Autoregulation ofcerebral blood flowduring controlled hypotension inbaboons

SYNOPSIS Theeffect ofgraded, progressive hypotensioni on theautoregulation ofcerebral blood flow was studied inanaesthetised baboons. Progressive hypotension was produced over a period of four tofive hours, either bygraded haemorrhage orbytheadministration ofincreasing concentrations ofhypotensive drugs. During haemorrhagic hypotension autoregulation was maintained until the mean arterial pressurehaddecreased to65%ofitsbaseline value, belowwhichcerebral bloodflow was pressurepassive. Inthoseanimals subjected todrug-induced hypotension, autoregulation persisted tolower levels ofmean arterial pressure(35-40% ofbaseline). Itispostulated that under conditions ofhaemorrhagic hypotension, constriction oftheextraparenchymal cerebral vessels in responsetosympathetic stimulation decreases thepossible rangeofautoregulation intheanaesthetised baboon.