199 OXYGEN CONSUMPTION (VO2) AND TISSUE METABOLISM IN THE HYPOXIC LAMB

The observation has been made in the newborn (NB) animal that a fall in VO2 with alveolar hypoxia is not always accompanied by acidosis, suggesting that there is primarily a reduction in non-essential oxidative metabolism. To test this hypothesis we compared the metabolic consequences of an induced reduction in VO2 in conscious NB and older lambs. Seven lambs with chronic aortic and pulmonary arterial catheters were studied at < 7 days, at 1 mo. and at 2–3 mos. Sequential measurements were made at FIO2 = .21, .16, .12 and .08 obtaining: arterial and mixed venous blood gases, hemoglobin (Hb) concentrations, %HbO2, lactate (L), VO2, and CO2 production (VCO2). Base deficit (BD), cardiac output, systemic O2 transport (SOT) and R (VCO2/VO2) were calculated. All data were compared to measurements at FIO2 .21. In all groups when SOT fell sufficiently with hypoxia there was a fall in VO2. This occurred at a higher SOT in the NB (15 mlO2/min/kg) than lambs 2–3 mos (10 ml)2/min/kg). Δ L (L-L@control) consistently increased at all ages to ≥ 3 mMol/L whenever V)2 decreased to ≤ .7 × control VO2. Like L, BD and R increased significantly with a fall in VO2. Therefore we found that a comparable decrease in VO2 is attended by evidence of anaerobic metabolism at all ages; the major age related difference was the higher critical SOT at which this occurred in the newborn. Thus, the newborn does not seem to be less susceptible than the older subject to the impairment of oxidative metabolism caused by alveolar hypoxia.