EP0403522A1

EP0403522A1 - Method of continuous measurement of blood pressure in humans

Info

Publication number: EP0403522A1
Application number: EP89903093A
Authority: EP
Inventors: Waldemar Greubel; Albrecht A. C. VON MÜLLER; Hubertus Von Stein; Rudolf Wieczorek
Original assignee: Vectron Gesellschaft fuer Technologieentwicklung und Systemforschung mbH
Current assignee: Vectron Gesellschaft fuer Technologieentwicklung und Systemforschung mbH
Priority date: 1988-03-09
Filing date: 1989-03-09
Publication date: 1990-12-27
Also published as: JPH03505533A; DE3807672A1; DE3807672C2; US5237997A; WO1989008424A1

Abstract

Selon un procédé de mesure en continu de la tension artérielle, la tension artérielle moyenne est déterminée sur la base de la durée de propagation des ondes du pouls. Les autres paramètres de la tension artérielle sont obtenus en combinaison avec une mesure optoélectronique de la densité volumétrique du sang effectuée de manière typique sur le lobe de l'oreille. On part d'un étalonnage de base individuel des valeurs de la tension artérielle obtenues par un procédé conventionnel. Des étalonnages ultérieurs automatiques continus sont effectués par des moyens optoélectroniques. On utilise de préférence comme capteurs de mesure des clips d'oreilles (10) et des électrodes d'ECG (16) ou des capteurs photoélectriques. Ce procédé s'applique surtout en médecine préventive et pour des diagnostics.According to a continuous blood pressure measurement method, the average blood pressure is determined on the basis of the pulse wave propagation time. Other blood pressure parameters are obtained in combination with an optoelectronic measurement of volumetric blood density typically performed on the earlobe. One starts from an individual basic calibration of the blood pressure values obtained by a conventional method. Continuous automatic subsequent calibrations are performed by optoelectronic means. Ear clips (10) and ECG electrodes (16) or photoelectric sensors are preferably used as measuring sensors. This method is mainly used in preventive medicine and for diagnostics.

Description

Method for continuously measuring human blood pressure

The invention relates to a method for the continuous, non-invasive measurement of blood pressure in humans.

All known, practically usable, non-invasive blood pressure monitors use in a modified form the measuring method according to Riva-Rocci / Korotkoff (RR method) or instead of Korotkoff microphones, the oscillation of the pressure in an elastic cuff. This applies both to manual operation and to automated devices that. are offered as outpatient blood pressure monitors with 24-hour measurement. The main disadvantages of such blood pressure monitors, which can in principle also be worn on the body, are that, due to the repeated interruption of the blood circulation, they are very uncomfortable for the patient in the long run and that the long time interval between the measurements caused thereby does not permit continuous measurement.

It is also known that the pulse swell speed allows a certain access to blood pressure. When measuring the pulse wave velocity or pulse wave transit time (PWL), the transit time of the pulse wave caused by each heartbeat is measured, either using the time difference between the R wave of the electrocardiogram (EKG) and the arrival of the pulse at a peripheral artery measures or the time difference between two different distal pulses via mechanical or optical Sensor recorded. The thus determined pulse transit time correlates intraindi vidually high with average Blutdruckwer¬ th. The Hauptnachtei of this method is that a measurement of the separated ge ^¬ di Astol regard and systolic pressures is in principle not possible.

Furthermore, there are measuring devices on the market which only determine the changes in the amount of blood on the earlobe fluctuating with the pulse in a photoelectrical manner, qualitatively and roughly, so-called ear pulse measuring devices (OPM). These devices, which have been known in principle for a long time, only serve to determine the pulse frequency.

Other suggestions for non-invasive, continuous blood pressure measurement that make use of placing a sensor immovably exactly over a single artery (e.g. arm artery) practically fail due to the much too large sensor! ictikeit against movement artifacts.

Although the human blood pressure is one of the most important dimensions on the physiological scale and is of great importance in the preventive area, in diagnostics and in per- and postoperative monitoring, the problem that exists in all of these areas is: Measure blood pressure continuously and bloodlessly.

