Effects of hypocapnia on psychomotor and intellectual performance

Nine subjects performed five psychomotor tasks (two motor, two intellectual, and one combined motor and short-term memory) at three levels of PACO2 (38.5, 25.0 and 15.0 torr) with voluntary hyperventilation at 20 l/min. There were no performance decrements at PACO2 levels of 38.5 and 25.0 torr. At a PACO2 of 15.0 torr, there were no decrements of intellectual performance but there were highly significant decrements in motor performance. It is suggested that a lack of regional cerebral hypoxia, arising from compensating changes in regional cerebral blood flow, could be responsible for the preservation of intellectual performance at a PACO2 of 15 torr.