EP0357690A1

EP0357690A1 - Device for non-invasive measurement of blood volume in human extremities

Info

Publication number: EP0357690A1
Application number: EP19890900797
Authority: EP
Inventors: Vladimir Blazek; Hans Schmitt
Original assignee: A Natterman und Cie GmbH
Current assignee: A Natterman und Cie GmbH
Priority date: 1987-12-30
Filing date: 1988-12-30
Publication date: 1990-03-14
Also published as: DE3744538A1; WO1989006108A1

Abstract

Un dispositif de mesure non-invasive du volume de sang dans les extrémités (UE) du corps humain comprend une balance (1) qui sert à mesurer le poids momentané de l'extrémité en question et se caractérise par une combinaison des caractéristiques suivantes: l'extrémité à examiner est posée sur un plateau (1a) de la balance; la balance (1) est un dispositif électronique de pesage dont le signal de sortie est fourni à une unité de commande et de calcul (3, 8) qui commande le déroulement de l'examen et qui prépare et fournit les valeurs mesurées du poids; on peut fournir un signal de correction à l'unité de commande et de calcul au moyen d'une unité d'entrée (3a), de façon à prendre en considération la position de l'extrémité examinée (UE) par rapport au corps de la personne (P); une fois l'extrémité posée sur le plateau de la balance, le dispositif de pesage mesure à de courts intervalles le poids de l'extrémité posée sur le plateau et ne commence l'examen proprement dit que lorsque les mesures du poids effectuées pendant une période déterminée donnent des résultats qui diffèrent de moins d'une valeur prédéterminable.A non-invasive device for measuring the volume of blood in the extremities (EU) of the human body comprises a balance (1) which is used to measure the momentary weight of the extremity in question and is characterized by a combination of the following characteristics: l the end to be examined is placed on a platform (1a) of the scale; the balance (1) is an electronic weighing device, the output signal of which is supplied to a control and calculation unit (3, 8) which controls the course of the examination and which prepares and supplies the measured values of the weight; a correction signal can be supplied to the control and calculation unit by means of an input unit (3a), so as to take into consideration the position of the examined end (UE) relative to the body of the person (P); once the end has been placed on the weighing pan, the weighing device measures the weight of the end placed on the pan at short intervals and does not begin the actual examination until the weight measurements have been made for a period determined results that differ by less than a predetermined value.

Description

Device for non-invasive measurement of blood volume in human extremities

Description

Technical field

The invention relates to a device for the non-invasive measurement of the blood volume in human extremities with a balance according to the preamble of claim 1.

Methods for determining the blood volumes of the lower extremities under selected physiological tests, such as e.g. Vein occlusion test, change of position test, muscle pump test. From the change in blood volume during these tests, important hemodynamic parameters can be defined, e.g. enable thrombosis detection or provide information about the function of the peripheral vessels (arteries, veins).

State of the art

Since HARVEY discovered the so-called large body cycle at the beginning of the 17th century, blood circulation has been one of the most widely studied Facts in human medicine. It has long been known that blood circulation obeys the laws of hydrodynamics. However, since blood does not represent Newtonian liquid and the blood vessels do not form rigid cylindrical tubes with a stationary laminar flow, Hagen-Poiseuille's law applies only with a simplified exception.

Furthermore, since the vessel radius is included in the fourth power of the equation, even a minimal change in radius has a clear hemodynamic effect.

Pathological processes in arteries and / or veins, such as vascular changes and occlusions (e.g. skierotic processes, venous thrombosis) must therefore show hamodynamic consequences due to the aforementioned physical relationships.

So far, a number of methods using different measuring principles have been developed to record peripheral hemodynamics. Above all, this includes X-ray contrast imaging - an invasive method that primarily enables topographically anatomical information. However, a number of non-invasive measurement techniques also belong to the prior art.

