Abstract: Method and apparatus for measuring airflow in a duct utilizing the technique of vortex shedding include inducing the shedding of vortices at a frequency within the range of sound, sensing the sounds generated by the shedding of vortices to determine the frequency of vortex shedding, and converting the frequency of vortex shedding into information indicative of airflow measurements.

Abstract: Disclosed herein is a circuit for automatically selecting between an ECG heartbeat signal source and a pressure/pulse signal source depending on which of the two sources is the most periodic between three successive heart beats. A pair of microprocessor internal timers commence a count-up cycle in response to a first detected heart beat from each of the two respective sources, after which count-down cycles are started in response to the next successive detected heart beats. The counting of the timers is then stopped in response to the third successive detected heart beats from the two sources and a comparison is provided to determine which of the two sources is most periodic, and should be used to trigger a heart rate monitor.

Abstract: Disclosed herein is a pacer signal reject circuit wherein an entire ECG waveform signal is applied to one input of an operational amplifier, while only the initial portion of the pacer signal including the main pulse and a portion of the tail, is applied to the second input of such operational amplifier, to cause cancellation of that initial portion from the ECG signal. Also, a synthesized version of the remainder of such pacer tail is generated and applied to the second input. Thus, by isolating the ECG signal from the second input except for a timed period of the pacer signal, and by applying the synthesized tail signal to such second input, the entire pacer signal may be cancelled.