NZ539983A - Cuffless continuous blood pressure and blood pressure wave velocity monitor - Google Patents

Abstract

A cuffless (in the sense that a pressurized upper arm cuff is not required) portable monitor for the continuous measurement of blood pressure, pulse rate and pulse wave velocity includes a pair of capacitative sensors 1, 2 located above the artery in the lower arm at a predetermined distance from each other. The time separated signals from the capacitative sensors that are generated in the sensors at each arterial pressure pulse are converted into pulse width modulated signals by integrated circuit 5 and digital signals indicative of the blood pressure, pulse rate and pulse wave velocity by the microprocessor 6.

Description

539 SO 3 Cuffless continuous blood pressure and blood pressure wave velocity monitor.

I ALEXEI SIVOLAPOV , of 48A Raukawa St., Strathmore, Wellington, New Zealand, a New Zealand Citizen.

HEREBY declare the invention, for which I prey that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of and apparatus for continuously measuring arterial blood pressure, pulse wave velocity and pulse rate.

One of traditional indicators of the condition of the human body is cardiovascular pulsation. Different cardiovascular diseases can be diagnosed depending on the shape, amplitude and rhythm of the pulsation. It is veiy important that the parameters of the cardiovascular system are read out continuously while patient is active.

However, meantime most monitors for continuously measurement those parameters can operate only in ambulatory conditions.

One kind of monitors utilize a pressure gauge and an inflatable cuff, which terminates the flow of blood through an artery during the measurement process, as result the measurement cannot be used for continuously measurement.

Other kind of monitors utilize noninvasive devices such as finger photoplethysmographs and electrical impedance plethysmographs. Transducers of these monitors generate a very weak signal, which requires a lot of electronic hardware. In result these devices being too cumbersome and expensive. They can only be used in laboratory condition.

Russian patent No 20402207 (Sivolapov) discloses a device for measurement blood pressure and capacitive sensors for that. The two capacitive sensors placed over the radial artery on fixed distance. By means of the sensors and converting system define time of a travel of the pulse wave from first to second sensors and then calculate the value of the blood pressure. The result of the calculate is shown on the display.

Unite Stats patent No 4,245,648 (Gordon) present a measurement system comprising means to coupled exteriorized artery at first and second location converting system which measure the rise time each of the first and second wave forms. The rise time measuring means and to the transit time measuring means computers the systolic pressure, diastolic pressure and pulse rate corresponding to each pulse pressure wave.

The present invention suggests a method and an electronic measuring system which measures arterial blood pressure, pulse wave velocity and pulse rate. The device can be easy realized in portable construction for a monitoring people when they have exercises or some work to do. i FIG.l indicates the general configuration of the monitor on a wrist.

FIG.2 illustrates the locations of sensors where they relating to the radial artery and how distance L is defined.

FIG.3 indicates the general construction of the capacitive sensors.

FIG.4 gives more detail and definition reference to the shape of the membranes' sensors. FIG.5 displays the simple construction of capacitive sensors.

FIG.6 shows a graphed example of a blood pressure wave and which part of the wave is measured. FIG.7 shows how the pulse width modulator works and how its signal is converted to digital code. FIG.8 is a block diagram showing the basic electronic elements of a preferred embodiment of the present invention.

FIG.9 explains how a time propagation pulse wave from first to second sensors is defined.

In order to better illustrate the advantages of the invention and its contributions to the design, the theory and operation of the present invention will be discussed and then a preferred hardware embodiment of the invention will be described in some detail.

In most cases best place to use the device on the radial artery is the wrist, like shown the wrist in the human hand offers a fascinating location for a noninvasive measurement device. There are both physiological and practical reasons, which make the wrist for measurement purposes. The main arteries in the wrist, especial the radial artery, are close to the skin surface and continuous pulsation can be easily detected.

Fig.l shows 1 and 2 are the first and second sensors. Under the sensors radial artery 3 locate. All parts of the monitor fixed on the wrist by means of the strap 4. Closely to sensors 1 and 2 the converter 5 is fixed, which converts value of capacitive sensors to digital information and send it to the module of the microprocessor 6. In this module pulse wave velocity, systolic, diastolic blood pressure and pulse rate are caculated. The values of those parameters are displayed by means of the display module 7. In the microprocessor 6, information is acquired about the cardiovascular pulsation parameters in radial artery from 1 and 2 sensors and fixed parameters (for example means of a distance between sensors), which are set by the user before that, to start measurement. These fixed parameters is set by means of the special module 8 "set up" which is connected to the microprocessor module 6 by use the cable 9, connector 10 and 11. Module 8 can be used like interface between the blood pressure monitor and the computer system or personal computer. For that, a standard USB connector can be used.