In particular, the qualitative method is skin temperature measurement or thermography and the semi-quantitative method: ultrasound Doppler technology, external electromagnetic flow measurement, external calorimetry, photoplethysmography (including light reflection rheography), impedance plethysmography to call. Only the so-called venous occlusion plethysmography is recognized as a qualitative, non-invasive procedure. Depending on the measuring principle used, it can be divided into

1.Water plethysmography (water displacement due to the volume change of the extremity, also called foot volumetry),

2. strain gauge plethysmography (change in resistance of the strain gauge as a result of the change in volume, also called straingauge plethysmography),

3. photogrammetric plethysmography (shadow change of the extremity due to the volume change, also called video plethysmography),

4. Gravimetric plethysmography.

The disadvantages of the methods mentioned under 1 to 3 are generally known, so they should not be discussed here. Of all the plethysmography processes known to date, the gravimetric method comes closest to real volumetry. As the name already suggests, the weight changes associated with the volume fluctuations of the extremity are recorded in this method.

So far, almost exclusively scales have been used for gravimetric plethysmography, which operate according to the two-pan scale principle. Both lower extremities were freely suspended in the air on a device. A sensor then transmits the force difference to a registration unit. In addition to the complexity of the measuring device, the disadvantages of this method can be seen in particular in the “keep balance” differential measuring mode used. The too narrow linear measuring range of this measuring principle, small resolution and low measuring accuracy, for example, have not allowed the relatively high initial weight of the leg and the small weight change due to, for example, the vein congestion to be recorded with the necessary accuracy.

A volume change method is also known in which the extremity to be examined is in a water bath. The amount of water displaced by the increase in volume is determined gravimetrically using a balanced balance. With this measurement variant too, attempts were made to circumvent the unfavorable relationship between high resting weight and small change in relativity. Various other disadvantages are associated with the use of this method. On the one hand the water bath causes a hydrostatic pressure on the skin and the tissue and this influences the blood accumulation in the skin veins, on the other hand the so-called perfusion pressure can be reduced from the increased pressure on the venous system. The influence of the skin's blood circulation by thermal stimuli in a water bath can hardly be excluded.

Presentation of the invention

The invention has for its object to develop a device for non-invasive measurement of blood volume in human extremities with a balance according to the preamble of claim 1 such that accurate statements about hamodynamic parameters are possible without the systematic measurement errors of the known devices. A solution to this problem according to the invention is characterized by its developments in the claims.

A solution to the problem is - as has been recognized according to the invention - only possible by combining a number of features:

On the one hand, the scale used is not a scale operating according to the two-bowl principle, but rather an electronic weighing device, on the weighing pan of which the extremity is placed, and the output signal of which is applied to a control and computing unit is that controls the course of the investigation and processes and outputs measured weight values. Such weighing devices are known with a measuring range of 0 to approx. 30 kg and a resolution of 1 g, so that their training need not be discussed in more detail at this point.

However, the sole use of the weighing technology known from other areas does not yet lead to the goal. According to the invention, it has been recognized that the unavoidable body movements of the person who is preferably lying or sitting examined require the output signal of the weighing device to be corrected. This correction takes into account, among other things, the shape of the leg position on the weighing pan, the specific weight of the blood and in particular the inevitable adjustment movements of the examined person until a quasi-static positioning process of the extremity on the weighing pan is achieved. For this purpose, the weight of the extremity is measured in short time intervals and the actual measuring process is only started when the weight measurements carried out within a certain time period are less than differ a predetermined weight value.

Advantageous developments of the invention are characterized in the subclaims.

Brief description of the drawing

The invention is described in more detail below on the basis of a few preferred exemplary embodiments and application examples with reference to the following drawings:

1 schematically shows a device according to the invention in a venous occlusion test and the patient positioning used therein,

Fig. 2 shows schematically the measurement curve in a venous occlusion test and another form of ^' leg position.

Fig. 3 different measurement curves in a vein occlusion test a) original curve b) filtered curve c) idealized curve

Fig. 4 shows an example of a computer protocol in a venous occlusion test

5 shows a schematic representation of the measurement signal in a combined positioning and muscle pump test,

6 shows an example of an original registration in a combined positioning and muscle pump test,

7 shows an example of a combination of the gravimetric and photoplethysmographic measuring principle. In all figures:

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows, schematically based on classic venous occlusion plethysmography with strain gauges, the patient positioning when performing the so-called venous occlusion tests.

