Investigation of cerebrovascular reactivity using transcranial Doppler sonography. Evaluation and comparison of different methods.

Cerebrovascular reactivity was investigated in 20 patients and 20 healthy subjects by Transcranial Doppler (TCD) sonography with four methods. Flow velocity at the middle cerebral artery (MCA) was recorded in the following conditions: a) rest; b) 60" hyperventilation; c) maximum voluntary apnea; d) air re-breathing in a closed circuit; e) 30' following the intravenous injection of 10 mg/kg acetazolamide. Circulatory and respiratory diseases influencing MCA velocity were exclusion factors. Flow velocity variations observed in the four experimental conditions (b-e) were transformed into % values of basal velocity; in the c) and d) tests the Reactivity Indices were computed, i.e. the ratios between velocity changes and PaCO2 increases. Each method proved effective in modifying MCA flow velocity, and produced typical patterns. Apnea, CO2 inhalation during air re-breathing and acetazolamide injection revealed impaired cerebrovascular reactivity in patients with multifocal ischemic lesions. A good correlation was observed comparing the apnea method to both CO2 inhalation and acetazolamide injection.