Patent ID: 6245025
Filing Date: 2001-06-12
Classification: A61B

Abstract:
A method for measurement of fetal heart rate on the basis of acoustic signals originating from heat activity of a fetus and detectable on a maternal abdomen, the method comprising the steps of:measuring acoustic signals of fluctuating intensity originating from the heart activity of the fetus;converting said acoustic signals into electric signals;determining power levels (P.sub.a, P.sub.b) of said signals at a lower and at a higher test frequency (f.sub.a,f.sub.b), said lower and higher frequencies (f.sub.a,f.sub.b) being, respectively, in a lower and a higher frequency band of a frequency range of 20 to 80 Hz;detecting and storing local peak values (P.sub.a1, P.sub.a2 ; P.sub.b1, P.sub.b2) of said power levels (P.sub.a, P.sub.b) at different times (t.sub.a1, t.sub.a2 ; t.sub.b1, t.sub.b2) during an inspection period (t.sub.s) following the first one of said detected local peaks;counting numbers (n.sub.a, n.sub.b) of said peaks of power levels during said inspection period t.sub.s ;determining time differences between the times of detection of said peak values (P.sub.a1, P.sub.b1, P.sub.a2, P.sub.b2) within said inspection period (t.sub.s);identifying the detected peak as a said second sound, provided that said number (n.sub.a) of local peaks of said power level (P.sub.a) is one and said number (n.sub.b) of local peaks of said power level (P.sub.b) is one and said time difference (dt) between said peak values (P.sub.a2, P.sub.b2), is smaller than 15 ms;identifying the detected peak as a said first sound, provided that said number (n.sub.a) is one and for said time difference (dt) the criterion 15 ms<dt<40 ms is satisfied and for said power level (P.sub.b) measured at said time (t.sub.a1) corresponding of said peak values (P.sub.a1) of said power level (P.sub.a) the criterion (P.sub.b (t.sub.a1))/P.sub.b1 <0.3 is satisfied;identifying the detected peak as a said first sound provided that said number (n.sub.a) is one and said number (n.sub.b) is two and for said power level (P.sub.b) measured at the time (t.sub.a1) of said peak values (P.sub.a1) of said power level (P.sub.a) the criterion (P.sub.b (t.sub.a1))/P.sub.b1 <0.3 is satisfied;identifying the detected peak as a said first sound, provided that said number (n.sub.a) is two and said number (n.sub.b) is two;classifying a pair of identified peaks as heartbeat, provided that the measured time difference (t.sub.1,2) between the said first and second sound is in the range of 140 ms to 220 ms; andcalculating the fetal heart rate from the time difference between two consecutively identified heartbeats.