Changes in cerebral vasomotor reactivity to CO2 and autoregulation following experimental subarachnoid hemorrhage

Abstract Cerebral vasomotor capacitance to CO 2 and to autoregulation was measured before and after SAH. Carbon dioxide vasodilator capacitance was impaired shortly after SAH, but the vasoconstrictor response was not altered at this interval of time. Also impaired was the ability of autoregulation to compensate for a lack in perfusion pressure by vasodilatation shortly after SAH. One to 2 days after SAH, when cerebral edema and increased intracranial pressure were present, all types of vasomotor responses were impaired when CO 2 capacitance and autoregulation were evaluated. Explanation for these patterns of response related to changes in cerebral metabolism, vasomotor tone, and autonomic innervation during the early and later stages of SAH are discussed. Autoregulation was studied also before and after SAH. An autoregulation index was developed in order to compare the degree of impairment in the different groups of animals with various steady state values. During the early stage of SAH, impaired autoregulation was demonstrated only when CPP was reduced; however, after 24–48 hr, autoregulation was grossly impaired for increases and decreases in CPP.