Journal of Applied Physiology, Vol 77, Issue 2 902-911, Copyright © 1994 by American Physiological Society
Hyperbaric oxygenation increases arousal and breathing movements in fetal lambs
M. H. Tiktinsky-Rupp, S. U. Hasan, B. Bishop and F. C. Morin 3rd
Department of Physiology, State University of New York at Buffalo 14214.
Oxygenation produced by distending the lungs with 100% O2 increases the
occurrence of arousal and fetal breathing movements (FBM), particularly
during non-rapid-eye-movement (NREM) sleep, in fetal sheep of > or = 135
days of gestation. We studied the breathing and behavioral responses to a
rise in arterial PO2 (PaO2) without lung distension in fetuses between 128
and 132 days of gestation. Twelve fetuses were chronically instrumented to
record FBM, behavioral state, blood pressure, arterial blood gas tensions,
and pH. Fetal PaO2 was raised by having the ewe breathe 100% O2 at 3
atmosphere absolute pressure spontaneously (group 1, n = 5, 129 +/- 1 days
of gestation) or with mechanical ventilation to control fetal arterial PCO2
(group 2, n = 7, 131 +/- 1 days of gestation). Hyperbaric oxygenation
raised fetal PaO2 by 20 Torr in both groups. During hyperbaric oxygenation,
the occurrence of arousal increased severalfold in both groups. The
occurrence of FBM increased during arousal in both groups, during
rapid-eye-movement sleep in group 1, and during NREM sleep in group 2. The
timing of diaphragmatic activity during arousal and the variability of
diaphragmatic activity during NREM sleep were different than those in
rapid-eye-movement sleep. We conclude that oxygenation without lung
distension increases the occurrence of arousal and of FBM, principally
during arousal and NREM sleep, in fetuses of < or = 135 days of
gestation.
