The techniques of transcranial Doppler ultrasound and dynamic end-tidal forcing were used to study the dynamics of the middle cerebral artery peak flow velocity (V P) (i.e. index of cerebral blood flow) response to 60 min of sustained isocapnic hypoxia, isocapnic hyperoxia, euoxic hypocapnia, and euoxic hypercapnia in humans. Each protocol involved two 60-min interventions, with a 60-min recovery period between tests. Peak flow velocity increased significantly during hypoxia (14.7%) and decreased during hyperoxia (11.8%). During hypercapnia, VP increased significantly (33.6%) and remained elevated. There was no evidence of adaptation during these protocols. However, a significant adaptation was observed during hypocapnia. After an initial decrease (39%), VP increased significantly and stabilized at 25.2% below baseline. This adaptive component was found to be significantly faster during the second intervention. There were no significant differences between the first and second intervention for the remaining protocols.
Bibliography: p. 113-130
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