We have reported that 2-week-old piglets accumulate more lactic acid (LACT) upon repeated exposure to hypoxemia than 5-week old animals (Pediatr Res 35:325A, 1994). The animals were exposed to three 1-hour cycles of hypoxemia with a 1-hour recovery period in between. The aim of our study was to determine whether shorter, more rapid exposures to hypoxemia will influence the age-dependent response. 2-3 days after surgical implantation of EEG electrodes and vascular catheters (blood gases, LACT, pyruvate), six 2-week-old and seven 5-week-old piglets were studied in a metabolic chamber during quiet sleep. Alveolar ventilation was derived from PaCO2 and CO2 production. We exposed the animals to 5, 15-min cycle of hypoxemia(PaO2=30-35 mmHg) alternating with a 15-min recovery. There was a significant increase in LACT with the 1st hypoxemia exposure at both ages, the increase being much more marked at 5 than 2 weeks (393% vs. 122%, p < 0.01). Whereas each hypoxemia cycle brought an increase in LACT (p < 0.005) in the 5-week group, the magnitude of the change decreased with exposures. In the 2-week group, however, there was no significant change in LACT by the 4th exposure. The pyruvate levels increase in parrallel with those of LACT. There was no change in the ventilatory response to hypoxemia with the repeated exposures (average increase of ≅ 60% both in 2-week and 5-week groups). There was a small decrease in O2 consumption with hypoxemia for all exposures in the 5-week group only. In summary, whereas the 2-week old animals accumulate more LACT during prolonged hypoxemia, the 5-week group accumulate more LACT with the rapid short exposures. We conclude that both age and the pattern of exposure influence the metabolic response to moderately severe hypoxemia.
