Effect of acute hypoxia on metabolism and ventilation in awake piglets.

We studied the effect of acute sustained hypoxia on ventilation (VE) and oxygen consumption (VO2) over one hour during quiet wakefulness in young (6 days) and older (6 weeks) piglets in thermoneutral conditions during baseline, moderate hypoxia (PaO2 approximately 45 mmHg), and severe hypoxia (PaO2 approximately 30 mmHg). During severe hypoxia, ventilation and pH increased while PaCO2 decreased in both age groups. Blood gas changes (decreases PACO2, increases pH), but not ventilatory changes, were greater in the older piglets (P < 0.05). VO2 decreased similarly (-30%) while VE/VO2 rose over 160% in both age groups. During moderate hypoxia, changes in blood gas, VE, and VO2 were in a similar direction, but smaller in magnitude. We conclude that: (1) changes in blood gases and VO2 are amplified by maturation and severity of hypoxia and (2) blood gas changes are greater in older vs young piglets despite similar ventilatory responses suggesting maturational differences in CO2 production or dead space ventilation.