Behavioral state affects heart rate response to low-intensity sound in human fetuses

The cardiac orienting reflex is elicited by a low-intensity sound, it consi sts of a sustained heart rate (HR) deceleration, and it is a specific physi ological correlate of cognitive processing. In this study we examined the r elationship between behavioral state and the cardiac orienting reflex in 75 human fetuses between 36 and 40 weeks gestation. Each fetus was stimulated with a 30-s speech sound at an average intensity of 83 dB SPL in quiet sle ep (QS) and active sleep (AS). The fetal cardiac electrical signal was capt ured transabdominally at a rate of 1024 Hz and fetal R-waves were extracted using adaptive signal processing. Fetal behavioral states were assigned ba sed on HR pattern and the presence or absence of eye and general body movem ents. We found that a significant HR deceleration occurred, in both QS and AS, following stimulus onset. However, HR decelerations occurred more often in QS than AS; and for fetuses exhibiting a HR deceleration, the magnitude of the deceleration was greater in AS compared to QS. In addition, in AS f emale fetuses exhibited a larger, more sustained HR deceleratory response t han male fetuses, but the seconds x gender interaction in QS was not signif icant. Based on these results, we concluded that behavioral state is an imp ortant determinant of the HR deceleratory response in human fetuses. (C) 19 99 Elsevier Science Ireland Ltd. All rights reserved.