FETAL HEART-RATE-VARIABILITY AND BEHAVIORAL STATE - ANALYSIS BY POWER SPECTRUM

OBJECTIVE: We attempted to determine the relationship between the fetal heart rate power spectrum and fetal state. STUDY DESIGN: Interbeat intervals, electrocortical activity, and fetal breathing movements were recorded from five near-term fetal lambs. Interbeat intervals were taken from epochs of low-voltage electrocortical activity with breathing, low-voltage electrocortical activity without breathing, and high-voltage electrocortical activity without breathing. Power spectral techniques were applied to determine the underlying frequencies contributing to fetal heart rate variability. Spectral analysis was also performed on fetal breathing data from three animals. RESULTS: Significant differences were found between low-voltage electrocortical activity with breathing and high-voltage electrocortical activity without breathing at 0.62 Hz and from 1.09 to 1.56 Hz. There was no clear relationship between the breathing and heart rate spectra. CONCLUSIONS: Fetal heart rate is mediated by both state and respiratory variables. The respiratory component is not strictly related to respiratory rate.