RESPONSE OF MIDDLE CEREBRAL-ARTERY VOLUME FLOW TO ORTHOSTASIS

Fifteen healthy subjects were tilted at 70-degrees from the horizontal during a period of 4 min while recording the Doppler signal from the middle cerebral artery. Digital signal analysis carried out off-line provided the following data: mean spatial velocity (vBAR), signal power (pBAR) as an index of cross-sectional area, (vBAR.pBAR) as an index of volume flow. Flow as averaged over the entire period of tilted position was found to be 101 +/- 25% of the supine steady state. There was evidence for autoregulatory vasodilation including the trunk of the middle cerebral artery. In a patient suffering from orthostatic dysregulation flow fell to 49% of its value as measured in supine position. From the evidence of this observation the clinical application of the method seems to warrant further study.