A method for retrieving the waveform of the pressure pulsations from the output of an electronic oscillometer

In the most common version of an oscillometric blood pressure monitor, the output from the pressure transducer, Y(t), is split into two parts, and used for separate determinations of the pressure inside the pneumatic cuff and its fluctuating part; the latter is derived by sending Y(t) to a high-pass filter (HPF) and amplifying the filtered part to obtain the oscillometric signal O(t). Using a typical HPF-amplifier combination, we show that if p(t), the pulsatile part of the cuff pressure, is defined to be a train of positive-going pulses, O(t) turns out to be rather close but not identical to dp/dt, and to demonstrate that one can easily retrieve p(t) from a record of O(t). This means that, with a small modification, the instrument can provide both p(t) and dp/dt; the practical advantages of this demonstration are pointed out.