We investigated the validity of transcranial Doppler recordings for the analysis of dynamic
responses of cerebral autoregulation. We found no significant differences in percentage
changes among maximal (centerline) blood flow velocity, cross-sectional mean blood flow
velocity, and signal power-estimated blood flow during 24-mm Hg stepwise changes in
arterial blood pressure. We investigated blood flow propagation delays in the cerebral
circulation with simultaneous Doppler recordings from the middle cerebral artery and the …

Aaslid and colleagues measured blood-flow velocity with transcranial Doppler in the middle
cerebral artery and in the straight sinus of human volunteers during acutely induced
hypotension. From these measurements, they determined the onset of autoregulatory
response in the cerebral circulation. They then compared their findings to earlier work my
colleagues and I published in which we studied the effect of acute hypotension on the
autoregulatory response of pial arterioles in anesthetized cats. Aaslid et al stated that the …