Impact of Transient Hypotension on Regional Cerebral Blood Flow in Humans

We examined the impact of progressive hypotension with and without hypocapnia on regional extracranial cerebral blood flow and intra-cranial velocities. Participants underwent progressive lower-body negative pressure until pre-syncope to inflict hypotension. End-tidal carbon dioxide was clamped at baseline levels (isocapnic trial) or uncontrolled (poikilocapnic trial). Middle and posterior cerebral artery blood velocities (transcranial Doppler), heart rate, blood pressure and end-tidal carbon dioxide were obtained continuously. Measurements of internal carotid artery and vertebral artery blood flow were also obtained. Overall, blood pressure was reduced by ~20% from baseline in both trials (P<0.001). In the isocapnic trial, end-tidal carbon dioxide was successfully clamped at baseline with hypotension, whereas in the poikilocapnic trial it was reduced by 11.1 mm Hg (P<0.001) with hypotension. The decline in the internal carotid artery blood-flow with hypotension was comparable between trials (-139 ± 82 ml; ~30%; P<0.0001); however, the decline in the vertebral artery blood flow was -28 ± 22 ml/min (~21%) greater in the poikilocapnic trial compared with the isocapnic trial (P=0.002). Regardless of trial, the blood flow reductions in internal carotid artery (-26 ± 14%) and vertebral artery (-27 ± 14%) were greater than the decline in middle cerebral artery (-21 ± 15%) and posterior middle cerebral artery velocities (-19 ± 10%),...
Source: Clinical Science - Category: Biomedical Science Authors: Source Type: research