Arterial and microvascular contributions to cerebral cortical autoregulation in rats.

The responsiveness of the microvasculature and arteries during cerebral cortical autoregulation in rats was determined from measurements of microvascular pressures and blood flow as the systemic arterial pressure was altered. At systemic arterial pressures from 65 to 155 mmHg, cortical blood flow was essentially constant. Arterioles with a resting internal diameter of 20-70 microns responded by nearly equal proportional changes in diameter over this pressure range, but microvascular pressures were a linear function of arterial pressure. The percent of control changes in arterial and microvascular resistances at systemic pressures from 80 to 180 mmHg were nearly identical. Therefore, the microvasculature and arterial vasculature were approximately equally responsive to changes in arterial pressure over most of the autoregulatory pressure range. In addition, the arterial vasculature controlled 45-50% of the total vascular resistance at systemic arterial pressures from 40 to 180 mmHg. These data indicate that the cerebral vascular autoregulation in the rat depended substantially on the approximately equal responsiveness of the arterial vasculature and microvasculature. Similar results have been reported in cats and may indicate a common form of cerebral vascular control, which involves both the microvasculature and brain arteries among different species.