The sustained ventilatory response to hypoxic challenge in the awake newborn piglet with an intact upper airway.

The diphasic ventilatory response to steady-state hypoxia has been reported in anesthetised, intubated newborn piglets. We questioned whether this diphasic response persisted in the awake, spontaneously breathing piglet. Nine piglets, at one day of age, breathing spontaneously through a fitted mask and pneumotachograph were examined, monitoring the minute ventilation. (VE) tidal volume (VT), respiratory frequency (f), mean inspiratory flow (VT/TI), inspiratory time (TI). The piglets were studied in room air, followed by a step change to an FIO2 of 0.12, and a subsequent step-change to an FIO2 of 0.08. For each step-change in the FIO2 there was a decline in VT during hypoxia, but the VE increased significantly throughout the hypoxia through a progressive increase in both f and VT/VI. Thus, the awake newborn piglets were able to sustain the increase in VE during hypoxia. These results differ from previous observations of the diphasic VE response to hypoxia in lightly anesthetised piglets suggesting that the ventilatory response to steady state hypoxia is dependent upon experimental conditions. Further, the finding of a sustained ventilatory response in awake piglets breathing through an intact upper airway differs from previous studies in lambs and kittens suggesting a difference in the level of maturity at birth between the species.