The object of the invention is therefore to provide a blood pressure measuring method with which the blood pressure can be measured continuously and without blood with the required accuracy, in particular the systolic, diastolic and mean blood pressure. Another object of the invention is to avoid the above-mentioned disadvantages of the known measuring devices based on the RR method. The problem of sensitivity to movement artifacts should also be solved. This object is achieved essentially by the method defined in claim 1. Before ^¬ part refinements of the invention result from the subclaims.

Blood volume density in the sense of the present invention is to be understood as the blood volume per unit volume of tissue in a body tissue with a dense blood vessel network (e.g. earlobe) that changes periodically with the pulse rate and is influenced by the body's own regulations.

The main advantages of the invention are that a continuous, non-invasive blood pressure measurement is possible not only in the clinic, but also in the everyday environment, even in the state of the head, that the sensors, namely ear clip and EKG, electrodes for Patien¬ th too vernachl ssigende physical impairment represent that the measuring system easily portable on the body is because it is very small and light that the system has reduced to a ^'minimum susceptibility to motion artifacts, because not is measured on a single artery and that the measuring system is considerably cheaper to produce than systems according to the prior art.

In principle, all pulse-registering measuring systems can be used as the ear pulse measuring device sensor for determining the arterial blood volume density proportional to the blood pressure, in which a measuring signal taken from the earlobe is proportional to the blood volume density and / or the blood pressure.

In principle, all well-perfused areas of the skin can be used as a measuring point for the arterial blood volume density, of course the acral areas of the skin (fingers, toes, earlobes) are particularly suitable for attaching sensors. To switch off the influence of the variable oxygen saturation of the blood on the ear pulse measuring device detector signal, an IR light wavelength length X is preferably chosen, which ^* results from the crossing point of the spectral transmission for reduced and oxygenated blood, the so-called i sobesti see point (e.g. λ = 805 nm).

In cases where the pulse swell time determination with the aid of the EKG electrodes leads to unsatisfactory results, a suitable miniature microphone is used instead of the EKG electrode, which is attached with an adhesive strip over the heart. The microphone then serves to determine the systole (first heart tone).

Instead of using ECG electrodes or a miniature microphone as a reference sensor for detecting the pulse wave near the heart, a particularly preferred further development of the invention can also include an LED and photodiode to be attached to certain areas of the chest or back near the heart Use sensor. In analogy to the ear pulse measuring device sensor, the light of the LED is scattered on the fine blood vessel network, the scattered light is registered by the photodiode, and thus the exact time at which the pulse wave passes the sensor. It is crucial that the area of skin on which the sensor is attached is supplied with blood from an intercostal artery as close as possible to the heart. For this sensor close to the heart, the location on the chest or back should be selected, taking into account the anatomical course of the vessel, so that the duration of the pulse wave from the heart to the sensor close to the heart is minimized, thus maximizing the time difference between the pulse wave between the sensor near the heart and the ear pulse sensor. This preferred embodiment is particularly precise and is not particularly prone to failure.

An additional possibility to further reduce movement artifacts, but also other disturbances, is to use both earlobes with one ear pulse measurement device. By comparing the signals coming from both earlobes, for example using a coincidence circuit, many types of interference can be eliminated.

In the following an embodiment of the invention will be described with reference to the drawing. The drawing shows:

1 is a graphical representation of the time course of the output signal of the ear pulse measuring device of the blood pressure measuring device operating according to the method according to the invention,

2 shows a schematic illustration of the blood pressure measuring device operating according to the method according to the invention, and

3 shows a section through the ear clip of the blood pressure measuring device according to the invention in a semi-schematic representation.

On the patient's chest, (two) ECG electrodes are attached above the heart. The ear pulse measuring device sensor is clamped or additionally glued to the earlobe with an ear clip. The ear pulse measuring device sensor fulfills a double function: a small light source with a suitable wavelength shines through the earlobe. The transmission of the earlobe, which varies proportionally with the blood pressure, is measured by a photodiode. The arrival of the pulse wave at the earlobe, registered relative to the systole by the EKG signal, can also be seen directly from the transmission timing. This determines the pulse wave transit time for the heart / earlobe segment.