In this test, the patient P lies on an examination table T, the limb UE to be examined (lower leg in the example shown) lies on the bowl 1a of the scale 1. The scale 1 is brought to the necessary height with a base 2 . The shell la is preferably made of a soft material and adapted to the anatomical shape of the lower leg. As a result, the largest possible storage of the extreme mität guaranteed so that in turn an unimpeded blood flow to the extremities is guaranteed. A tourniquet 6 is attached to the thigh. This leg position results in a "division" of the weight of the lower extremity between the scales and the knee joint / hip joint. Under these special conditions, the scale delivers a signal that corresponds to half the weight of the lower leg.

This signal is fed to a computer. The computer accepts the scale signal several times per second, corrects it by the above-mentioned positioning factor 2 and also takes into account other correction factors such as:

- the specific weight of blood, (necessary to convert weight / volume)

- The average specific weight of the lower leg (necessary to refer to the results in percentages by weight or volume).

The vein occlusion test is computer-controlled as follows:

After specifying the patient data and the shape of the leg position using the keyboard 3a, the current resting weight values are output on the monitor, either in numerical or curve representation, as desired.

The first measurement phase is carried out by pressing a start button at time A (see FIG. 2, here with a different form of leg support, which is very advantageous in practice)

I. During this phase, the measuring system checks the measuring signal until the patient is at rest (ie until a maximum difference of, for example, 50 g of two successive pairs of values is undershot over a period of 10 seconds). The computer therefore only releases another measurement when the patient is in an idle state. This is signaled to the examination person acoustically via loudspeaker 3c and optically via monitor 3b.

Now you can start phase II - automatic taring - by pressing the start button again at time B (see Fig. 2). The computer stores 20 weight values obtained at intervals of 1 second and uses this to determine the weight average of the stationary blood flow to the extremity. The measuring system then waits for the start command C to take the data from the test that follows.

After pressing the start button at time C (see FIG. 2), the examiner initiates the actual test phase III. This test phase preferably lasts 4 minutes. Immediately afterwards, with the help of the manometer system 7, a pressure is built up in the tourniquet 6 which is above the venous pressure. This dynamic pressure is preferably 80 mm Hg. Blood therefore flows into the extremity via the arterial system, but cannot flow away because of the venous congestion. In this purple congestion phase, which lasts, for example, 3 minutes, it is also called the occlusion phase, the blood volume increases in the extremity or the weight also directly. The examiner can monitor the weight gain on the monitor.

Preferably 5 seconds before the end of the stowage phase, the patient is prompted with acoustic signals during the not breathing for the next 15 seconds (Phase Illb). This prevents the respiratory fluctuations in the leg weight; this facilitates the later signal analysis. 5 seconds after the first tone there is a further signal (which is intended for the examinee and therefore preferably has a different pitch). Now the pressure in the cuff is released. The jammed blood can flow freely from the extremity. The emptying of blood is normally completed in a few seconds (so-called waterfall effect). In the case of a thrombosis, however, the kinetics are significantly prolonged during the emptying phase IIIc. The end of the respiratory pause is preferably signaled to the patient with a third tone.

The measurement is then ended automatically after 240 seconds. Now the measurement values are analyzed. Since these various circulatory fluctuations are subject (cf. curve a in FIG. 3), the curve can also be filtered (curve b in FIG. 3) or idealized by calculated kinetic functions (curve e in Fig. 3) are output.

Finally, various evaluation parameters of the venous occlusion test carried out are determined and the entire data set (measured values and results) is stored in a storage medium 4 and optionally also output to a printer 5. 4 shows an example of an examination protocol obtained in this way.

Depending on the positioning of the lower leg on the scale 1 (see FIGS. 1 and 2), the computer uses different factors for data correction. The information required for this (such as the angle of the lower leg / thigh, per size) via the keyboard 3a to the computer 3. In another embodiment of the measuring system according to the invention, the computer can also control the manometer system 7 directly and thereby fully automate the measuring process.

