Method and apparatus for calculating blood pressure with signal transformation

• US 20070049834A1
• Filed: 12/20/2005
• Published: 03/01/2007
• Est. Priority Date: 08/31/2005
• Status: Active Grant

• Current Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.)
• Original Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.)
• Inventors: Zhang, Xu, Ye, Jilun, Tao, Bo
• Granted Patent: US 7,594,893 B2
• Time in Patent Office: Days
• US Class Current: 600/494
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

A method and an apparatus for calculating blood pressure with signal transformation are provided, wherein said apparatus comprises: a pressure sensor, a pressure and pulse wave amplification circuit, an A/D converter, a microprocessor, a control circuit, an air bump and a valve component connected with the cuff gas circuit, a signal processing module and a ratio analysis module; and the method includes the steps of carrying out signal transformation of a time sequence of a sampled PW digital signal, calculating a maximum amplitude value and a corresponding frequency value based on the transformed signal, taking the maximum amplitude value as a amplitude value under the present pressure, carrying out continuously signal transformation of the time sequences of the PW digital signals at different pressure in order to constitute a PW amplitude-pressure curve and obtain an average pressure and a corresponding pulse rate from the PW amplitude-pressure curve, and finally calculating the systolic pressure and diastolic pressure with ratio method. With the method and apparatus according to the present invention, the measurement error can be reduced in case of the shiver, muscular fibrillation and the like of the human body being examined, and the measurement accuracy of blood pressure can be improved.

Claims

1. A method for calculating blood pressure with signal transformation, wherein the method includes steps of:

a. winding a cuff connected with a pressure sensor around an arm of a human body being examined, inflating the cuff to a certain pressure, and then deflating the cuff to a determined pressure;

b. maintaining the determined pressure for a predetermined time, continuously transforming both the pressure and a PW signal at the determined pressure into electric signals by the pressure sensor within the predetermined time, and transmitting the electric signals to an A/D converter circuit which converts the electric signals into a pressure value and a time sequence of a PW digital signal after the electric signals are amplified;

c. carrying out the signal transformation of the time sequence of the PW digital signal, calculating a maximum amplitude value and a frequency value corresponding to the maximum amplitude value at the determined pressure based on the transformed signal, taking the maximum amplitude value as an amplitude value at the determined pressure, taking the frequency value corresponding to the maximum amplitude value as a pulse rate value at the determined pressure, continuing to deflate the cuff to another determined pressure, and then returning to the step b till predetermined times;

d. constituting a PW amplitude value sequence and a pressure value sequence according to the amplitude value and the pressure value at each determined pressure, and then forming a PW amplitude-pressure curve according to the PW amplitude value sequence and the pressure value sequence;

e. calculating a mean pressure and a PW amplitude value P0 corresponding to the mean pressure based on the PW amplitude-pressure curve, respectively calculating PW amplitude values PS and PD which are corresponding to a systolic pressure and a diastolic pressure to be measured with ratio method, wherein PS=α

*P0, PD=β

*P0, α and

β

are a systolic pressure amplitude coefficient and a diastolic pressure amplitude coefficient respectively, and finally obtaining the systolic pressure and diastolic pressure based on the PW amplitude-pressure curve according to the PW amplitude values PS and PD.

2. The method for calculating blood pressure with signal transformation as claimed in claim 1, wherein the coefficients α

and β

in the step e are empirical coefficients obtained from experiments, the value of α

ranges from 0.2 to 0.9, and the value of β

ranges from 0.2 to 0.8.

3. The method for calculating blood pressure with signal transformation as claimed in claim 1, wherein the signal transformation of the time sequence the PW digital signal refers to Chirp-Z transformation of the time sequence of the PW digital signal.

4. The method for calculating blood pressure with signal transformation as claimed in claim 1, wherein the predetermined times range from 6 to 10 times, and the predetermined time ranges from 3 to 10 seconds.

5. The method for calculating blood pressure with signal transformation as claimed in claim 2, wherein the predetermined times range from 6 to 10 times, and the predetermined time ranges from 3 to 10 seconds.

