Automatic blood pressure measuring device

• US 4,917,116 A
• Filed: 09/22/1988
• Issued: 04/17/1990
• Est. Priority Date: 09/22/1988
• Status: Expired due to Fees

• Current Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Librett, Kevin S., La Viola, John
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/247,634
• Time in Patent Office: 572 Days
• Field of Search: 128/672, 128/677-686
• US Class Current: 600/494
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/0235 Valves specially adapted therefor

Abstract

A method and apparatus for determining mean blood pressure involves the use of a pre-programmed microprocessor which interprets pressure oscillation values from a pressure cuff affixed to a subject'"'"'s limb. The pressure cuff is inflated to a value above apparent systolic pressure and then deflated in steps. The steps are all substantially equal mmHg declinations in cuff pressure. At each step cuff oscillation values are taken and stored. The greatest cuff oscillation and its associated cuff pressure are noted, along with the next greatest cuff oscillations and associated cuff pressures on either side of the greatest oscillation. The actual means blood pressure is then determined by forming a window adjacent to the greatest oscillation and calculating, on which side of the greatest oscillation, within the window, the means pressure is disposed.

Claims

1. A method for determining a subject'"'"'s true mean arterial blood pressure, said method comprising the steps of:

(a) inflating a pressure cuff affixed to an appendage of the subject to a pressure which exceeds a predicted systolic blood pressure of the subject;

(b) deflating the pressure cuff in steps, while pausing between each deflation step;

(c) detecting, recording and storing cuff pressure oscillations at each pause between successive cuff pressure deflation steps;

(d) continuing the steps of deflating, detecting, recording and storing, until a cuff pressure is reached which is below the subject'"'"'s predicted diastolic blood pressure;

(e) identifying the maximum cuff pressure oscillation noted and a first cuff pressure associated therewith;

(f) identifying second and third next greatest cuff pressure oscillations on each side of said maximum oscillation, and second and third cuff pressures associated therewith; and

(g) using data from steps (e) and (f) and calculating the percentage difference between the second and third next greatest oscillations to calculate the true mean arterial blood pressure of the subject therefrom.

2. The method of claim 1 comprising the further step of using the data gathered from steps (e), (f) and (g) to calculate the oscillation in cuff pressure corresponding to the calculated true mean arterial blood pressure.

3. The method of claim 1 further comprising the step of identifying said first cuff pressure as the mean arterial blood pressure when said second and third next greatest oscillations are within about 15% of each other.

4. The method of claim 1 further comprising the step of indentifying the larger of said second and third next greatest oscillations as a target oscillation when the difference between the second and third next greatest oscillations is greater than 15%.

5. The method of claim 4 further comprising the step of identifying the cuff pressure corresponding to the target oscillation as the target cuff pressure.

6. The method of claim 5 further comprising the step of calculating one half of the difference between the target cuff pressure and the first cuff pressure and calculating true mean arterial blood pressure, Xmap by solving the equation:

space="preserve" listing-type="equation">X.sub.map =X.sub.m +/-dX.sub.w {1-[Y.sub.m (Y.sub.L -1)K]};

wherein;

X_m is the first cuff pressure;

dx_w is one half of the difference between the target cuff pressure and the first cuff pressure;

Y_m is the maximum cuff pressure oscillation;

Y_L is the target cuff pressure oscillation; and

K is an empirically derived constant.

7. The method of claim 6 further comprising the step of calculating the cuff pressure oscillation, Y_map which corresponds to X_map by solving the equation:

space="preserve" listing-type="equation">Y.sub.map =Y.sub.m (X.sub.map -X.sub.m) dY.sub.os /dX.sub.os ;

wherein;

dY_os is the difference between Y_map and the cuff pressure oscillation, Y_os which is the smaller of the second and third cuff pressure oscillations; and

dX_os is the difference between X_m and the cuff pressure, X_os corresponding to Y_os

8. A method for determining a subject'"'"'s true mean arterial blood pressure, said method comprising the steps of:

(a) inflating a pressure cuff affixed to an appendage of the subject to a pressure which exceeds a predicted systolic blood pressure of the subject;

(b) deflating the pressure cuff in steps, while pausing between each deflation step;

(c) detecting, recording and storing cuff pressure oscillations at each pause between successive cuff pressure deflation steps;

(d) continuing the steps of deflating, detecting, recording and storing, until a cuff pressure is reached which is below the subject'"'"'s predicted diastolic blood pressure;

(e) identifying the maximum cuff pressure oscillation noted and a first cuff pressure associated therewith,

(f) identifying second and third next greatest cuff pressure oscillations on each side of said maximum oscillation, and second and third cuff pressures associated therewith;

(g) identifying the first cuff pressure as mean arterial pressure when the second and third cuff pressure oscillations are within 15% of each other; and

(h) when the difference between the second and third cuff pressure oscillations is greater than 15%, calculating true mean arterial blood pressure, X_map by solving the equation;

space="preserve" listing-type="equation">X.sub.map =X.sub.m +/-dX.sub.w {1-[Y.sub.m (Y.sub.L -1)K]};

wherein;

X_m is the first cuff pressure;

dX_w is one half of the difference between the target cuff pressure and the first cuff pressure;

Y_m is the maximum cuff pressure oscillation;

Y_L is the target cuff pressure oscillation; and

K is an empirically derived constant.

9. The method of claim 8 further comprising the step of calculating the cuff pressure oscillation, Y_map which corresponds to X_map by solving the equation:

space="preserve" listing-type="equation">Y.sub.map =Y.sub.m (X.sub.map -X.sub.m) dY.sub.os /dX.sub.os;

wherein;

dY_os is the difference between Y_map and the cuff pressure oscillation, Y_os which is the smaller of the second and third cuff pressure oscillations; and

dX_os is the difference between X_m and the cuff pressure, X_os corresponding to Y_os.