LV13791B - Method and apparatus for noninvasive, continuous measurement of arterial blood pressure - Google Patents

Abstract

This invention relates to permanent and continued registration of blood-circulatory system parameters, particularly - for noninvasive, continuous measurement of arterial pulse by using noninvasive registration of function of the heart and arterial pulse, for example, electrocardiography and photoplethysmography, with following treatment of signals by determination of pulse wave distribution time (deltat) and photoplethysmogramm's pulsation amplitude (PPGPA) and calculation of arterial pressure values as maximal (ASmax), dynamical intermediate (ASav.dyn) as well minimal (ASmin) by using deltat and PPGPA and linear regression of pressure values bifactor coefficients characteristically for each person. The offered device for measurement of arterial pressure's noninvasive, maximal, dynamical intermediate and minimal value, that consists of pressure follow-on block and pressure calibration block, which their part consists from photoplethysmographical (PPG) optical signal contact sensor (11), electrocardiographical signal sensor (1), compression cuff (17), sound oscillation detector (12) for electronic amplifiers (2,10), which amplifies all of output signals, amplifying filters (3,9,13), which erase needless signal components, threshold detector (14), which detect sound tones, pump (19), which gives pressure in cuff, electrical valve (20), which reduces pressure in cuff, digital manometer (18), which control pressure in cuff, microcontrollers (4,16), which collect and analyzes data in accordance with described method, display (6) - for example, panel or monitor, which shows instantaneous values of ASmax, ASav.dyn. and ASmin and their dynamic in fixed period, keyboard (5), which provides interface with user, storage block (7), which maintain continuous measurement data, and sender (8), which provides telemetric pressure monitoring.

Description

The invention relates to the continuous and continuous determination and recording of circulatory parameters.

State of the art

Systemic arterial pressure (AS) is an essential parameter of the functional state of the circulatory system. AS pulsates with each pulse cycle, so it uses both extreme values of pressure over one cycle (maximum - AS _max and minimum - AS _m i _n ) and an imaginary mean value of non-pulsed pressure equivalent to the real variable pressure in a hemodynamic effect. pressure (AS _v id. dyn.) · AS _ma x represents the contractile force of the heart muscle, AS _m i _n - total hydrodynamic resistance of the peripheral blood vessels (arterioles), AS _v id. dyn. - Provides a quantitative summative assessment of hemodynamic function.

Control of arterial pressure is essential both for medical assessment of circulatory disorders and for preventive health examination or self-control; long-term non-invasive arterial pressure monitoring is also relevant in sports physiology to assess the ability of the circulatory system to adapt to exercise and to judge objectively the effectiveness of training or rehabilitation measures.

There are several ways of measuring both non-invasive (indirect) and invasive (direct) arterial blood pressure. Each type can have its own advantages and disadvantages that limit its use in one situation or another. The most accurate method of recording arterial pressure is the direct catheterization method, where a catheter attached to a manometer is inserted into the arterial artery. This method is traumatic and should only be performed by a highly qualified specialist. The direct measurement method is nowadays used only in extreme cases where obtaining an accurate pressure value is vital.

The quest for non-invasive pressure measurement dates back to 1834, when Herrison first applied the principle of back pressure. Later, Riva-Rochi improved the method by introducing air cuffs. Several years later, Korotkov developed a widely used auscultation method nowadays, which could also determine AS _m j _n . . A relatively recently introduced method for determining arterial pressure is the oscillometric method. Various modifications of the oscillometric method are already used in automatic pressure gauges already accepted as the medical standard (Clark et al. 1995).

The aforementioned methods use the so-called "cuff back pressure principle" - during measurement, the cuff is used to press the artery in the tissue and the pressure values are determined during the decompression period, when normal blood flow is restored (Pickering et al., 2005; Staessen et al., 1995). . Such methods do not allow continuous measurement of arterial pressure, and cuff pressure can cause discomfort.

Arterial pressure values (AS _ma x and AS _m j _n ) during each cycle can be determined using the Penaz finger cuff method (volume clamp method), which continuously maintains the pressure in the cuff to fully relieve the arterial wall (Penaz., 1973). . This principle is used in combination with the Wes.selinga physiocal algorithm in a Finometer ™ pressure recorder (Gizdulich P., Prentza A., Wesseling KH., 1997). For the time being, it is the only commercial device capable of non-invasively and continuously monitoring arterial pressure. However, its main disadvantage is that the subject is restricted in hand manipulation and prolonged finger compression can cause circulatory disturbances that cause discomfort; moreover, prolonged measurement is not possible due to impaired local blood circulation.