6. The method for calculating blood pressure with signal transformation as claimed in claim 3, wherein the predetermined times range from 6 to 10 times, and the predetermined time ranges from 3 to 10 seconds.

7. The method for calculating blood pressure with signal transformation as claimed in claim 4, wherein for the PW amplitude value sequence and pressure value sequence obtained at different determined pressures in the step d, a normalization, interpolation and weighted average processing is performed, and the PW amplitude-pressure curve is constituted according to the processed PW amplitude value sequence and pressure value sequence.

8. The method for calculating blood pressure with signal transformation as claimed in claim 5, wherein for the PW amplitude value sequence and pressure value sequence obtained at different determined pressures in the step d, a normalization, interpolation and weighted average processing is performed, and the PW amplitude-pressure curve is constituted according to the processed PW amplitude value sequence and pressure value sequence.

9. The method for calculating blood pressure with signal transformation as claimed in claim 6, wherein for the PW amplitude value sequence and pressure value sequence obtained at different determined pressures in the step d, a normalization, interpolation and weighted average processing is performed, and the PW amplitude-pressure curve is constituted according to the processed PW amplitude value sequence and pressure value sequence.

10. An apparatus for calculating blood pressure with signal transformation, consisting of:

a data sampling unit including a cuff, a pressure sensor, a pressure amplification circuit, a PW amplification circuit and an A/D converter circuit, wherein the pressure sensor transforms a plurality of pressure and PW signals at different determined pressures into electric signals, which are transmitted to the A/D converter circuit and converted into pressure values and time sequences of PW digital signals after being amplified by the pressure amplification circuit and the PW amplification circuit respectively;

a primary control unit including a microprocessor with computer software and a control circuit, for controlling deflation time and deflation speed of the cuff according to the pressure signals and calculating blood pressure and pulse rate of a human body being examined by an arithmetic software;

an inflation and deflation unit including an air bump and a valve component which are connected with a cuff gas passage, for receiving control signals from the primary control unit to perform automatic inflation and deflation operation of the cuff, the apparatus further comprises;

a signal processing module, for performing signal transformation of the time sequences of the PW digital signals at a plurality of determined pressures outputted by the A/D converter circuit, to obtain amplitude-frequency characteristics of data being analyzed and then get maximum amplitude values at the different determined pressures, which are closely related with the blood pressure of the human body being examined;

a ratio analysis module, for extracting the amplitude values at the plurality of determined pressures outputted by the signal processing module and the pressure values at the plurality of determined pressures outputted by the A/D converter circuit, to obtain a PW amplitude value sequence and a pressure value sequence so as to form a PW amplitude-pressure curve, seeking a maximum amplitude value during the whole measure process from the PW amplitude-pressure curve, and finally calculating and outputting the blood pressure and pulse rate of the human body being examined according to a certain ratio.

11. The apparatus for calculating blood pressure with signal transformation as claimed in claim 10, wherein the signal transformation refers to Chirp-Z transformation of the time sequences of the PW digital signals.

12. The apparatus for calculating blood pressure with signal transformation as claimed in claim 10, wherein the ratio analysis module further comprises a normalization block, an interpolation block and a weighted average block, for carrying out a normalization, interpolation and weighted average processing of the PW amplitude value sequence and the pressure value sequence, and then constituting the PW amplitude-pressure curve according to the processed PW amplitude value sequence and pressure value sequence.

13. The apparatus for calculating blood pressure with signal transformation as claimed in claim 10, further comprising an auxiliary functional module bidirectionally connected with the microcomputer, for resetting system, detecting leakage and calibrating pressure.

14. The apparatus for calculating blood pressure with signal transformation as claimed in claim 11, further comprising an auxiliary functional module bidirectionally connected with the microcomputer, for resetting system, detecting leakage and calibrating pressure.

15. The apparatus for calculating blood pressure with signal transformation as claimed in claim 12, further comprising an auxiliary functional module bidirectionally connected with the microcomputer, for resetting system, detecting leakage and calibrating pressure.