measuring radiation reflected by the body part to be examined is detected. From the time course of the detected reflected radiation component of the measurement radiation, the time profile of the volume pulse at the measurement location is determined.

In addition to the detection of the reflected radiation component of the measurement radiation, the measurement radiation transmitted through the body part to be examined can be detected. The determination of the time profile of the volume pulse can then be based on the measured reflected and transmitted radiation component of the measurement radiation, which is described in particular by the Lambert-Beer law:

E = -log (1 / I ₀ ) = ε * c * d

E extinction

I exiting / transmitted intensity

I ₀ incident intensity ε molar extinction coefficient c concentration d layer thickness,

Lambert-Beer's law shows how the intensity of radiation passes through an absorbing material as a function of the radiation intensity Concentration of the substance behaves. The extinction is given as the logarithm of the ratio of the transmitted to the incident light

A suitable device for determining a Volumenpuisveriufs in a Biutbahn is described in the also filed by the Applicant German patent application "Apparatus for the continuous non-invasive determination of concentrations of various blood components". In contrast to the device described there, it is sufficient for the method according to the invention to determine the volume pulse course of a single blood constituent. Thus, the device described in said application need only comprise a radiation source for emitting a single wavelength. Other suitable devices may also be used to determine the volume pulse profile,

In the following, preferred embodiments of the invention will be explained with reference to figures.

Show it:

1 is a schematic representation of a device for determining a volume pulse course in a bloodstream,

Fig. 2 is a graphical representation of a measured

Voiumenpulsverlaufs with different prominent points,

3 is a graphical representation of the calculated first derivative of a measured volume pulse over time with various prominent points,

Fig. 4 is a graphical representation of a measured

Volume pulse course and its first derivative over time, 5 shows a graphic representation of the first derivation of a measured volume pulse profile with different prominent points, and FIG

Fig. 6a, 6b is a graphical representation of various

Baroreflexsensitivitätsverläufe. (Stefan H. Hohnloser;

Examination of baroreceptor function, Deutsches Ärzteblatt 96, Issue 25 (1999), p. 1716-1719),

Fig. 7 relationship between a from the first derivative of

Volumeπpulsverlaufs certain parameters and systolic blood pressure, and

Fig. 8 relationship between another from the first

Deriving the volume pulse course of certain parameters and the systolic blood pressure.

A device for the continuous determination of a volume pulse curve in a bloodstream has a radiation source 12 for emitting a measuring radiation 14 in the direction of a body part 16 to be examined (FIG. 1). More preferably, the body part 16 to be examined is a human finger. Alternatively, however, for example, the earlobe of a person, as well as other suitable body parts can be used for measurement.

Furthermore, the device 10 has a first radiation receiver 18 for receiving the radiation 20 reflected by the body part 16 to be examined. The first radiation receiver is arranged in the illustrated embodiment in the first receiving element 28. In this first Aufnahmeeiement 28 and the radiation source 12 is arranged. The device 10 further comprises a second radiation receiver 22 for receiving the radiation 24 transmitted through the body part 16 to be examined. The second radiation receiver 22 is arranged in the illustrated embodiment in the second receiving element 30, which is opposite to the first receiving element 28. Opposite in this context means that the two receiving elements 28, 30 and the first 18 and the second 22 radiation receiver are arranged such that, for example, a finger 16 can be positioned between them.

In Fig. 1, carried out by means of the device according to the invention reflection measurement is shown schematically. In this case, the radiation source 12 emits a measuring radiation 14. The emitted measuring radiation 14 is at least partially reflected by the body part 16 to be examined, so that a portion of the measuring radiation 14 is reflected as reflected radiation 20 in the direction of the first radiation receiver 18.

The measurement of the radiation 24 transmitted by the body part 16 to be examined is likewise shown schematically in FIG. In this case, the radiation source 12 emits a measuring radiation 14 in the direction of the body part 16 to be examined. At least a portion of the radiation 14 passes through the body part 16 to be examined and impinges on the second radiation receiver 22 as transmitted radiation 24. The first 18 and the second 22 radiation receiver are preferably designed as photodiodes. The device further comprises a calculation device 26, which is connected to the first 18 and the second 22 Strahiungsempfänger. The measured reflected 20 and transmitted 24 radiation components are fed to the calculation device 26 so that they can evaluate the determined curves on the basis of the measured radiation components. The radiation fraction transmitted through the body part in comparison to the emitted radiation can in principle be calculated by the Lambert-Beer law. However, by the inventive method for Blood pressure measurement preferably determines amplitudes at prominent points of the VolumeπpuJsveriaufs and its derivative, in particular maxima and minima, temporal differences between the prominent points and / or integrals between the prominent points. Standardization of the curves to a defined amplitude and possibly to a defined heart rate may also be expedient, so that the absolute intensity values to be calculated according to the Lambert-Beer law are dispensable.

