Patterns of fetal breathing in the baboon vary with EEG sleep state

Abstract

This report examines the hypothesis that the characteristics of breathing activity of the fetal baboon are modulated with respect to sleep state in a fashion similar to that observed in the human fetus. The pattern of fetal breathing activity was examined in relationship to electroencephalographic (EEG) sleep state in studies of six fetuses of chronically monitored pregnant baboons at 143–148 days of gestation (term, 175–180 days). Fetal breaths were defined by fluctuations of tracheal fluid pressure. EEG sleep states were defined with an automated method for discrimination of EEG patterns that are standard indices of quiet and active sleep in immature primates. During more than 250 h of recorded data, the fetuses spent on average 33.3 ± 3.9% of time in EEG quiet sleep. In comparisons across state the fetuses spent significantly ( P = 0.001) less time breathing during quiet than active sleep (49.5 ± 6.8 vs. 69.0 ± 3.8%). The inspiratory and expiratory time intervals of fetal breaths were not differentiated by EEG state but, the mean breath to breath interval was significantly ( P < 0.001) longer in EEG quiet sleep. In addition to these differences in incidence and time interval of breaths, during epochs of breathing, there was a significantly slower rate, lower amplitude, and lower variability of rate of breathing in quiet sleep (all P-values < 0.02). Thus, periodic breathing activity in the fetal baboon is present in both quiet and active EEG sleep states. Sleep states have a powerful influence on patterns of fetal breathing in the non-human primate, directly comparable to the human fetus.