Brachial artery diameter changes associated with cardiopulmonary baroreflex activation in humans.

Stimulation of receptors in the cardiopulmonary compartment produces a vasodilatation of forearm resistive vessels. A possible participation of large conduit arteries in such adjustments, studied in situ, has not been clearly documented in humans. We used a dual-crystal pulsed Doppler system to determine whether leg elevation in recumbent subjects is associated with changes in brachial artery diameter (BAD) and blood velocity (BV) in humans. BA diameter, velocity, and flow, together with arterial pressure and heart rate, were measured in 20 normal subjects in supine position and after passive leg raising. BAD increased immediately after leg elevation from 4.03 +/- 0.11 to 4.56 +/- 0.13 mm (P less than 0.001) parallel with an increase in BV from 6.05 +/- 1.18 to 7.1 +/- 1.36 cm/s (P less than 0.02). A positive correlation between BAD enlargement and BV increase was observed during the initial peak response (P less than 0.01). Subsequent measures indicated that BAD remained enlarged throughout the whole period of leg raising, whereas BV returned to the base-line values. Brachial artery volumic flow augmented during the initial phase of leg raising from 46 +/- 8 to 74 +/- 15.5 ml/min (P less than 0.01) and remained elevated throughout the whole period of leg elevation. This study shows that arteries participate in hemodynamic adjustments induced by positional changes associated with cardiopulmonary baroreflex activation.