The calculation device 26 can be designed, for example, as a PC on which a specific software program for carrying out the aforementioned calculations runs. In particular, these calculations can also be made on a PC at a different time than the measurement of the transmitted and reflected radiation. Thus, the calculation steps essential to the invention take place independently of the physical detection of the patient features described so far. The further described procedure steps can also be carried out without an interaction with the body of a patient, i. that their implementation does not require the presence of a patient's body.

The radiation source 12 is preferably formed as an LED and emits light of a wavelength that is particularly well absorbed by blood or its constituents. This may be, for example, the wavelength 805 nm +/- 10 nm.

By choosing a suitable wavelength, it is possible using the described device to determine a volume pulse course in a bloodstream, as shown in FIGS. 2 and 4 is shown. This volume pulse course is measured at a measurement point which is limited in its local extent, for example the earlobe or the human finger, and therefore describes the temporal change of the volume of the blood pulse at this measurement point Various salient points in the volume pulse curve that can be used for further calculations are also shown in FIG. In particular, these prominent points can also be included in the calculation of the blood pressure from the volume pulse course. Furthermore, differences on the time axis between different prominent points, for example the value "Diff 1" between the points "xl" and "x2" can be taken into account.

The course of the first derivative of the volume pulse profile shown in FIG. 2 is shown in FIG. This is the speed of the volume flow change. Again, several prominent points of the course of the derivative shown are marked. These can also be taken into account in the calculation of blood pressure »

The upper part of FIG. 4 also represents a measured volume pulse curve, while the lower part of FIG. 4 shows the profile of the first derivative of the volume pulse curve of the upper part of FIG. 4. The solid line represents the course of a low blood pressure, while the dashed line represents the course of a high blood pressure. Correspondingly, it can be seen from the lower part of FIG. 4 that the transverse rate of change of the cross section of the bloodstream at a high blood pressure is significantly higher at a low blood pressure.

Particularly prominent parameters that can be taken into account in the course of the first derivation over the time of the measured volume pulse course (transverse rate of change of the cross section of the bloodstream, as shown in the lower part of FIG. 4) are shown in FIG. These are in particular the following parameters:

Maximum amplitude of the first derivative in systole (Al) Time from the beginning of the period to the maximum of systole (tl)

Time from start of rise to next zero crossing in systole (t2)

Area under the curve from start of rise to the following zero crossing in systole (Fl)

Minimum amplitude of the first derivative in diastole (A2)

Time from the beginning of the period to the minimum of diastole (t3)

Time from the beginning of the rise to the following passage in the diastole (t4)

Below the curve from the beginning of the rise to the next Ninth time in diastole (F2)

It is particularly preferred that these parameters are also determined in the reference measurement or in the reference measurements as reference parameters. Based on the changes in these parameters from each heartbeat to the baseline value of the reference measurements, changes in blood pressure can be determined. Thus one obtains a quasicontinuous change in pressure from heartbeat to heartbeat in relation to the reference values. Since the described reference parameters can be detected both during systole and during diastole, it is possible to determine the change of these parameters at each time of systole and diastole, so that a corresponding blood pressure value can be determined for this time. In contrast, in a conventional blood pressure measurement, for example, with a cuff, the blood pressure can only be determined approximately every minute. As an application example of the invention, FIG. 7 shows the relationship between a parameter determined from the first derivation of the rate of change of the blood vessel diameter and the systolic blood pressure.

One possible parameter that correlates with blood pressure is the time difference between the maximum value and the following inflection point of the first derivative of the volume pulse curve. This quantity, referred to as "Parameter 1", corresponds to the time difference between the points "x2" and "xl2" in Figure 3 The correlation between "Parameter 1" and the systolic blood pressure determined by a reference procedure ("Finapress") is shown in Fig. 7. The respective points (stars) represent the frequency of these The percentages of the graph are plotted on the abscissa of the graph: the percentage deviation of the parameter l ^u from its original value (obtained at time 0):

The regression curve (straight line) shown in Fig. 7 can be described by the following equation:

p = P ₀ -C * X

p systolic blood pressure po constant (blood pressure at time 0, determined by reference method)

C constant (slope of the curve)

X Percent deviation of the parameter 1 ^ΛV from the value at time 0. (The "Parameter 1" is the time difference between the maximum value and the following inflection point of the first derivative of the volume pulse.) Preferably, the biometric pressure determined on the basis of the "parameter 1"("X") at 2 points (values of "parameter 1" at time O and 1: determination of X ₀ , Xi) is determined by a conventional method of blood pressure measurement (pressure values p ₀ , pi) The 2 points correspond to 2 different points in time at which the biological pressure, which may be influenced by the physical or mental stress of the patient or by medication, should differ as much as possible.This comparison can be made by the following mathematical relationships (Example after Fig.7) are described:

Time 0:

Po = 120 mmHg; systolic blood pressure X ₀ = 0 [%] Deviation of the parameter r ^Λ from time 0

Time 1:

P ₁ = po - C * Xi = 174 mmHg systolic blood pressure X ₁ = -20 [%] Deviation of "Parameter 1" from time 0

It follows:

In the example considered, the variation in "Parameter 1" by Xi = -20% changed the blood pressure from p ₀ = 120 mmHg to pi = 174 mmHg.