More convenient, simpler and more widely used methods may be those that use arterial pressure parameters to calculate arterial pressure, which are completely atraumatic, non-invasive, and unobtrusive to the subject. One such parameter could be pulse wave propagation (delay) time (At), or derived from it, the pulse wave propagation rate (PWV).

Several attempts have been made to use pulse wave delay time for pressure determination (Golub., 1995; On., Et al., 1989, US 5865755A). In this type of method, the critical step is the calibration needed to obtain the typical pulse-wave delay time-arterial pressure relationship characteristics of an individual. Theoretically, this relationship requires at least two arterial pressure measurements that differ by at least 20mmHg. To avoid single calibration, a statistically large slope of the regression curve (linear regression coefficients) of a large population is used (Orr., Et al., 1989). In this case, to construct the curve, it is sufficient to measure arterial pressure only once (eg, at rest, under conditions) by simultaneously taking photoplethysmograms and cardiograms to determine the pulse wave delay time. The method gives relatively accurate measurements at rest, but the pressure values obtained in this way during physical activity are very different from the real ones. There are attempts to improve this method. For example, the differential pressure value required to determine the regression relationship is obtained by varying the height of the limb relative to the level of the heart (Willshire RJ, 2004). This method, too, is not accurate enough, because the artery through which the pulse wave propagates produces a gradient of pressure and tension of the artery wall. Methods for measuring pressure at the amplitude of a photoplethysmographic signal have been developed by combining photoplethysmogram recording with the Penaza volume clamp method and taking into account the position of the limb relative to the heart level (Asada. Et al., 2007).

Disclosure of the Invention

The object of the invention is to increase the reliability of the signals used for the calculation of arterial pressure (AS), to increase the accuracy of the determination of arterial pressure values and to provide more convenient measurement.

To achieve this goal, two relationships are used: the functional relationship between arterial pressure and pulse wave propagation time, which is directly proportional to the pulse wave propagation speed, and the dependence of the shape of the ripple curve on the photoplethysmogram on arterial pressure reflecting the viscoelastic properties of the circulatory bed. Allen et al., 1999). Methods to calculate arterial pressure values using arterial pulse wave propagation time or pulse wave propagation velocity as determined by recording vascular pulsations in peripheral tissues of the body are already known (Kazanavicius et al., 2003; Golub., 1995).

The relation between arterial pressure and pulse wave propagation velocity is formally expressed by the Moena-Kortevega equation:

PWV =

E-h 2-r p where E - modulus of elasticity of arterial wall, h - thickness of arterial wall, r - radius of artery, p - blood density.

Pulse wave propagation velocity (PWV) in arteries is mainly dependent on their wall elastic modulus (E). As arterial pressure increases, the wall of the arteries is stretched more and its elasticity decreases, while the velocity of the pulse wave propagates. As pressure decreases, the opposite occurs (Smith., Et al., 1999). The arterial wall tension caused by arterial pressure also influences other determinants of the pulse wave propagation rate included in the Moena-Kortevega equation - arterial wall thickness (h) and inner radius (r). As the pressure increases, the wall thickness decreases and the inside radius increases. The effect of blood density (p) on the pulse wave propagation rate is negligible because of its relatively small range of variability under normal conditions.

Arterial pressure values fluctuate in a wavy fashion, corresponding to cardiac cycle phases, respiratory phases, and other changes in vasomotor activity.

The results of a series of clinical measurements (23 practically healthy subjects, AS, At, and PPGpa measurements at 23 ± 2 ° C before and after exercise) show a relationship between these three parameters, which can be approximated by a two-factor linear regression model y = a + biXi + b2X2, where Xj and Χ2 are the arterial pressure values. The regression coefficients (a and b) for this relationship are specific to each individual and to the vascular bed.

Regression coefficients for a given curve can be obtained by recording the pulse wave delay time and the amplitude of the pulse curve at two different pressure values of at least 20 mmHg (calibrated). Coefficients derived from the calibration process are used to calculate pressure values for further investigations.

