Circuit arrangement for producing a pulse sequence corresponding to a foetal cardiac rhythm

• US 3,916,878 A
• Filed: 05/29/1974
• Issued: 11/04/1975
• Est. Priority Date: 06/05/1973
• Status: Expired due to Term

• Current Assignee: Erich Courtin, Stefan Traub
• Original Assignee: Erich Courtin, Stefan Traub
• Inventors: Courtin, Erich, Traub, Stefan
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/474,474
• Time in Patent Office: 524 Days
• Field of Search: 128/2.5P,2.5R,2.5S,2.5T,2.6A,2.6F,2.6R
• US Class Current: 600/511
• CPC Class Codes: A61B 5/344 Foetal cardiography
• CPC Class Codes: A61B 5/4362 Assessing foetal parameters
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: H03K 5/156 Arrangements in which a continuous pulse train is transformed into a train having a desired pattern

Abstract

The present invention relates to a circuit arrangement for producing a pulse sequence corresponding to a foetal cardiac rhythm from a composite signal of an electrocardiogram which includes signals produced by the mother and other sources in addition to the desired foetal signals. The composite signal is conditioned to be within a predetermined dynamic amplitude range and applied to a noise filter. The noise filtered composite signal is applied to two signal processing channels which produce pulse sequences corresponding to the time interval between recurring maternal and foetal QRS complexes.

Claims

1. Circuitry for deriving a sequence of pulses corresponding to the heart rate of a foetus from a composite ECG signal which may include signals produced by the mother and other sources including electrical power line noise in addition to the desired foetal signals comprising:

means coupled to receive a composite ECG signal having repetitive foetal QRS complex signal component and a maternal QRS complex signal component, each having varying amplitudes and repetition periods for producing a composite output having dynamic amplitude variations within a predetermined dynamic range in response to the maternal QRS complex signal component of the composite ECG signal;

tracking band-rejection filter means connected to receive the composite output for suppressing electrical power lIne noise in the composite output and producing a noise filtered output in response to the composite output;

a first signal processing channel having a first band-pass filter connected to receive the noise filtered output of the tracking band-rejection filter means and having a pass range adapted to pass without appreciable attenuation frequencies of the maternal QRS complex signals which are lower in frequency than the frequencies contained in the foetal QRS complex signals and attenuate the amplitude of the foetal QRS complex signals and produce an output having foetal QRS complex signals of smaller amplitude than maternal QRS complex signals, first polarity-reversal means connected to receive the output of the first band-pass filter for ensuring that dominating components of the maternal QRS complex signals have a predetermined polarity and for producing an output having maternal QRS complex signals of said predetermined polarity, and a first trigger circuit connected to receive the output of the first polarity-reversal means for producing as an output a sequence of pulses in response to the appearance of the maternal signals;

a second signal processing channel having a second band-pass filter connected to receive the noise filtered output of the tracking band-rejection filter means and having a pass range adapted to pass without appreciable attenuation frequencies of the foetal QRS complex signals and attenuate frequencies of the maternal QRS complex signals for producing an output having maternal QRS complex signals attenuated in relation to the foetal QRS complex signals, a second polarity-reversal means connected to receive the output of the second band-pass filter for producing an output having the dominating component of each foetal QRS complex signal of a predetermined polarity, and a second trigger circuit connected to receive the output from the second polarity reversal means for producing as an output a sequence of foetal pulses in response to the foetal QRS complex signals;

interlock means coupled to the first trigger circuit and the second trigger circuit for producing interlocking pulses in response to the sequence of pulses produced by the first trigger circuit and for applying said interlocking pulses to the second trigger circuit during the occurrence of maternal QRS complex signals and for preventing the second trigger circuit from triggering during the occurrence of maternal QRS complex signals; and

error detector means connected to receive the output of the second trigger circuit for calculating an expectancy interval derived from at least one preceding foetal QRS complex signal period and for producing an error signal when no output is received from the second trigger circuit during the expectancy interval.

2. Circuitry as in claim 1 including:

means for producing a time-delayed indication of the foetal pulses produced in response to the foetal QRS complex signals, the time delay being at least the maximum physiological repetition period occurring between preceding successive foetal QRS complex signals; and

substituting means coupled to the error detector means for releasing a correction signal within the expectancy interval at a moment corresponding to the time interval between at least two preceding foetal pulses.

3. Circuitry as in claim 1 wherein the second trigger circuit comprises:

a peak rectifier having a main storage with a discharging time constant connected to receive the output from the second polarity reversal means and interlocking pulses from the interlock means for charging the main storage in response to the output from the second polarity-reversal means during an absence of an interlocking pulse output from the interlock means;

an auxiliary storage having the same discharging time constant as the main storage;

a first electronic switch coupled to the interlock means to receive the interlocking pulses and tO the second polarity-reversal means to receive the output from the second polarity-reversal means and connected to the main storage and the auxiliary storage for coupling the auxiliary storage to the main storage in response to receiving no output from the second polarity-reversal means and receiving no interlocking pulse and for uncoupling the auxiliary storage from the main storage in response to receiving either the output from the second polarity reversal means or an interlocking pulse; and

a second electronic switch connected to the interlock means to receive the interlocking pulses and to the main storage and the auxiliary storage for coupling the auxiliary storage to the main storage in response to receiving an interlocking pulse and for uncoupling the auxiliary storage from the main storage in response to not receiving an interlocking pulse.