Apparatus and method for detecting a fetal heart rate

Abstract

An apparatus and method for detecting the heart rate of a fetus. The apparatus includes three detectors detecting heart beats of the fetus, each detector including at least two electrodes detecting ECG signals, the detectors being positioned on an abdomen of a mother in use. The apparatus also includes a processor coupled to the detectors, the processor being adapted to process the ECG signals received from the detectors and determine a heart rate of the fetus. The method of determining the heart rate of the fetus includes determining a position of the fetus within a womb, placing the detectors on an abdomen of the mother, monitoring the ECG signals obtained from the detectors for a predetermined length of time, and processing the ECG signals obtained from the detectors positioned on the abdomen of the mother to determine heart beats of the mother.

1 . An apparatus for detecting the heart rate of a fetus, the apparatus comprising:
 three detectors detecting heart beats of the fetus, each detector comprising at least two electrodes detecting ECG signals, the detectors being positioned on an abdomen of a mother in use; and   a processor coupled to the detectors, the processor being adapted to process the ECG signals received from the detectors and determine a heart rate of the fetus, wherein the processor includes
 means for detecting heart beats of the mother by determining when the ECG signals from the detectors positioned on the abdomen of the mother reach a maximum; and 
 means for determining the heart rate by determining a time interval between adjacent heart beats, so as to determine the heart rate of the mother, 
   wherein the processor is adapted to process signals from the detectors, one of whose electrodes are positioned such that one electrode lies beneath the umbilicus but above the symphysis pubis and the other is positioned at the uterus fundus.   
   
   
       2 . The apparatus according to  claim 1 , wherein the detectors include a common electrode, the electrodes of the detectors being adapted to be arranged in a kite shape. 
   
   
       3 . The apparatus according to  claim 1 , wherein the processor generates a weighted sum of the ECG signals detected by the detectors. 
   
   
       4 . The apparatus according to  claim 1 , the apparatus further comprising a signal processor amplifying and filtering the ECG signals detected by the detectors. 
   
   
       5 . The apparatus according to  claim 1 , the apparatus further comprising an output displaying an ECG trace of the heart beat of the fetus in accordance with the detected ECG signals. 
   
   
       6 . The apparatus according to  claim 1 , further comprising a filter filtering the ECG signals from the detectors so as to reduce noise. 
   
   
       7 . The apparatus according to  claim 6 , wherein the processor is adapted to correlate a maternal template with the filtered ECG signal to identify the temporal positions of maternal heart beats. 
   
   
       8 . The apparatus according to  claim 7 , wherein the processor is adapted to subtract the maternal template from the filtered ECG signal at the said temporal positions of the maternal heart beats to generate a fetal ECG exhibiting fetal heart beats but without exhibiting maternal heart beats. 
   
   
       9 . The apparatus according to  claim 8 , wherein the processor is adapted to correlate the fetal ECG in order to enhance the fetal heart beat portions of the fetal ECG. 
   
   
       10 . The apparatus according to  claim 8 , wherein the processor includes a bandpass filter filtering the fetal ECG to enhance the fetal heart beat portions of the fetal ECG. 
   
   
       11 . The apparatus according to  claim 10 , wherein the bandpass filter has a pass band of 25-40 Hz. 
   
   
       12 . The apparatus according to  claim 9 , wherein the processor is adapted to identify fetal heart beats by detecting maxima of the correlated fetal ECG. 
   
   
       13 . The apparatus according to  claim 10 , wherein the processor is adapted to identify fetal heart beats by detecting maxima of the filtered fetal ECG. 
   
   
       14 . The apparatus according to  claim 1 , wherein the processor is adapted to determine the heart rate of the fetus from the ECG signals by:
 suppressing portions of signal representative of the heart beat of the mother;   detecting heart beats of the fetus by determining when the remaining ECG signal reaches a maximum; and   determining the heart rate by determining the time interval between adjacent heart beats.   
   
   
       15 . The apparatus according to  claim 14 , wherein the processor is further adapted to perform the suppressing, detecting, and determining on the ECG signals detected by each detector and then aggregate the obtained heart rates over a predetermined time period of not less than one hour. 
   
   
       16 . The apparatus according to  claim 1 , wherein the apparatus is portable. 
   
