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 (PaCO2) and lower arterial O2 tensions (PaO2) than adult sheep both at rest and during exercise. Nonetheless, the lambs maintained PaCO2 at or below the resting level throughout exercise. PaO2 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.