An individual calibration curve is created for each patient before the start of the continuous measurement, which curve shows the relationship between the pulse wave transit time and the associated mean Blood pressure p indicates, determined according to the well-known ^{• •} ³ cuff method. Since this relationship is almost linear, about three measuring points are sufficient for the display, corresponding to the same number of required K-rei sl on load stages in the calibration

For further explanation, FIG. 1 shows schematically the course of the photocurrent i (t) on the ear pulse measuring device photodiode, the light source in this example being a pulsed (infrared) light-emitting diode. The associated blood pressure values are shown on the right edge of the figure (mean p, systolic p „and di astolic pressure p.). In the ^r m ^{J r} s α

Practice applies:

Pm ⁼ Pd ^{+ f * (} Ps ^" Pd ^} (Equation 1)

where f = 1/3 generally applies to peripheral arteries. In case of doubt, f can easily be determined specimen-specific. -

Since according to equation 1 between the three blood pressure parameters p, p and p. in practice there is a linear relationship, it becomes clear that the pulse swell enl time PWL at calibration ³ alternatively either pm, p ^r s "or p ^r d. can assign.

In any case, it should be noted that only one of the two independent blood pressure variables can be obtained by measuring the pulse wave transit time. The second independent blood pressure value is determined as follows with the aid of the photocurrent curve of the ear pulse measuring device.

Consider the envelope of the photocurrent signal i (t) in Fig. 1. In this, the signal difference Δi corresponds to the blood pressure difference Ap = p _s - p. At the beginning of the blood pressure measurement, one measures according to the Riva-Rocci method p and P _d in a specific one Time, then i can be assigned to Δp, ie the photocurrent curve can be converted into blood pressure values for a limited period of time (at least for a few seconds) and at the same time the blood pressure scale (Fig. 1 on the right) can be permanently changed Zero point establish. But since by vasomotor and other body's regulations assigning photocurrent value to blood pressure value over Zei ^'t change Erfin done dung as an automatic recalibration of this association by, for example the ongoing aufzei swell enl about the Pul t be ^¬ voted worth p, used to follow up the photocurrent curve in blood pressure values, so that the systolic blood pressure can then be read directly from the photocurrent value belonging to p ^' . An analogous procedure can be used if, alternatively, the pulse pressure p or p in the sample-specific calibration curve has been assigned to the pulse swell enl over time. Equation 1 can be used to calibrate the photocurrent curve of the ear pulse measuring device into blood pressure values.

The above-mentioned ongoing re-calibration, carried out automatically by electronic means, is necessary for the following reasons:

In the dense arterial vascular system of the earlobe, signal changes .DELTA.i can typically be caused firstly by blood pressure-proportional pulse-synchronous vasodilatation and secondly by slow vasomotor and other changes in the amount of C-apillaries through which flow occurs.

If e is the extinction of the IR light (sum of absorption and scattering), q (t) the pulsating cross-section of the vessel and ⁿ Ca _D ^{the men} 9 ^{e of the} capillaries, ^which sometimes carry blood, then the following proportionality applies: e <v> q (t) • n ~. n ~

Cap cap is changing slowly. Changes in n _c are taken into account by the automatic re-calibration mentioned. The block diagram in FIG. 2 illustrates the structure of the blood pressure measuring system, wherein one can be content with a sketch of the signal paths between the components and details can be left to the person skilled in the art.

