Fetal heart rate monitoring apparatus

Claim 1

In apparatus for monitoring heart beat activity in which means are provided for obtaining electrical Doppler signals from ultrasonic Doppler shifted information derived from heartbeat motion, the arrangement comprising: filter means for passing a first band of frequencies including selectively actuable means for passing a second band of frequencies in lieu of the first band, of said electrical Doppler signals; tunable resonant circuit means for de-emphasizing in the passed band of frequencies, frequency content other than that closely about the resonant circuit frequency for providing an output signal indicative of fetal heart rate; phase detector means responsive to a phase shift between input signals to and output signals from the resonant circuit means, for tuning the resonant circuit means at a preselected rate in accordance with the detected phase shift; timing means defining a first pulse period in response to said input signals and defining a second pulse period in lieu of the first, for inhibiting the response of said phase detector means during the pulse period defined; and rate detector means operatively coupled to the output signal indicative of fetal heart rate for separately controlling said filter means and said timing means in response to respective preselected different values of the heart rate signal.