GB2114889A

GB2114889A - Blood pressure measurement

Info

Publication number: GB2114889A
Application number: GB08205328A
Authority: GB
Inventors: John Anthony Mcnulty
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-02-23
Filing date: 1982-02-23
Publication date: 1983-09-01

Abstract

Method and apparatus for measuring blood pressure using a first transducer 2 comprising a pick-up coil on a self adhesive mounting, which in use is attached to the patient's chest. A second transducer 4 is attached to the patient's wrist. The transducer 2 is connected to the input of a trigger circuit 6, so that when a voltage peak of a predetermined size appears in the pick-up coil 2, the trigger circuit produces an output pulse which is applied to the reset input of a counter 8. The output signal from the second transducer 4 is applied to a second trigger circuit 10, whose output is in turn applied to the "set" input of a bistable 12, whose "reset" line is connected to the output of the trigger circuit 6. A clock pulse generator 14 supplies clock pulses to the input of the counter 8, which are gated by the output from the bistable 12 by means of AND gate 16. The output from the counter 8 is supplied to the input of a calculator circuit 18, which is in turn connected to the input of a display 20. <IMAGE>

Description

SPECIFICATION Blood pressure measurement This invention relates to the measurement of blood pressure, and particularly to a "noninvasive" method of measuring blood pressure, that is to say, a method which does not involve the introduction of measuring devices into the patient's circulatory system.

The most common used non-invasive method of blood pressure measurement, is that in which an inflatable cuff is positioned around the limb of the subject, and air pressure is applied inside the cuff. However, this method is rather cumbersome in use, and the present invention seeks to provide a method of measuring blood pressure quickly and accurately without requiring the patient to be strapped into a special device every time a new measurement is required.

According to the present invention, there is provided a method of measuring blood pressure, comprising the steps of monitoring the electrical signal produced by the contraction of the main heart muscle, monitoring the consequent change of potential caused by the flow of blood reaching a remote monitoring point on the patient's body, and computing the blood pressure from a measurement of the time elapsed between the monitored signals.

Preferably, the remote monitoring point is at the extremity of a patient's limb, for example at the wrist, and the monitoring transducer may comprise a simple pick-up control which is adhesively attached to the patient's skin.

The invention also extends to apparatus for measuring blood pressure, the apparatus comprising a pair of monitoring transducers, adapted for attachment to the patient's body, trigger circuit means connected to one of the transducers, and arranged to start a timing device at the occurrence of a peak in an input waveform, and means for reading out the contents of the timer device, when a signal is received from the other transducer. Preferably, the apparatus also comprises means for calculating a blood pressure measurement, in accordance with the elapsed time measurement.

One embodiment of the invention will now be described by way of example, with reference to the accompanying drawing in which; Figure 1 is a circuit diagram of apparatus in accordance with the invention.

Figure 2 illustrates waveforms at different points in the circuit of Figure 1.

Referring to the drawing, a first transducer 2 comprises a pick-up coil on a self adhesive mounting, which in use is attached to the patient's chest. A second transducer 4 is attached to the patient's wrist. The transducer 2 is connected to the input of a trigger circuit 6, so that when a voltage peak of a predetermined size appears in the pick-up coil 2, the trigger circuit produces an output pulse which is applied to the reset input of a counter 8. The output signal from the second transducer 4 is applied to a second trigger circuit 10, whose output is in turn applied to the "set" input of a bistable 12, whose "reset" line is connected to the output of the trigger circuit 6. A clock pulse generator 14 supplies clock pulses to the input of the counter 8, which are gated by the output from the bistable 12 by means of AND gate 1 6.The output from the counter 8 is supplied to the input of a calculator circuit 18, which is in turn connected to the input of a display 20.

The operation of the circuit is as follows: when a positive going voltage peak is detected by the detector 2 at time T1 (as shown by waveform a in Figure 2) the trigger circuit 6 produces an output pulse (waveform b in Figure 2) which resets the counter 8 to zero, and also resets the bistable 12.

