Chronic cerebral hypotension induces a downward shift of the cerebral autoregulation: a hypothesis based on TCD and OPG-GEE studies in ambulatory patients with occlusive cerebrovascular disease.

In order to establish whether or not the cerebral autoregulation is still effective at blood pressure rates in those who experience a chronic cerebral hypotension 37 patients were subjected to noninvasive CO2 enhanced transcranial Doppler (TCD) and ocular pneumoplethysmographic (OPG-GEE) studies of the middle cerebral and ophthalmic arteries. The patients demonstrating a combination of a unilateral patent internal carotid artery (ICA diameter reduction less than 49%) and a contra-lateral ICA occlusion based on duplex scan examinations were examined. The cerebral blood flow velocities at normocapnia (BFV) and pulsatility indices (PI) were measured by TCD. An equivalent of the reserve capacity of the cerebral autoregulation was estimated by quantification of the CO2 enhanced cerebral vasomotor reactivity (VMR). Cerebral blood pressure equivalents such as the OSP/BSP ratio and the ophthalmo-brachial systolic pressure (OBSP) index were estimated by measuring the ocular systolic blood pressure (OSP) and the systemic systolic blood pressure (BSP). The TCD and OPG-GEE data are both in the normal range distally to a patent ICA (n = 22). If the ICA is occluded the OPG-GEE data show a significant reduction in both OSP/BSP ratio's and OBSP indices. If the VMR was in the normal range, distally to an occluded ICA (n = 25), the pressure drop was mild and the BFV at rest was in the normal range. Nevertheless, the waveforms were more damped as seen from the reduction in pulsatility indices but the reduction did not reach statistical significance when compared to the PI values distally to a patent ICA.(ABSTRACT TRUNCATED AT 250 WORDS)