C = (120-174) / (- 20)

C = 2.7 The general context follows:

p [mmHg] = 120 - 2.7 * X

This allows the blood pressure to be determined with sufficient accuracy from the change in "Parameter 1" ("X", change in% compared with the value at time 0).

Another parameter that can be used to determine the blood pressure is parameter 2, namely the area of the first derivative of the pulse curve between its inflection point (time xl2 in FIG. 3) and the zero passage (time x4 in FIG. 3).

The approximately quadratic dependence between blood pressure and the "parameter 2" can be determined by an equation of the form

p = po - D (Z - Y) ^Z

to be discribed.

p systolic blood pressure

Po constant (blood pressure at time 0)

D constant

Y "Parameter 2": area of the 1st derivative of the pulse curve between its

Turning point according to fig. 3 as well as the nuIIMnIe (the percentage deviation of this parameter against the value at time 0 is used in the calculation)

Z constant

The curve according to Fig. 8 can be in the range of -25 <Y [%] <+80 by the formula p [mmHg] = 144 - 0.0041 * (80 - Y) ²

describe.

The calculation of the parameters p ₀ , D and Z can preferably be achieved by assigning the alternatively determined pressures pi, p ₂ and p ₃ to the associated values of the "parameter 2" (Y ₁ , Y ₂ and Y ₃ ) at 3 different times ( t _i; t ₂ and t ₃ ) At the various times, the "parameter 2" should differ as much as possible:

_Pl = po - D (Z - Y ₁ ) ² p ₂ = Po - D (Z - Y ₂ ) ² p ₃ = Po - D (Z - Y ₃ ) ²

This system of 3 independent equations allows the determination of the 3 unknown parameters p ₀ , D and Z.

Thus, the blood pressure from an arbitrary parameter Y - as far as the blood pressure values at the times ti, t ₂ and t _{3 represent} an "upward" (It. Fig. 8) convex curve - by the equation

p - po - D (Z - Y) ²

be determined.

Similarly, further relationships between appropriate parameters and associated blood pressure can be found empirically or through theoretical considerations. The invention further relates to a method for determining baroreflex sensitivity using the previously described noninvasive method for quasi-continuous blood pressure measurement, the aim of determining baroreflex sensitivity is to provide a measurement or analysis method which makes possible a risk stratification of patients, in particular after a heart attack, easy to do. In particular, it should be possible to perform this measurement routinely in clinical diagnostics.

The risk of patients after a heart attack can not be routinely determined individually in daily life in kinesin, so that the identification of the high-risk patients and thus the initiation of pattent-specific therapies is problematic. In determining the baroreflex sensitivity currently used in medical research, it is examined how the induced heart rate is related to the patient's blood pressure during induced exercise. From the baroreflex sensitivity parameters for the risk stratification of sudden cardiac death can be derived. However, the diagnostic and instrumentation effort required to measure baroreflex sensitivity is so high that this promising and often lifesaving diagnostic could not be established as a standard clinical trial. Rather, it has so far been located in the area of highly qualified clinics. The previously described method for non-invasive blood pressure determination makes it possible in a simple manner to determine a quasi-continuous blood pressure change required for determining the baroreflex sensitivity.

The method according to the invention for determining the baroreflex sensitivity can therefore comprise the method steps described so far for the non-invasive determination of a quasicontinuter surface change in blood pressure in a pulsatile bloodstream. Furthermore, as part of this method, a pulse detection takes place, so that the determined blood pressure values a respective Pulse value can be compared. This results in gradients, as shown in Fig. 6a and Fig. 6b.

Figure 6a shows as a dashed line (SAP) the course of the change in systolic blood pressure (beat to beat registration) over time, the solid line represents the change in the RR interval over time. Was measured under normal conditions and during a Drugs induced blood pressure increase. The drug is not administered for therapeutic purposes, but in the sense of a provocation test necessary for measuring purposes. Alternatively, a could

Increased blood pressure caused by a physical stress or physical impact on the patient, with such a provoked blood pressure increase is of course not for therapeutic purposes. For analysis, the values between the two vertical dashed lines are used. This results in a regression analysis of the blood pressure associated changes in the RR IntervaI! S of FIG. 6b. The increase in blood pressure is associated with a continuous prolongation of the RR interval. The slope of the regression line is about 20 ms / mmHg, which corresponds to normal baroreflex sensitivity.

