Early heart rate response of normal human term fetuses to vibroacoustic stimulation.

Abstract

We examined cardiac reactivity in the first 45 seconds following a single 1 second vibroacoustic stimulus (VAS) to determine if the prestimulus fetal heart rate (FHR) pattern was predictive of the immediate post-VAS heart rate response. Forty-nine normal human fetuses between 37 and 41 weeks of gestation were observed to enter quiet sleep and remain in that state for 3 to 5 minutes before testing. In general, VAS elicited an initial acceleratory response of approximately 20 beats/min above the mean prestimulus heart rate followed by a deceleratory response to an average of approximately 4 beats/min below baseline values. Fetuses with different average prestimulus heart rate patterns generally differed in their early cardiac response to VAS: when compared to a high baseline FHR, a low resting heart rate was associated with a greater increase in heart rate above baseline (r = -0.401; P = 0.03), a greater decrease below prestimulus values (r = -0.312; P = 0.03), and a greater difference between maximum and minimum heart rates (r = -0.465; P = 0.001). Higher baseline heart rates were associated with lower FHR variability in the prestimulus period (r = -0.422; P = 0.009). When we examined the time course of the early response, we found that fetuses that achieved a maximum heart rate quickly exhibited less of an increase above prestimulus values (r = 0.894; P = 0.005), displayed a greater decrease below baseline (r = 0.507; P = 0.0002), and reached the minimum heart rate faster (r = 0.575; P = 0.0001) than fetuses that required longer to achieve a maximum cardiac response.(ABSTRACT TRUNCATED AT 250 WORDS)