Central origin of the hypoxic depression of breathing in the newborn.

These studies were designed to ascertain whether the mechanism underlying the depressive component of the response to hypoxia in the newborn is similar to that in the fetus. We studied the response to hypoxia in 5-10 day old unanaesthetized rabbit pups before and after decerebration at or near the level of the midbrain/pontine junction. In the intact animal, hypoxia caused an initial stimulation of minute volume (VE) followed by a depression which was due to a decrease in both tidal volume (VT) and respiratory frequency (f). Decerebration abolished the depressive component of the response; the initial increase in VE on exposure to 7% O2 was now maintained, mainly due to a sustained increase in VT. We conclude that there is a central mechanism sited in or above the upper pons which is involved in the depressive component of the biphasic response to hypoxia. It is likely that this mechanism is similar to that mediating the hypoxic depression of breathing in the fetus.