Air flow control apparatus and method for an automatic blood pressure gauge

摘要

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.