Arterial blood gas tensions during exercise in neonatal lambs

At the onset of exercise, adult animals increase ventilation to match or exceed the metabolic requirement. This error-free regulation of arterial blood gas tensions may be attributable to 'adaptive feed-forward control' - respiratory control based on experience gained in infancy. This hypothesis predicts that neonates exhibit hypercapnia at the onset of exercise. To test this prediction, seven lambs were exercised on a treadmill at 0.8 m/sec at the ages of 2-5 days, and again at 9-12 days. Arterial blood samples were drawn pre-exercise and at 0.5, 1, 2, 5, 7 and 10 min of exercise. Seven adult sheep were similarly tested for comparison. The lambs had significantly higher arterial CO₂ tensions (Pa(CO₂)) and lower arterial O₂ tensions (Pa(O₂)) than adult sheep both at rest and during exercise. Nonetheless, the lambs maintained Pa(CO₂) at or below the resting level throughout exercise. Pa(O₂) rose significantly during exercise in the sheep and lambs. The results do not support the hypothesis since hypercapnia was not observed in the exercising neonatal lambs.