Effect of limb anesthesia on middle cerebral response to handgrip.

Transcranial Doppler ultrasound was used to measure middle cerebral arterial mean flow velocity (Vmean) on both sides of the brain in 12 subjects during hand contractions before and during regional anesthesia of the left arm. At rest Vmean was 49 (36-104) cm/s (median and range) and was unaffected by regional anesthesia. During right-hand contractions Vmean remained unchanged on the right side of the brain, whereas it increased 20 (4-37)% (P < 0.01) on the left side of the brain. Similarly, during left-hand contractions Vmean increased 24 (2-42)% (P < 0.01) on the right side of the brain, while it remained unchanged on the left side of the brain. Regional anesthesia did not quantitatively affect Vmean during right-hand contractions. In contrast, during left-hand contractions, both right and left Vmean tended to decrease. Increases in Vmean appeared despite a decrease in arterial carbon dioxide tension (P < 0.01). Heart rate and blood pressure responses to hand contractions were enhanced during regional anesthesia (P < 0.01), but left-hand contractions resulted in a less pronounced increase in blood pressure (P < 0.01). These data demonstrate a contralateral increase in cerebral perfusion during hand contractions that is dependent on intact afferent input from the working limb.