AUTOREGULATORY VASODILATION OF PARENCHYMAL VESSELS IS IMPAIRED DURINGCEREBRAL VASOSPASM

Impaired CBF autoregulation during vasospasm after aneurysmal subarach noid hemorrhage (SAH) could reflect impaired capacity of distal vessel s to dilate in response to reduced local perfusion pressure or simply indicate that the perfusion pressure distal to large arteries in spasm is so low that vessels are already maximally dilated. Autoregulatory vasodilation can be detected in vivo as an increase in the parenchymal cerebral blood volume (CBV). Regional CBV, CBF, and oxy gen extractio n fraction in regions with and without angiographic vasospasm obtained from 29 positron emission tomography studies performed after intracra nial aneurysm rupture were compared with data from 19 normal volunteer s and five patients with carotid artery occlusion. Regional CBF was re duced compared to normal in regions from SAH patients with and without vasospasm as well as with ipsilateral carotid occlusion (P < .0001). Regional oxygen extraction fraction was higher during vasospasm and di stal to carotid occlusion than both normal and SAH without vasospasm ( P < .0001). Regional CBV was reduced compared to normal in regions wit h and without spasm, whereas it was increased ipsilateral to carotid o cclusion (P < .0001). These findings of reduced parenchymal CBV during vasospasm under similar conditions of tissue hypoxia that produce inc reased CBV in patients with carotid occlusion provide evidence that pa renchymal vessels distal to arteries with angiographic spasm after SAH do not show normal autoregulatory vasodilation.