The process of calibrating arterial pressure and calculating blood pressure according to the present invention is carried out as follows. An ECG sensor is placed on the subject's chest. A photoplethysmographic (PPG) optical signal contact sensor is attached to the subject's external ear shell. A compression cuff with a built-in sound-level detector is placed on the upper arm of the subject's left arm and the hand is placed at the person's heart level. The auscultation method measures arterial pressure (AS _max and AS _m i _n ) at rest by simultaneously recording ECG and PPG signals at the time of pressure measurement. The subject shall grasp the hand dynamometer with his right hand. The cuff placed on the left hand produces a pressure greater than twenty mmHg greater than the measured AS _ma x · After a specific sound or light signal, the subject squeezes and holds the hand dynamometer as far as possible. The PPG and ECG parameter values in the cycle at which the sound detector begins to sense the first sounds of arterial origin are stored for later calculations. The cuff pressure is then rapidly reduced until any arterial sound in the detector disappears; the corresponding values for PPG and ECG parameters as well as arterial pressure are maintained. After completion of the calibration, a compression cuff with a built-in sound vibration detector is removed from the subject's left hand. Using two different blood pressure values and their corresponding PPG ripple amplitude and delay time values, the two-factor linear regression model produces regression coefficients (a; bj; b ₂ ). In the following, the instantaneous AS values for a particular subject are calculated using only instantaneous pulse wave propagation time and pulse wave curve amplitude values, and two-factor linear regression coefficients from the previous calibration. The calculated arterial pressure values to increase the reliability and accuracy of each subsequent pressure value are calculated by averaging the 3 preceding and 3 subsequent instantaneous values.

The method and device for non-invasive and continuous determination of arterial blood pressure is explained in the accompanying drawings.

a brief description of the drawings

FIG. 1 is a block diagram of a non-invasive and continuous device for measuring blood pressure;

FIG. Fig. 2 is a schematic diagram of pulse wave propagation time and pulse amplitude of a photopletismogram;

FIG. Figure 3 is a diagram of sensor placement during arterial pressure calibration and measurement.

FIG. The non-invasive and continuous arterial pressure measuring device shown in Figure 1 comprises two functional blocks, a pressure monitoring unit and a pressure calibration unit, which in turn consist of two functional units, the pressure monitoring unit and the pressure calibration unit, which in turn consist of a photoplethysmographic (PPG) optical signal contact sensor. 11), electronic amplifiers (2, 10) for electrocardiographic (ECG) signal sensor (1), compression cuff (17), sound oscillation detector (12), amplifying all output signals, amplifying filters (3,9,13), extinguishes unnecessary signal components, microcontrollers of a threshold detector (14) that receives sound tones, a pump (19) that generates cuff pressure, an electric valve (20) that reduces cuff pressure, a digital manometer (18) that controls cuff pressure ( 4, 16) who perform data collection and analysis according to the method described, display (6) - such as a panel or monitor that displays AS _ma x, AS _V id. dyn. and AS _m j _n instantaneous values and their dynamics over a period of time, a keypad (5) providing an interface to the user, a memory unit (7) storing continuous measurement data and a transmitter (8) providing telemetric pressure monitoring.

Pulse Wave Propagation Time (At) - FIG. 2 measured as the distance from the tip of the R wave of the ECG to the "foot" of the pulse wave (the lowest level of the PPG signal), the amplitude of the photoplethmogram ripple (PPGpa) measured as the distance

Exemplary embodiment of the invention

The subject is a 27-year-old male. The subject is put on his ear

PPG contact sensor and ECG electrode strap. A calibration unit is attached to the pressure gauge and an air compression cuff with a sound-level detector is placed on the upper arm. At the first measurement, the auscultation method measures arterial blood pressure (AS _max i = 100 mmHg; AS _m j _n i = 60 mm Hg) and simultaneously determines the corresponding Ati and PPGpa values (Ati = 0.1320s; PPGpAi = 3.86rv-ankle-upper arm index) conditions. A second time, the same values (AS _max 2 = 130mmHg; AS _m in2 ⁼ 70mmHg; At2 = 0.1212s; PPGpA2 ⁼ 2.51rv) are determined during static loading (with hand dynamometer). The subject shall remove the air-compression cuff and sound-level detector and disconnect the calibration unit from the recording equipment. Using the AS, At and PPGpa values, calculate the coefficients of the linear two-factor regression equation (AS _max = 670- (4817 * At + 16.63 * PPGpA);

AS _m i _n = 331- (2404 * At + 11.75 * PPGpA), which are further used for non-invasive calculation of AS values for this individual. The average dynamic pressure value is obtained from the AS and AS _{max m} j _n values the given correlations AS _v id. dyn. ⁼ [(2 * AS _m j _n ) + AS _max ] / 3. After registering the first six cardiac cycles, all three mean values of pressure are displayed.

