CEREBRAL BLOOD-FLOW VELOCITY DURING AND AFTER SUSTAINED ISOMETRIC SKELETAL-MUSCLE CONTRACTIONS IN MAN

1. Twenty-seven young subjects used their right hand to perform sustai ned, isometric contractions at 40% of maximum for 2 min while lying su pine. 2. During the last 30 s of exercise, mean arterial blood pressur e increased by 38 +/- 4 mmHg (mean +/- S.E.M.) and heart rate by 27 +/ - 2 beats/min. 3. Nineteen of the subjects respired eucapnically durin g exercise, increasing ventilation by 4.1 +/- 0.5 litres/min. Eight su bjects hyperventilated (7.1-19.6 litres/min) and decreased end-tidal P CO2 by 8.2 to 15.1 mmHg during the last minute of exercise, 4. In the eucapnic subjects mean flow velocity in the right (i.e. contralateral to the activated cortex) middle cerebral artery increased by 11.4 +/- 1.0 cm/s, a change of 17%, during the contraction. This represents an increase in volume how to the territory of this vessel, but an increas e in global flow to the brain cannot be inferred. 5. In the eight subj ects who hyperventilated during exercise, there mas no rise of flow ve locity in the middle cerebral artery, and in some subjects there was a fail during the first 2 min of recovery, These findings suggest that if subjects hyperventilate during handgrip exercise there could be a f all in volume flow to many regions of the brain during and after the e xercise.