Since the output of bistable 12 is taken from the Q terminal, this results in a positive going pulse being applied to the input of AND gate 1 6, so that the clock pulses from pulse generator 14 are applied to the counter 8. Consequently, the counter begins to count up (waveform e of Figure 2) until the time T2 in Figure 2, when an input pulse is detected at the transducer 4, causing the bistable 12 to be set by the trigger circuit 10, so that the Q bar output goes negative. The output of counter 8 is supplied to a calculating circuit 18, which continuously computes the patient's blood pressure as a function of the elapsed time T. The output of the calculating circuit 18 is applied to a display 20 each time the counter is reset, by applying the output of 18 to a delay circuit 26, whose output is in turn applied to an AND gate 22.The AND gate 22 only applies its output to the display 20, when an enabling pulse is received at its other input, from a monostable 24 triggered by the 0 output of bistable 12. The delay circuit provides a delay of about 1 clock pulse, so that the output signal which corresponds to the maximum count in the counter (time T2 in Figure 2e) appears at one input of the AND gate 22, at the same time as the output pulse from monostable 24, since the leading edge of the latter pulse corresponds to the positive going output Q of the bistable 12.

This arrangement ensures that the display is updated at the completion of the measurement of each time interval.

In use, it would normally be necessary to "programme" the calculator circuit 18 with information relating to the patient's age, sex, weight etc to enable a meaningful measurement to be obtained, or the apparatus may be calibrated at an initial examination, using a conventional blood pressure measurement device, for example when the patient is first admitted for treatment.

Subsequently, the patient's condition can be monitored continuously without the necessity for using the normal manometric apparatus.

Instead of a special control circuit as described above, the invention may be used in conjunction with the electronic monitoring equipment commonly used for patients in intensive care situations, since in these situations an oscilloscope is frequently used to measure cardiac waveforms, and it is then only necessary to provide an additional input and a timing circuit to extract the elapsed time signal indicative of the patient's blood pressure.

Claims (Filed on 22/2/83).

1. A method of measuring blood pressure, comprising the steps of monitoring the electrical signal produced by the contraction of the main heart muscle, monitoring the consequent change of potential caused by the flow of blood reaching a remote monitoring point on the patient's body, and computing the blood pressure from a measurement of the time elapsed between the monitored signals.

2. A method according to claim 1 in which the remote monitoring point is at the extremity of one of the patient's limbs.

3. Apparatus for measuring blood pressure comprising a pair of monitoring transducers, adapted for attachment to the patient's body, trigger circuit means connected to one of the transducers, and arranged to start a timing device at the occurrence of a peak in an input waveform, and means for reading out the contents of the timer device, when a signal is received from the other transducer.

4. Apparatus according to claim 3 further comprising calculating means adapted to compute a blood pressure measurement in accordance with the said contents of the timer device.

5. Apparatus according to claim 4 comprising a pair of adhesive pick-up coils, a first trigger circuit connected to a first one of the said pick-up coils, and a second trigger circuit connected to the second of the said pick-up coils; a bistable circuit having its "reset" input connected to the first said trigger circuit and its "set" input connected to the second said trigger circuit; a counter having its "reset" input connected to the said first trigger circuit; a clock pulse generator arranged to supply clock pulses via gate means, to the said counter, the said gate means being connected to one of two outputs of the said bistable; and calculator means connected to the output of the said counter.

6. Apparatus according to claim 5 further comprising display means connected to the said calculator means and arranged to be reset to the other of said two outputs of the said bistable.

7. A method of measuring blood pressure substantially as herein described.

8. Apparatus for measuring blood pressure substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. waveforms, and it is then only necessary to provide an additional input and a timing circuit to extract the elapsed time signal indicative of the patient's blood pressure. Claims (Filed on 22/2/83).

7. A method of measuring blood pressure substantially as herein described.