VENTILATORY AND METABOLIC EFFECTS OF REPEATED HYPOXIA IN CONSCIOUS NEWBORN RABBITS

To estimate posthypoxia depressing effects on newborns, ventilatory an d metabolic effects of repeated hypoxia were studied in 1- to 3-day-ol d (group 1) and 2-wk-old (group 2) conscious rabbits. In group 1 (n = 18), ventilation was measured by means of a flow plethysmograph. The b arometric method was used in group 2 (n = 21). In an additional 19 of group 1 and 17 rabbits of group 2, oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured with an open-flow method. In control animals minute ventilation (VE), respiratory rate, tidal volum e, VO2, and VCO2 were recorded at 10-min intervals for similar to 100 min in room air. All variables did not change with time. Separate sets of newborns were exposed five times for 10 min to 10% O-2 in N-2. Eac h exposure was followed by 10 min of recovery in room air. VE measured during recoveries after hypoxia was returned to normal in group 1. In group 2, the normoxic VE during the last recovery was greater than th e first value in hypoxia-treated rabbits (P < 0.05) and greater than t he last value in control rabbits (P < 0.02). Although the VE response to hypoxia was not affected by repetitive exposures in group 2, at min ute 5 of the fifth exposure the VE response was greater than that duri ng the first trial in group 1 (P < 0.02). Although the VE response to hypoxia was not affected by repetitive exposures in group 2, at minute 5 of the fifth exposure the VE response was greater than that during the first trial in group 1 (P < 0.02). Repetitive exposures had no eff ects on metabolic response to hypoxia in all pups. Results of this stu dy indicate that hypoxia-related central inhibition, if developed duri ng the exposures, is reversed by 10 min of breathing room air in newbo rns. On the other hand, the increase in normoxic VE may suggest the pr esence of a long-lasting posthypoxia central excitation in rabbits dur ing the 2nd wk of life.