System and method for determining fetal heart rate

Claim 2

In a system for providing an output signal representative of the rate of a fetal heartbeat: means for receiving a Doppler signal which varies in frequency according to the rate of fetal heart movement, means for processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said predetermined range including at least one higher frequency which is harmonically related to a lower frequency in the range, means responsive to the processed Doppler signal for delivering output pulses at a rate corresponding to the fetal heartbeat, and means responsive to the output pulses for conditioning the means for delivering such pulses not to deliver pulses in response to harmonics of the Doppler signal whiCh may be present in the processed signal.

Claim 3

The system of claim 1 wherein the means for delivering output pulses includes a one-shot multivibrator adapted to switch to its unstable state in response to the processed Doppler signal and remain in said state for a period determined by a control signal from the means responsive to the output pulses.

Claim 4

The system of claim 2 wherein the means responsive to the output pulses provides a control signal for maintaining the multivibrator in its unstable state for a period on the order of 80 percent of the interval between successive ones of the output pulses.

Claim 5

The system of claim 2 wherein the multivibrator includes a timing circuit including a field effect transistor having a resistance determined by the control signal.

Claim 6

The system of claim 1 wherein the means for processing the Doppler signal includes a controlled gain amplifier for increasing the signal to a predetermined level, means for demodulating the amplified signal, and means for filtering the demodulated signal to eliminate frequencies higher than about 3.5 Hz.

Claim 7

In a method for determining the rate of a fetal heartbeat, the steps of monitoring a Doppler signal which varies in frequency at a rate corresponding to fetal heart movement, processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said range including higher frequencies which are related harmonically to lower frequencies in the range, delivering output pulses in response to the processed Doppler signal, and preventing the delivery of output pulses in response to harmonics of the Doppler signal, whereby the output pulses delivered provide an accurate indication of the fetal heart rate.

Claim 8

In a method for determining the rate of a fetal heartbeat, the steps of monitoring a Doppler signal which varies in frequency at a rate corresponding to fetal heart movement, processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said range including higher frequencies which are related harmonically to lower frequencies in the range, delivering output pulses in response to the processed Doppler signal, and preventing the delivery of output pulses in response to harmonics of the Doppler signal, whereby the output pulses delivered provide an accurate indication of the fetal heart rate.

Claim 9

The method of claim 6 wherein the delivery of output pulses in response to harmonics is prevented by the steps of monitoring the output pulses and preventing the delivery of such pulses for a period on the order of 80 per-cent of the interval between successive output pulses.

Claim 10

In a method for determining the rate of a fetal heartbeat, the steps of: receiving a Doppler signal which varies in frequency at a rate corresponding to the rate of fetal heart movement; processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeat, said range including higher frequencies which are harmonically related to lower frequencies in the range, switching a multivibrator from a first state to a second state in response to the processed Doppler signal to provide output pulses indicative of the fetal heart rate, monitoring the output pulses, and maintaining the multivibrator in its second state for a predetermined portion of the interval between successive output pulses to prevent the delivery of pulses in response to harmonics of the Doppler signal which may be present in the processed signal.

Claim 11

In a method for determining the rate of a fetal heartbeat, the steps of: receiving a Doppler signal which varies in frequency at a rate corresponding to the rate of fetal heart movement; processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeat, said range including higher frequencies which are harmonically related to lower frequencies in the range, switching a multivibrator from a first state to a second state in response to the processed Doppler signal to provide output pulses indicative of the fetal heart rate, monitoring the output pulses, and maintaining the multivibrator in its second state for a predetermined portion of the interval between successive output pulses to prevent the delivery of pulses in response to harmonics of the Doppler signal which may be present in the processed signal.

Claim 12

The method of claim 8 including the step of maintaining the multivibrator in its second state for a period on the order of 80 per cent of the interval between successive output pulses.

Claim 13

In a system for providing an output signal representative of the rate of a fetal heartbeat: means for receiving a Doppler signal which varies in frequency according to the rate of fetal heart movement, means for processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said predetermined range including at least one higher frequency which is harmonically related to a lower frequency in the range, variable width pulse generating means for delivering output pulses in response to the processed Doppler signal, the duration of the output pulses being determined by a control signal applied to the pulse generating means, means responsive to the output pulses for applying a control signal to the pulse generating means to condition said pulse generating meAns to deliver output pulses having a duration corresponding to a predetermined portion of the interval between successive ones of the output pulses, and means for selectively applying a reference control signal to the pulse generating means to establish an initial pulse duration and initiate operation of the system at a predetermined rate.

Claim 14

In a system for providing an output signal representative of the rate of a fetal heartbeat: means for receiving a Doppler signal which varies in frequency according to the rate of fetal heart movement, means for processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said predetermined range including at least one higher frequency which is harmonically related to a lower frequency in the range, variable width pulse generating means for delivering output pulses in response to the processed Doppler signal, the duration of the output pulses being determined by a control signal applied to the pulse generating means, means responsive to the output pulses for applying a control signal to the pulse generating means to condition said pulse generating meAns to deliver output pulses having a duration corresponding to a predetermined portion of the interval between successive ones of the output pulses, and means for selectively applying a reference control signal to the pulse generating means to establish an initial pulse duration and initiate operation of the system at a predetermined rate.

Claim 15

In a method for providing an output signal representative of the rate of a fetal heartbeat, the steps of: receiving a Doppler signal which varies in frequency according to the rate of fetal heart movement, processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said predetermined range including at least one higher frequency which is harmonically related to a lower frequency in the range, actuating variable width pulse generating means to deliver output pulses in response to the processed Doppler signal, the width of the output pulses being determined by a control signal applied to the pulse generating means, monitoring the output pulses, applying a control signal to the pulse generating means to condition said means to deliver output pulses having a width corresponding to a predetermined portion of the interval between successive ones of the output pulses, and selectively applying a reference control signal to the pulse generating means to establish an initial pulse width and initiate operation at a predetermined rate.

Claim 16

In a method for providing an output signal representative of the rate of a fetal heartbeat, the steps of: receiving a Doppler signal which varies in frequency according to the rate of fetal heart movement, processing the Doppler signal to eliminate frequencies outside a predetermined range corresponding to an expected range of fetal heartbeats, said predetermined range including at least one higher frequency which is harmonically related to a lower frequency in the range, actuating variable width pulse generating means to deliver output pulses in response to the processed Doppler signal, the width of the output pulses being determined by a control signal applied to the pulse generating means, monitoring the output pulses, applying a control signal to the pulse generating means to condition said means to deliver output pulses having a width corresponding to a predetermined portion of the interval between successive ones of the output pulses, and selectively applying a reference control signal to the pulse generating means to establish an initial pulse width and initiate operation at a predetermined rate.