Fig.2 gives more details, how first 1 and second 2 sensors are fixed by strap 4. Pulse pressure wave travel in the direction, as shows on Fig.2. This wave generates a force F, which impacts sensors 1 and 2. Special plate 14 is fixed on the top membrane of the sensor and the bugle 15 is fixed on the bottom membrane of the sensors. Those plate and bugle need to concentrate the force, which is generate by the pulse pressure wave of the radial artery on at the center of the membranes. The result is that wall of the radial artery creates a bigger impact on the sensor which make more sensitive.

On Fig.3 the construction of the capacitive sensor that is used for a converting a blood pressure pulse wave to the variation of the electrical capacitive of the construction. The construction consists the elastic n-membranes, which are fixed on their ends (For example to stick dielectric glue). The membranes are made from any elastic materials, but the both surfaces of the membranes must have very good electrical conductivity. Sensitivity depends on the sizes and thickness of the membranes a it is shown on Fig.5. Combine the size of the membranes get necessary mechanical sensitivity of the capacitive sensors.

Fig.4 "A" and "B" illustrate that by means of a variations in shape of the membranes' surface, different characteristics and sensitivity of sensors can be achieved as well.

Fig.5 shows simple construction of the capacitive sensor and clarifies how these sensors operate. When pulse pressure wave goes through the radial artery, it generates force F, which squeeze into membranes of the sensor proportional to blood pressure in radial artery. Electric capacitive of this construction changes according to blood pressure. Thus a value of a capacitive of the sensor is reflected in pulse pressure waveform. By means of wires the sensors are connected to electronics circuit.

Blood pressure pulse wave is well known to look as shown on Fig.6. This figure shows that the pulse pressure wave reaches sensor 2 with a delay x, because the pulse pressure wave has a pulse wave velocity (PWV) which define in our case as: PWV= L/x L is distance between the sensorsl and 2 as shows Fig.2 t is a time of the propagation pulse wave the distance L. How t is defined on the Fig.6 is shown.

In terms medical diagnoses PWV is a highly interesting subject.

Fig.7 illustrates simplified block diagram of the pulse width modulator that has the pulse duration of the which output voltage depends on the value of the capacitive Cs. This figure shows how a pulse width modulation signal is converted to digital code.

Modulators exist in many variations, but in general cases they produce pulse duration t, which one is defined by the formula: t = R*Cs'ln2 Where R is time drive resitor.

Fig. 8 shows a block diagram of all non-invasive pulse pressure and pulse wave velocity monitor. On the diagram capacitive sensors 1 and 2 are connected to the pulse width modulation 17 and 18, which produce a voltage pulse, duration of this pulse is proportional to capacitive sensors 1 and 2. In the result we have series pulses width modulation signal (PWMS). The law of modulation of the signal repeats the law of the change of capacitive sensors 1 and 2 respectively. Fig.7 shows more details how it happens. PWMS comes to inputs on the logic-gates 19 and 20. A high frequency signal comes to the other logical gate inputs, from the frequency synthesizer 16.

On the output of the logic-gates 19 and 20 signals are pulse width modulated and fill high frequency as show on Fig 7. These signals go to counters 21 and 22. These counters calculate the number of high frequency pulses, which are located in the limits by the pulse width modulation signals and then generate parallel codes on their outputs. From output of the counter 21 a code go to input of the decoder 23 and to microprocessor's module 6. From the output of the counter 22 the code comes to the input of the decoder 24. The decoders 23 and 24 on their output produce short pulse which equal the level of the pulse pressure wave as shown on Fig.7 and Fig.9. However, the pulse from 24 appear with delay from the initial one. The device 25 on its output produces pulse duration t, which is equal to the time it takes the blood pressure pulse wave travel from sensor 1 to sensor 2. The pulse is converted into a parallel code like PWMS and sent to microprocessor's module 6, where the microprocessor's module calculates blood pressure (systolic and diastolic), PWV and pulse rate according to a value L and software. The value L is sent to microprocessor's module 6 from module 8 by means of controller communication 28.

The microprocessor's module 6 include: 26 is the microprocessor, 27 is the additional memory, 28 is the controller communication with module 8.

The module 8 include: 29 is the controller communication with personal computer (f.e USB), is the keyboard with enables an operator to input various data (such as L), 31 is the controller communication with non-invasive blood pressure monitor.

