Effects of acute hypoxia on heat production capacity in newborn lambs.

Severe hypoxia during birth results in a metabolic acidosis and depressed heat production capacity. The aetiology of the depressed heat production capacity is unknown. To investigate this problem newborn lambs were exposed to a 30 minute period of hypoxia by causing them to breathe room air diluted with nitrogen. Heat production capacity was subsequently estimated as summit metabolic rate. When summit metabolic rate was estimated at the end of the period of hypoxia a depression to 66 per cent of the control value was observed (P less than 0.01) but no depression was observed when the estimation of summit metabolic rate was delayed for 30 minutes. Hypoxia resulted in metabolic acidosis, hyperlactaemia and considerable increases in the plasma concentrations of adrenaline and noradrenaline. Summit metabolic rate was positively correlated with blood pH at the beginning of summit metabolism in lambs which had a pH value of less than 7.05. There were no other relationships between summit metabolic rate and blood composition. These results suggest that the poor heat production capacity found in lambs which have suffered hypoxia during birth may be directly related to acidaemia.