Cerebral hemodynamics in Shy-Drager syndrome: variability of cerebral blood flow dysautoregulation and the compensatory role of chemical control in dysautoregulation.

Cerebrovascular autoregulation and CO2 reactivity were measured repeatedly in 3 patients with the multiple system atrophy type of autonomic insufficiency (Shy-Drager syndrome) by means of the 133Xe injection method. The degree of cerebral blood flow (CBF) dysautoregulation showed day-to-day variations in 2 of the 3 patients. The CO2 reactivity was normal or supernormal in the supine position in patients with impaired autoregulation. In the head-up position the response to CO2 was slightly suppressed in 2 of the patients, suggesting that chemical control may have tended to compensate for CBF dysautoregulation. It is concluded that the mechanism of chemical control of the cerebrovasculature is different from that which controls autoregulation and may have partially compensated for CBF dysautoregulation.