Cortical artery pressure in normotensive and hypertensive aneurysm patients

Cortical artery pressure (CAP) and systemic pressure (SP) were measured in eight normotensive and six hypertensive patients with anterior circulation aneurysms. In the hypertensive patients significant gradients developed between CAP and SP as these pressures were lowered. The relationship between CAP and SP was expressed by the best-fit equation CAP = 1.02 SP -9.27 in the normotensive patients and by CAP = 1.54 SP -65.60 in the hypertensive patients. In the latter, the cycle of decreasing and increasing pressures formed a hysteresis loop suggesting prolonged cortical vasoconstriction despite recovery of systemic pressure. Selective pressure measurements in the distal (D) and proximal (P) segments of the cortical arteries were also obtained. The D/P ratio describes the relative contribution of the collateral circulation to cortical artery pressure. In normotensive patients, the D/P ratio was maintained down to an SP of 48 mm Hg. In hypertensive patients this ratio decreased with lowered SP, and a critical closing pressure of 40 mm Hg was predicted for the distal circulation. These studies described the limited capacity of the cortical circulation to maintain perfusion pressure in hypertensive patients. These responses should be considered when assessing the risks associated with such procedures as carotid ligation or hypotensive anesthesia.