INFLUENCE OF POSTURE ON MIDDLE CEREBRAL-ARTERY MEAN FLOW VELOCITY IN HUMANS

We determined middle cerebral artery, common carotid artery and tempor al superficial artery Doppler derived flow velocities in ten subjects for 10 min after change in posture. Maximal changes were observed afte r about 3 min. The 10 degrees head-down tilt position increased blood velocities in the common carotid artery by 13% (SD 4)% (P < 0.001), in the middle cerebral artery by 6% (SD 3)% (P < 0.001) and in the super ficial temporal artery by 70% (SD 26)% (P < 0.001). In the standing po sition, there was an 18% (SD 9)% (P < 0.001) decrease in the common ca rotid blood velocities, with 14% (SD 6)% (P < 0.001) and 53% (SD 23)% (P < 0.001) reductions in the middle cerebral and superficial temporal artery velocities, respectively. At 9 min after the changes in postur e, velocities in the middle cerebral artery were at the value of supin e rest, whereas the common carotid blood velocity was not completely r estored and deviations in the temporal artery velocity persisted. The data would suggest that cerebral blood flow is regulated with some del ay and that such regulation is partially reflected in the common arter y blood flow, since changes in a branch of the external carotid artery flow velocity remained.