   
       17 . The apparatus according to  claim 1 , wherein the processor is adapted to determine the standard deviation of each time interval between the heart beats detected, and to select the time intervals having a standard deviation lower than a predetermined value, so as to determine the heart rate in accordance with the time interval between adjacent heart beats. 
   
   
       18 . The apparatus according to  claim 17 , wherein the predetermined value is approximately 7 ms for four consecutive time intervals. 
   
   
       19 . The apparatus according to  claim 17 , wherein the processor is adapted to designate time intervals not selected, to be erroneous time intervals; and to modify the erroneous time intervals in accordance with the selected time intervals. 
   
   
       20 . The apparatus according to  claim 19 , wherein to modify the erroneous time intervals comprises comparing the erroneous time interval to the selected time intervals; determining the number of errors within the erroneous time interval; and dividing the erroneous time interval into a number of corrected time intervals by adding a number of heart beats corresponding to the number of errors to thereby subdivide the erroneous time interval. 
   
   
       21 . The apparatus according to  claim 20 , the processor being further adapted to average the time intervals and the corrected time intervals to determine a heart rate. 
   
   
       22 . A method of determining the heart rate of the fetus of using an apparatus having three detectors for detecting ECG signals representative of the heart beat of the fetus, the method comprising:
 determining a position of the fetus within a womb;   placing the detectors on an abdomen of the mother, the detectors being positioned in accordance with the position of the fetus;   monitoring the ECG signals obtained from the detectors for a predetermined length of time greater than one hour; and   processing the ECG signals obtained from the detectors positioned on the abdomen of the mother to determine heart beats of the mother by determining when the ECG signals reach a maximum, the heart rate of the mother from the time interval between maternal heart beats, and thereby the heart rate of the fetus,   wherein each detector has two electrodes, the electrodes of one detector being positioned such that one electrode lies beneath the umbilicus but above the symphysis pubis and the other is positioned at the uterus fundus.   
   
   
       23 . The method according to  claim 22 , wherein the detectors include a common electrode, the electrodes of the detectors being arranged in a kite shape. 
   
   
       24 . The method according to  claim 22 , wherein the predetermined length of time is greater than 12 hours. 
   
   
       25 . The method according to  claim 22 , wherein the determining the position of the fetus within the womb comprises palpating the mothers abdomen. 
   
   
       26 . The method according to  claim 22 , wherein the processing the ECG signals comprises:
 suppressing portions of the ECG signals representative of the heart beat of the mother;   detecting heart beats of the fetus by determining when the remaining ECG signals reach a maximum; and   determining the heart rate by determining the time interval between adjacent heart beats.   
   
   
       27 . The method according to  claim 26 , wherein the processing the ECG signals further comprises repeating the suppressing, detecting, and determining on the signals detected by each detector and then aggregating the obtained heart rates over a predetermined time period of not less than one hour. 
   
   
       28 . The method according to  claim 26 , wherein the suppressing portions of the ECG signal representative of the heart beat of the mother comprises:
 locating maternal ECG signals representing the heart beat of the mother; and   subtracting the maternal ECG signals from the ECG signals obtained from each detector.   
   
   
       29 . The method according to  claim 26 , wherein the determining the heart rate by determining the time interval between adjacent heart beats comprises:
 determining the standard deviation of each time interval for the heart beats detected during the predetermined time; and   selecting the time intervals having a standard deviation lower than a predetermined value.   
   
   
       30 . The method according to  claim 29 , wherein the predetermined value is approximately 7 ms for four consecutive time intervals. 
   
   
       31 . The method according to  claim 29 , wherein the method further comprises:
 designating time intervals not selected, to be erroneous time intervals; and   modifying the erroneous time intervals in accordance with the selected time intervals.   
   
   
       32 . The method according to  claim 31 , wherein the modifying the erroneous time intervals comprises:
 comparing the erroneous time interval to the selected time intervals; determining the number of errors within the erroneous time interval; and   dividing the erroneous time interval into a number of corrected time intervals by adding a number of heart beats corresponding to the number of errors to thereby subdivide the erroneous time interval.   
   
   
       33 . The method according to  claim 32 , the method further comprising averaging the time intervals and the corrected time intervals to determine a heart rate.