Software (an algorithm of operation the noninvasive cuffless monitors) keeps in additional memory 27. The decoders 23, 24, the device 25 and microprocessor's module provide algorithm of operation with all the noninvasive monitors.

The algorithm of operation of this monitor is: Referring now to Fig.6 and Fig.9, which represent the plots of the blood pressure pulse waves (BPPW). On the amplitude of BPPW the part is highlighted between low level to high level like show on this figure. BPPW from sensor 2 delay compare to BPPW from sensor 1. As a result on the output of the decoder 22, there appear a short pulse (which relates to the high level) late on the interval of time x, then it happens on the output of the decoder 24. The situation is presented on the Fig.9 roughly, but more clearly. -4.

The device 25 generates voltage which is a long as x from two short voltage pulses (as show on Fig.9) which it converts in a parallel code and sends to microprocessor's module 6. This pulse must appeared once in a cardio cycle (see Fig.6). In order to reach this stage decoder 24 the signal "stop" sends to device 25 when pulse wave is higher then the high level.

The signal does not permit the device 25 to send a parallel code to 6. When amplitude of blood pressure waves for sensors 1 and 2 come down after maximum of these waves reach to low level, the decoder 23 a signal "start", sends to device 25. The signal allows 25 generate the pulse duration x and parallel cod according to it (see Fig. 9), when amplitudes of the blood pressure waves for sensor 1 and then 2 become equal to high level. This parallel code comes to microprocessor's module 6 from the site module acquisition of date 5. From site of the module 8 "set up" calibrates parameters and the value of distance between sensors L and input come into the memory 27 as well. Microprocessor uses these date and the software (which locates in 27) calculate systolic, diastolic, pulse wave velocity and pulse rate and show its on display 7. A power supply the monitors is a battery 32.

It will apparent to those skilled the in the design that the disclosed cuffless noninvasive monitor may be modified in numerous ways and may assume many embodiments other than the preferred forms specifically set out described above. Accordingly, it is intended by the appended claims to cover all such modifications of the invention within the true spirit and scope of the invention.

WHAT I CLAIM IS: 1 .A method of measuring blood pressure, pulse wave velocity and pulse rate compp^mg the steps of: a. passively measuring time of travel for each naturally occurring arterial mrise pressure wave between first and second locations separated sensors by^"predetermined distance; b. computing the systolic pressure, diastolic pressure, pulse rat^dnd pulse wave velocity for each naturally occurring pressure wave. 2. A blood pressure, pulse rate and pulse wave velocj^measurement system comprising: a. means coupled to a wrist radial artery^ first and second location for passively convicting each naturally occurring raf'iodical arterial pulse pressure wave into first and second changing of the elecjarcal parameters of sensors; b. means coupled to said converting means these parameters in a electrical modulation signal. c. means coupled to s^tf converting means for measuring time propagation pulse pressure wave froHfnrst to second sensors. d. means couplpcT to said converting means for computing the systolic pressure, diastolic pressure, pulse rate and pulse wave velocity for each pulse pressure wave. 3. Apdpacitive sensor comprising some membranes are fixed on the end thus dielectric spt(ce between membranes more space in center membranes then on the end. 4. A top membrane of the sensors has plate. By means of the plate sensors fix on strap. The size the plate more small then plates.

. A bottom membrane of the sensors has bulge. By means of the bulge reach better contact with wall of tho radial artery. — ■5- '2 may 2005 -2£ce/vg0

Claims (4)

i WHAT I CLAIM IS:

1. A cuffless portable monitor for continuous measurement of blood pressure, pulse rate and pulse wave velocity, the monitor comprises: a. two capacitive sensors, which are located at pre-determined distances. b. converter, which converts value of capacitive sensors into pulses width modulated signal and then into digital information.

2. A portable cuffless monitor claimed in claim 1, wherein the capacitive sensors, are made of a number of membranes, these membranes: a. are fixed on the two opposite edges. b. have such a surface curvature that the gap in the center is greater than on the edges. c. In order to enhance the parameters of the sensors, the shape of these membranes can be changed.

3. A portable cuffless monitor claimed in claim 1, wherein the bottom membrane of the sensors has a bulge, by means of which the capacitive sensor can get a better contact with the wall of the radial artery and as a result, becoming more sensitive.

4. A portable caffless monitor claimed in claim 1, wherein substantially as described and as illustrated accompanying drawings. IPONZ /1 AUG 4KB 6