Stem pressure at the origin of intracranial collateral vessels

The relationship between pressure at the functional site of origin of intracranial collateral channels (Pstem) and systemic pressure allows an estimation of the size of vascular channels from which collateral vessels originate. In this study, Pstem was determined in anesthetized dogs. A branch of the middle cerebral artery was perfused through a closed system with autologous blood. Tissues with regional cerebral blood flow (rCBF) less than or equal to 10 ml.100 g-1.min-1 (collateral-dependent zone) were identified using radioactive microspheres. Sequential injections of nonradioactive microspheres were made into the cannulated vessel to progressively occlude the terminal capillary bed. Injection of nonlabeled spheres was terminated when backpressure no longer increased, and the final rCBF measurement was made. There was a linear relationship between backpressure and flow to the collateral-dependent tissues. When rCBF within these tissues was zero, the corresponding value for backpressure (Pstem) was 79 +/- 4% (mean +/- SD) of mean arterial pressure. The high value for Pstem suggests that cerebral collateral channels arise in part from large vessels.