Apparatus and method for measuring blood pressure using linearly varying air pressure

• US 6,719,702 B2
• Filed: 05/28/2002
• Issued: 04/13/2004
• Est. Priority Date: 08/21/2001
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Jong-youn, Yoon, Gil-won
• Primary Examiner(s): Hindenburg, Max F.
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US10/155,136
• Publication Number:
  US 20030060720A1
• Time in Patent Office: 686 Days
• Field of Search: 600/481, 600/485, 600/490, 600/493, 600/494, 600/495, 600/496
• US Class Current: 600/490
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02225 using the oscillometric method

Abstract

An apparatus and method for measuring blood pressure using linearly varying air pressure, including a compression unit; an air pump that injects air into the compression unit; a pressure sensor that senses and outputs the air pressure of the compression unit; an ADC that converts and outputs the result of the sensing as a pressure signal; a controller that calculates a current pressure value of the compression unit from the pressure signal and a linear pressure of the compression unit that is linearly dropped corresponding to the current pressure value and generates the first control signal in response to the current pressure value and a second control signal from the result of a comparison of the current pressure value and the linear pressure; a DAC that converts and outputs the second control signal as an exhaust control signal; and a proportional control valve that exhausts air from the compression unit.

Claims

1. An apparatus for measuring blood pressure using linearly varying air pressure, comprising:

a compression unit to be applied to surround a predetermined site of an individual'"'"'s body, the compression unit being inflatable and deflatable;

an air pump that injects air into the compression unit in response to a first control signal;

a pressure sensor that senses the air pressure of the compression unit and outputs the result of the sensing;

an analog-to-digital converter (ADC) that converts the result of the sensing from an analog form into a digital form and outputs the result of the conversion as a pressure signal;

a controller that calculates a current pressure value of the compression unit from the pressure signal and a linear pressure of the compression unit that is linearly dropped corresponding to the calculated current pressure value, generates the first control signal in response to the current pressure value, and generates a second control signal from the result of a comparison of the current pressure value and the linear pressure to measure the blood pressure of the individual;

a digital-to-analog converter that converts the second control signal into an analog form and outputs the result of the conversion as an exhaust control signal; and

a proportional control valve that exhausts air from the compression unit in response to the exhaust control signal.

2. The apparatus as claimed in claim 1, wherein the predetermined site of the individual'"'"'s body is a finger.

3. The apparatus as claimed in claim 1, wherein the compression unit comprises:

an inlet tube through which air from the air pump enters the compression unit;

an outlet tube through which air is exhausted from the compression unit;

an air bag, which is inflatable or deflatable, is applied to surround the predetermined site of the individual'"'"'s body, and is connected to the inlet tube which takes in air and to the outlet tube which exhausts air,

wherein the time required for the air bag to reach a reference pressure value varies based on the circumference of the air bag changing according to the girth of the predetermined site.

4. The apparatus as claimed in claim 1, wherein the compression unit comprises:

a tube through which air from the air pump enters the compression unit or air is exhausted from the compression unit into the proportional control valve; and

an air bag which is inflatable or deflatable, is applied to surround the predetermined site of the individual'"'"'s body, and is connected to the inlet tube which takes in air and to the outlet tube which exhausts air,

wherein the time required for the air bag to reach a reference pressure value varies based on the circumference of the air bag changing according to the girth of the predetermined site.

5. The apparatus as claimed in claim 1, wherein the controller calculates the linear pressure P(i) using the formula below:

$P<br><br>\left(i\right)=P_{\max }-\frac{P_{\max }-P_{\min }}{f_s\times <br><br>t}\times <br><br>i$

where P_max and P_min denote the predetermined maximum and minimum pressures of the compression unit, respectively, f_s denotes a predetermined sampling frequency of the analog-to-digital converter, t denotes a period of time required until the maximum pressure P_max drops to the minimum pressure P_min, and i denotes the order of the pressure signal input from the analog-to-digital converter in the range of 0≦

i≦

f_s×

t.

6. The apparatus as claimed in claim 1, wherein the controller measures the time required for the compression unit to reach a predetermined pressure level using the pressure signal, and measures the blood pressure using the measured time and the current pressure value.

7. A method for measuring the blood pressure using linearly varying air pressure, comprising:

(a) injecting air into a compression unit until a reference pressure value is reached;

(b) calculating a current pressure value of the compression unit from a pressure signal output from an analog-to-digital converter (ADC), and a linear pressure for the current pressure value;

(c) determining whether the current pressure value is greater than the linear pressure;

(d) if the current pressure value is determined to be greater than the linear pressure, increasing a rate of dropping pressure of the compression unit;

(e) if the current pressure value is determined to be equal to or less than the linear pressure, decreasing the rate of dropping pressure of the compression unit;

(f) after (d) or (e), determining whether a number of current pressure values calculated is equal to f_s×

t, where f_s denotes a sampling frequency of the analog-to-digital converter and t denotes a period of time required until a maximum pressure P_max of the compression unit drops to a minimum pressure P_min;

(g) if the number of current pressure values is determined to be less than f_s×

t, then changing a variable i denoting the order of the pressure signal input from the analog-to-digital converter and proceeding to (b); and

(h) if the number of current pressure values is determined to be equal to f_s×

t, determining the blood pressure using the current pressure values in a quantity equal to f_s×

t.

8. The method as claimed in claim 7, wherein (a), injecting air into the compression unit, comprises:

(a1) injecting air into the compression unit;

(a2) sensing the air pressure of the compression unit;

(a3) converting a result of the sensing into a digital form to obtain a pressure signal;

(a4) determining whether the air pressure of the compression unit reaches the reference pressure value from the pressure signal and if the air pressure of the compression unit is determined not to reach the reference pressure value, proceeding to (a1); and

(a5) if the air pressure is determined to reach the reference pressure value, stopping the injection of air into the compression unit and proceeding to (b).

9. The method as claimed in claim 7, wherein (b), calculating the current pressure value and the linear pressure, comprises:

(b1) after (a), sensing the air pressure of the compression unit;

(b2) converting a result of the sensing into a digital form to obtain the pressure signal; and

(b3) calculating the current pressure value using the pressure signal and the linear pressure for the current pressure and proceeding to (c).

10. The method as claimed in claim 7, wherein if the linear pressure is calculated starting with i=0 in (b) and the number of current pressure values calculated is determined to be less than f_s×

t in (f), then the variable i is increased by 1 in (g), and the process proceeds to (b), and

if the linear pressure is calculated starting with i=f_s×

t in (b) and the number of current pressure values calculated is determined to be less than f_s×

t in (f), then the variable i is decreased by 1 in (g), and the process proceeds to (b).

11. The method as claimed in claim 7, wherein (h) comprises measuring the time required for the compression unit to reach a predetermined pressure level and determining the blood pressure using the measured time and the current pressure values.