Oscillometric blood pressure monitor employing non-uniform pressure decrementing steps

• US 5,052,397 A
• Filed: 12/04/1986
• Issued: 10/01/1991
• Est. Priority Date: 07/05/1985
• Status: Expired due to Fees

• Current Assignee: Critikon Co. LLC
• Original Assignee: Critikon, Inc.
• Inventors: Medero, Richard, Hood, Rush W. Jr., Ramsey, Maynard III
• Primary Examiner(s): SHAY, DAVID M
• Application Number:
  US06/937,946
• Time in Patent Office: 1,762 Days
• Field of Search: 328/672, 328/677-682, 328/685
• US Class Current: 600/495
• CPC Class Codes: A61B 5/02116 of pulse wave amplitude A61B5/02225 takes precedence
• 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

Abstract

The deflation of the inflatable and deflatable cuff worn by a subject during automatic sphygmomanometric measurement is accomplished in unequal size decrements and principally in larger steps than 7 Torr. Each step after detection of the initial oscillations is determined in the first instance by reference to a look-up table or an equation as a function of prevailing cuff pressure. This Base Step dimension is augmented by a factor proportional to the last oscillation amplitude, the factor being increased after detection of the maximum oscillation amplitude. A valve mechanism with at least two different effective orifice sizes is used for deflation, the smaller size effective orifice being used first, to maintain control over the decrement step rate while holding the time for decrement within a predetermined limit of 8 mSec. per Torr, i.e., maintaining the rate above 125 Torr per second. The valve mechanism can consist of two valves with unequal orifice size, or it can consist of two equal orifice size valves to be used singly for providing the effective smaller orifice, or in parallel to provide the effective larger origice. Alternatively a single variable orifice valve can be used.

Claims

1. Automated sphygomomanometric apparatus comprising in combination:

(a) an inflatable and deflatable pressure cuff;

(b) inflating means operatively coupled to said cuff for selectively supplying a gaseous medium under pressure to said cuff to inflate and pressurize said cuff;

(c) cuff pressure sensing means coupled to said cuff for sensing cuff pressure including any oscillations therein;

(d) deflate valve means coupled to said cuff for selectably releasing said gaseous medium from said cuff in successive decrements; and

(e) control means interconnecting said inflating means and said deflate valve means with said cuff pressure sensing means for inflating and deflating said cuff while performing a blood pressure measurement on a subject;

characterized in that said deflate valve means comprises means for providing at least two different pressure dependent flow rates, one faster and one slower for any given cuff pressure, for releasing said gaseous medium from said cuff, and said control means comprises means for initiating release of said gaseous medium from said cuff using said deflate valve means that provides the slower flow rate and continuing to use said slower-flow-rate-providing deflate valve means until the deflation rate has slowed to a predetermined value whereupon said control means uses said faster-flow-rate-providing deflate valve means; and

further characterized in that said pressure decrementing steps are determined, at least in part, so as to satisfy the equation;

space="preserve" listing-type="equation">Decrementing Step=k.sub.1 +k.sub.2 (CP)

where "CP"=cuff pressure and "k₁ " and "k₂ " are constants having respective values on the order of 4 and 0.05.