Siemens Medical Electronics, Inc.

James M Chickering

Scott W Newell

Andres Aguirre

An automatic blood pressure gauge generates a signal representing the instantaneous pressure levels in a blood pressure cuff. This pressure signal includes a slowly changing component representing a deflating cuff and a more rapidly changing component representing blood pressure pulses that are mechanically coupled to the cuff. The pressure signal is DC coupled to a microprocessor. The microprocessor filters the pressure signal using a minimum order-statistic filter coupled in cascade with a median order-statistic filter to generate an auxiliary signal having peaks at the starting points of the pulses. This auxiliary signal is used to generate a signal representing the slowly changing component of the pressure signal. The slowly changing component of the pressure signal is subtracted from the pressure signal, leaving only the blood pressure pulse signal. The microprocessor then generates a function representing peaks of the blood pressure pulses versus a corresponding cuff pressure at which they occur. From this function, the microprocessor calculates mean, systolic and diastolic pressures using extrapolation and/or interpolation.

Pulse signal extraction apparatus for an automatic blood pressure gauge

A deflation control system for the pressurized cuff of an automatic blood pressure gauge uses a pressure sensor to control solenoid valves. The solenoid valves are responsive to respective pulse signals having variable duty cycles to change their time-apertures and, thus, their flow rates. The duty cycles of the pulse signals are controlled to maintain a desired constant rate of pressure reduction in the cuff. A microprocessor generates a control value which determines the duty cycles of the pulse signals. This value is proportional to the initial volume of fluid in the cuff and to a predictive term which is provided from a table that is indexed by cuff pressure. This value is then augmented by a feedback term, generated by a feedback control loop to ensure an accurate deflation rate. The gain of the feedback loop is selected so that the feedback correction signals do not interfere with pulse signals modulating the pressure signal. The feedback term is normalized by the initial volume measurement. In addition, any new valve setting is applied in small steps over a time interval to further ensure smooth changes in the flow rate.

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Newton, NH, United States of America

James M Chickering