The effect of feeding on cerebral blood flow and oxygen consumption in the new-born calf.

1. The effect of feeding on cerebral blood flow and oxygen consumption has been investigated in unrestrained calves between 7 and 28 days after birth.2. Cerebral blood flow was determined using an inert gas clearance technique, and oxygen consumption by the simultaneous measurement of the arterio-cerebral venous oxygen content difference.3. Cerebral blood flow increased during feeding from 74 +/- 4 to 116 +/- 9 ml. 100 g(-1) min(-1) and reverted afterwards to the pre-feed level. No alteration in cerebral oxygen consumption occurred.4. Feeding was associated with an increase in mean arterial blood pressure and heart rate, and mild asphyxia.5. The sensitivity of the cerebral circulation to alterations in arterial P(CO2) was investigated in seven calves under sodium pentobarbitone anaesthesia. In the range of arterial P(CO2) 15-75 mm Hg the relationship was linear (r = 0.71; P < 0.001) with an average slope of 0.68 ml. 100 g(-1) min(-1) mmHg P(a,CO2) (-1).6. Increases in mean arterial blood pressure comparable to those occurring during feeding (96 +/- 6 to 159 +/- 8 mmHg) were produced by compression of the thoracic aorta in three calves under sodium pentobarbitone anaesthesia and were associated with an increase in cerebral blood flow from 48 +/- 4 to 76 +/- 8 ml. 100 g(-1) min(-1). No significant change in calculated cerebral vascular resistance occurred during either feeding or aortic compression.7. These results suggest that the rise in blood pressure which occurs during feeding in the calf exceeds the autoregulatory capacity of the cerebral circulation.