The collateral hemispheric systolic pressure.

Satisfactory calibrated BP tracings were obtained during 385 (85%) of 455 carotid endarterectomies. The pressures were measured from the distal common carotid arteries while the external carotid arteries were clamp occluded. Continuous recordings were made with and without proximal common carotid clamp occlusion. The two systolic pressures resulting in each patient were plotted as a single point on a graph, with the direct carotid systolic pressure on the abscissa and the back carotid systolic pressure on the ordinate. Formulae of the mean values in 101 of the 385 procedures, in which the opposite carotid systems contained severe stenoses or total occlusions, and the other 284 procedures, in which the opposite carotid systems had no notable lesions, demonstrate that the collateral hemispheric systolic pressure depends on the status of the opposite carotid artery and on the central BP. We derived formulae for these two groups of patients to demarcate the lowest collateral hemispheric systolic pressure adequate for hemispheric integrity during and following prolonged operative carotid occlusion or following permanent interruption of carotid blood flow as a result of thrombosis, ligation, or resection without graft replacement.