Fig. 5 shows schematically the application of the invention in a novel, combined positioning and muscle pump test. The blood drains from the lower leg while the leg is raised. Immediately after the change of position, the leg is kept still on the scales. The initial resting weight M rises slowly, since the leg fills with blood flowing "downhill" through the arteries. Important parameters of arterial blood flow to the extremity can be obtained from the kinetics of this filling. Phase B follows phase A. Now a leg movement program is carried out (eg 10 "accelerator pedal movements" within 15 seconds). Through this movement (muscle pump!) The blood is pumped out of the extremity "uphill" through the veins; the vein pressure drops, ie the leg weight also drops. Finally, in the last phase C (leg lies still on the scales), the leg fills up with blood again. If the venous system is intact, this filling phase C is relatively long. In the case of so-called venous insufficiency, this phase shortens considerably due to the pathological reflux in the leg veins themselves. Thus, the presented measuring device succeeds for the first time non-invasively, but directly quantifies the so-called muscle pump effectiveness. An example of this is shown in FIG. 6, registered on a recorder that was connected to the analog output of the scale 1. As mentioned, the device described detects the "integral" change in weight of the entire extremity (application also possible on the forearm). The method presented can also be expanded according to the invention by multi-channel photoplethysmographic scanning of the skin reflection in different leg floors (see FIG. 7). The scale provides a signal that is proportional to the total change in blood volume. From the relative change in the signals of the optical sensors S to S to one another, which can be detected by control electronics 8, possibly also controlled by computer 3, a statement can be made about changes in blood volume in the individual sensor areas of the leg.

Other areas of application for the described venous occlusion test are: Continuous monitoring of the patient in the event of a risk of thrombosis (e.g. during anesthesia in an operation), objectification of hemodynamically active medication, objectification of the so-called compression stocking therapy.

The methodology described is very easy to use, space-saving, inexpensive and, as already mentioned, completely painless and risk-free for the patient. Simple constructive features of the invention lead surprisingly simply to very meaningful and easily reproducible results.

Claims

Patent claims

1. Device for the non-invasive measurement of blood volume in human extremities with a balance with which the instantaneous weight of the respective extremity can be measured, characterized by the combination of the following features:

the extremity to be examined is placed on a weighing pan,

the scale is an electronic weighing device, the output signal of which is applied to a control and arithmetic unit which controls the course of the examination and processes and outputs the measured weight values,

a correction signal can be entered into the control and computing unit by means of an input unit, by means of which the position of the extremity to be examined is taken into account in relation to the body of the person,

- After placing the extremity on the weighing pan, the weighing device measures the weight at short intervals and does not start the actual measuring process until the weight measurements carried out within a certain period differ by less than a predeterminable weight value.

2. Apparatus according to claim 1, characterized in that on the respective extremity can be applied with a prescribable pressure Stauman¬ cuff, and that the instantaneous weight of the respective extremity is measured with and without a loaded cuff.

3. Device according to claim 1 or 2, characterized in that the control and arithmetic unit subjects the measured weight values to low-pass filtering.

4. Device according to one of claims 1 to 3, characterized in that the control and computing unit determines one or more functions from the measured weight values, which enable an exact assessment of the kinetics of the weight change.

5. Device according to one of claims 1 to 4, characterized in that the control and computing unit determines the weight of the extremity to be examined by averaging over a plurality of measured values before starting the actual measurement.

6. Device according to one of claims 1 to 5, characterized in that the control and computing unit for recognizing movements of the person to be examined, etc. compares the time profile of the measured weight values with certain stored signal profiles.

7. Device according to one of claims 1 to 6, characterized in that the control and computing unit recognizes the end of the measurement in that the weight measurements carried out within a certain time period differ by less than a predeterminable weight value.

8. Device according to one of claims 1 to 7, characterized in that the weighing device is a scale working with electromagnetic force compensation.

9. Device according to one of claims 1 to 8, characterized in that an acoustic output unit is provided which indicates to the examiner the start of measurement, certain measurement points and the end of measurement.

10. Device according to one of claims 1 to 9, characterized in that at least one optical sensor for optically determining the blood filling and emptying is additionally provided.

11. Device according to one of claims 1 to 10, characterized in that the input unit for da.s correction signal, by which the position of the extremity to be examined in relation to the body of the person is taken into account, is an optical sensor.

12. Device according to one of claims 1 to 11, characterized in that the weighing pan is adapted to the shape of the extremity to be placed.