In addition to the previously described detection of the rate of change of the blood vessel diameter, the heart rate is now detected, wherein the heart rate is preferably calculated from a simultaneously registered ECG. Preferably, a targeted influencing of the blood pressure, for example by medication, by physical effects on the patient (special storage, negative pressure generation on the legs or neck, temperature effect) or by mental impact. Alternatively, the detection of spontaneous blood pressure changes may be used to determine baroreflex sensitivity. The determined values can be evaluated statistically, for example by a determination of -? P -

Regression curves. Thus, the relationship between the detected rate of change of bloodstream cross-section (correlation with blood pressure) and heart rate can be used to assess baroreflex sensitivity.

Claims

claims

1. A method for the quasi-continuous determination of the blood pressure in a blood stream with the steps:

Measuring the time course of a Volumenpuis of the blood in a bloodstream,

Forming the first derivative over the time of the measured volume history,

Determine the course of a transversal rate of change of the cross section of the biofilm from the determined course of the first derivative over the time of the volume pulse course and

Determine a quasicontinuous course of blood pressure values from the transversal rate of change of the blood pressure

Bloodstream cross section,

2. The method according to claim 1, characterized in that the measurement of the time course of the Voiumenpulses exclusively takes place at a measuring point of the blood stream.

3. The method according to claim 1 or 2, characterized by the step: performing a linearization step by one or more times, preferably twice measuring a reference blood pressure (pi and p ₂ ) by a conventional method for blood pressure measurement.

4. The method according to any one of claims 1-3, characterized by the step: Performing a linearization step by in particular once measuring the rate of change of the bloodstream cross-section from the pulse curve.

5. The method according to any one of claims 2-4, characterized in that the outside of the determined allocation points between conventionally measured blood pressure and the associated rate of change of the bloodstream cross-section blood pressure values from the measured rate of change of Blutbahπquerschnitts be calculated by linear interpolation.

6. The method according to any one of claims 2-5, characterized in that for determining the blood pressure (p) further parameters from the measured volume pulse course and / or the course of the first derivative of the volume pulse curve are used.

7. The method according to claim 6, characterized in that belong to the parameters used amplitudes at prominent points of the Volumenpulsverlaufs and its derivative, in particular maxima and minima, temporal differences between the prominent points and / or integrals between the prominent points.

8. The method according to claim 6 or 7, characterized in that the further parameters are examined by means of linear or non-linear methods, in particular by means of a determination of the covariance and / or different correlation methods,

9. The method according to any one of claims 6 to 8, characterized in that the further parameters are examined by means of a regressions analysis and / or using neural networks,

10. The method according to any one of claims 1-9, characterized in that a continuous blood pressure curve is determined, which comprises in particular a systolic, a diastolic and a mean blood pressure value.

11. The method according to any one of claims 1-10, characterized in that the measurement of the time course of the VotumenpuSses on a Akrafen body part, in particular on the earlobe takes place.

12. The method according to any one of claims 1-11, characterized in that the Volumeπpulsverlauf is detected photoplethysmographisch.

13. The method according to claim 12, characterized in that the photochemical analysis of the volume pulse profile comprises the following steps:

Emitting a measuring radiation in the direction of a body part to be examined,

Detecting the radiation component of the measuring radiation transmitted through the body part to be examined,

Determining a time course of the volume pulse from the time profile of the detected transmitted radiation component of the measurement radiation.

14. The method according to claim 12, characterized in that the photoplethraphographic detection of the volume pulse profile comprises the following steps:

Emitting a measuring radiation in the direction of a body part to be examined, Detecting the radiation component of the measuring radiation reflected by the body part to be examined,

Determining a time course of the Volumeπpuises from the time course of the detected reflected radiation component of the measuring radiation,

15. The method according to any one of claims 1 to 14, characterized by the following additional steps:

Preferably simultaneous detection of the heart rate in addition to the determination of the rate of change of the blood vessel diameter;

Determining the Baroreflexsensitivität from the detected rate of change of the blood vessel diameter and the detected heart rate,

16. The method according to claim 15, characterized in that the heart rate is calculated from a simulated registered ECG,

17. The method according to any one of claims 15 and 16, characterized in that the heart rate and the rate of change of the blood vessel diameter are detected once at rest and once in a state in which the blood pressure in particular by a drug-induced provocation test or by physical or physical effects the patient is purposefully influenced and in particular increased.

18. The method according to any one of claims 15 and 16, characterized by the step: Detecting spontaneous blood pressure changes to determine baroreflex sensitivity

19. The method according to any one of claims 15 to 18, characterized by the step:

statistical evaluation of the determined measurement data for establishing a relationship between the rate of change of the bloodstream cross-section and the heart rate, in particular by determining regression curves.