The proposed method, compared to other methods that use pulse wave propagation time or velocity information to calculate arterial pressure, is more convenient to use, pressure calibration is faster, and the mode of pressure change is physiological (limited volume and intensity, fully atraumatic load); it is possible to perform telemetric pressure measurement, as the proposed equipment is capable of storing and transmitting measurement data over a wireless communication channel in real time. Determining the mean values of the pressure included in the method reduces the occurrence of artifacts, thus improving the accuracy of measurement.

Sources of information:

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3. Clark Justin. Total compliance method and apparatus for noninvasive arterial continuous blood pressure monitoring method and apparatus. - International PatentUS 5423322, 1995.

4. Gizdulich P., Prentza A., Wesseling KH. Models of brachial to finger pulse wave distortion and pressure decrement. Cardiovascular Research. 33 (3): 698705, 1997. Mar.

5. Golub H .., Method and apparatus for non-invasive, cuffless continuous blood pressure determination. - United States Patent US005857975A, 1999.

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Arterial Blood Pressure Using the Pulse Transit Time. - Information Technology and Management, 4 (29): 23 - 29.

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Claims

Claims (10)

Claims 1. A method for non-invasive and continuous determination of arterial blood pressure using an ECG signal and an arterial pulse signal from peripheral tissue of the body. 5 distance from tip of ECG R wave to a given point in PPG curve (At) and calculation of pulse amplitude (PPGpa) of PPG curve from At and PPGpa, reduction of artefacts differing in that obtained pressure value (AS _max ., ASvid. din., AS _m in) for increasing accuracy and reliability, the pressure value is calculated by averaging and the pressure value is independently 10 calibrations. The method of claim 1, wherein the distance from the tip of the R wave to the onset of the footprint of the PPG curve (At) and the peak value of the pulse amplitude of the PPG curve (PPGpa) are used to calculate arterial pressure. Method according to claim 1 or 2, characterized in that the calibration is carried out by double recording the AS _max ., The AS _m j _n pressure values simultaneously with the respective (At) and PPGpa values, wherein for the first time the AS is measured with auscultation method at rest. ^20th Method according to any one of claims 1 to 3, characterized in that the second pressure recording of the calibration is performed by applying a pressure of at least 20 mmHg higher on the compression cuff than the AS _max obtained during the first measurement during calibration. Method according to any one of claims 1 to 4, characterized in that the calibration secondary pressure is determined under static load using a hand-held dynamometer. 30th Method according to any one of claims 1 to 5, characterized in that, during calibration, the secondary pressure value, AS _ma x, is read at the time when characteristic sound signals appear on the pressed artery. A method according to any one of claims 1 to 6, characterized in that, during the calibration secondary pressure recording, the AS _m in value is determined by rapidly decompressing the cuff immediately after the determination of the AS _max , at the time of disappearance of p. the sounds mentioned. The method of any one of claims 1 to 7, wherein two-factor linear regression coefficients AS _max ., ASmin are calculated during calibration. value for relation to (At) and PPGpa values. A method according to any one of claims 1 to 8, characterized in that the instantaneous values of arterial pressure AS _max ., AS _m j _n are calculated by averaging the 3 preceding and 3 subsequent values and the mean dynamic arterial pressure. the instantaneous value is obtained from the calculated instantaneous pressure values as a function of AS vid, dyn. ((2 ASmin) ū AS _m ax] / ^J · 1Q. A device for noninvasive and continuous determination of arterial pressure, comprising: - a pressure tracking unit consisting of a photoplethysmographic (PPG) optical signal contact sensor (11) for electronic output signals; 20 amplifiers (2, 10), amplifier filters for clearing unnecessary signal components (3, 9), microcontroller (4) for data acquisition and analysis, display (6) showing AS _max , AS _V id. dyn. and AS _m i _n instantaneous values and their dynamics over a period of time, telemetry of the keypad (5) for user interface, memory unit (7) and transmitter (8) 25 for pressure monitoring and - a pressure calibration unit consisting of a compression cuff (17), a sound oscillation detector (12) for amplifying a filter for clearing unnecessary signal components (13), a threshold detector for receiving sound signals (14), a pump (19), an electric valve (20). for cuff pressure relief, digital 30 manometer (18), microcontroller (16). A device according to claim 10, characterized in that it comprises a telemetric transmitter for transmitting the measurement data.