This comes from the ear pulse measuring device 10 in FIG. 1 sketched signal i (t) in the analogue digital wall! he 12. The digitized signal goes for processing in the microcomputer 14. The AD converter 12 receives control signals from the microcomputer 14. In addition, the microcomputer 14 also controls all signals emanating from the ear pulse measuring device 10. The signals from the reference sensor 16 for detecting the start of the pulse wave (symbolized in FIG. 2 as an EKG signal) go directly to the microcomputer 14. In addition, the sample-specific calibration curve is input to the microcomputer 14 via the line 18 and the calibration curve is in the micro ¬ computer 14 stored (in Fig. 2, the case was chosen that the pulse wave transit time was determined as a function of p ^r m). This calibration curve is used by the microcomputer for the ongoing conversion of the pulse wave transit times into the respectively selected blood pressure size. In addition, a further task of the microcomputer 14 is sketched in FIG. 2, namely the automatic re-calibration of the photocurrent curve in blood pressure values at 20.

An exemplary embodiment of an ear pulse measuring device sensor in the form of an ear clip is shown in section in FIG. 3. Therein 1 denotes an LED, 2 a photodiode and 3 an integrated temperature sensor. The clamped ear clip is well fixed on both sides of the earlobe 5 with the help of ring-shaped adhesive strips 4. The temperature sensor 3 is in skin contact with the earlobe. The temperature measurement is used for the additional control of changes in the blood volume density of the earlobe, which have to be continuously monitored as described.

Claims

Expectations

1. A method for continuously measuring human blood pressure, characterized in that

that to determine one of the three blood pressure values (systolic, diastolic or mean blood pressure) the pulse wave transit time is measured continuously, use being made of a subject-specific calibration curve which shows the pulse swell enl as a function of blood pressure used indicates

that the arterial blood pressure proportional blood volume density is continuously determined with an ear pulse measuring device which is attached to the earlobe of the test subject,

that the ear pulse measuring device is used simultaneously for measuring the pulse wave transit time, and

that the measurement signal of the ear pulse measuring device is continuously re-calibrated electronically to take into account vasomotor and other body-specific regulations.

2. The method according to claim 1, characterized in that the re-calibration takes place in that the associated measurement signal is registered at certain constant blood pressure values and a correction of the blood pressure values is made from the change thereof.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that before the start of the continuous blood pressure measurement according to the Riva-Rocci method, the systolic and diastolic blood pressure are measured, from this the pressure difference Δp is calculated and this pressure difference Λp the difference Δi of the output signal corresponding to the di astol i value and the output signal of the ear pulse measuring device corresponding to the systolic value is assigned.

4. The method according to any one of the preceding claims, characterized in that for recording the sample-specific calibration curve before the start of the continuous blood pressure measurement, the pulse wave transit time is measured as a function of several blood pressure values.

5. The method according to any one of the preceding claims, characterized in that a photoelectric sensor is used to measure the pulse wave running time, the near the heart on a skin area on the chest or the back of the subject, with a near-heart intercostal species ^* e Blood is supplied, is attached.

6. The method according to any one of claims 1 to 4, characterized in that EKG electrodes above the heart are used to measure the pulse swell enl time.

7. The method according to any one of claims 1 to 4, characterized in that for measuring the pulse swell enl time a miniature microphone for registering the first heart tone is attached to the heart.

8. The method according to any one of the preceding claims, characterized in that a pulsed infrared light-emitting diode is used to irradiate the ear lobe and that the transmission of the ear lobe is measured by a photo diode.

9. The method according to claim 8, characterized in that in order to avoid the influences of the variable oxygen saturation of the blood for the infrared light-emitting diode, an IR wavelength in the vicinity of an i sobesti see point is selected.

10. The method according to any one of the preceding claims, characterized in that both ear lobes are each provided with an ear pulse measuring device t and that the measurement signals of the two pulse measuring devices are compared electronically in order to eliminate different types of interference.

11. The method according to claim 10, characterized in that the two measurement signals are fed to a coincidence circuit which suppresses all signals which are not measured simultaneously on both ear lobes, and thus evaluates them as artifacts.

12. The method according to any one of the preceding claims, characterized in that the body temperature is continuously measured at the earlobe and the measurement signal of the ear pulse measuring device is corrected as a function of the measured temperature.

13. Blood pressure monitor for performing the method according to claim 12, characterized in that the ear pulse sensor to be attached to the earlobe contains an integrated temperature sensor (3) which is in skin contact with the earlobe (5).