The effect of arterial PCO2-variations on ocular and cerebral blood flow in the newborn piglet.

The response of ocular and cerebral blood flow to different arterial PCO2 levels was studied in ventilated paralyzed newborn piglets with the radionuclide-labeled microsphere method. The retina and the choroid have different blood flow responses to variations in arterial PCO2 levels. Retinal blood flow (ml/g/min) was increased during hypercarbia, from 0.26 +/- 0.03 at baseline to 0.51 +/- 0.07 (PaCO2 8.7 +/- 0.2 kPa) and 0.62 +/- 0.07 (PaCO2 11.0 +/- 0.2 kPa). However, no significant change was found in choroidal blood flow during hypercarbia. Cerebral blood flow was more responsive to PaCO2 than retinal blood flow, increasing from 0.71 +/- 0.03 at baseline to 2.25 +/- 0.25 (PaCO2 8.7 +/- 0.2) and 1.77 +/- 0.13 (PaCO2 11.0 +/- 0.2). Hypocarbia did not influence either retinal or choroidal blood flow.