Received July 13, 2007
Revised August 17, 2007
Accepted after revision October 2, 2007

¹ University of Birmingham

^* To whom correspondence should be addressed. E-mail: g.m.balanos{at}bham.ac.uk.

	Abstract

The pulmonary circulation is influenced by the autonomic nervous system, yet whether this is physiologically important during exercise in man is not known. The aim of this study was to assess the pulmonary vascular response to sympathoexcitation induced by the maintained activation of the muscle metaboreflex in the post-exercise period. Nine healthy subjects performed isometric handgrip exercise at the 50% of their maximum voluntary contraction force for 2 minutes. Exercise was followed by circulatory occlusion so as to maintain the muscle metaboreflex activated for 2 minutes (post exercise circulatory occlusion; PECO). Blood pressure measurements and echocardiographically-determined estimates of systolic pulmonary artery pressure (SPAP) and cardiac output, were obtained at various intervals throughout the two protocols. Elevations in SPAP (20.06±2.08%), cardiac output (36.04±4.97%) and mean arterial pressure (MAP) (25.62±3.54%) were noted during isometric exercise as compared to baseline (mean ±S.E.M, All P<0.05). Increases in SPAP and MAP persisted during PECO (All P<0.05), whereas cardiac output returned to resting levels. Our findings suggest that the sympathoexcitation induced by isometric exercise affects the pulmonary circulation possibly by inducing vasoconstriction and/or stiffening the large conduit arteries. The exaggerated activation of the sympathetic nervous system that has been evidenced in cardiopulmonary patients could therefore be implicated in their abnormal pulmonary hemodynamic responses and intolerance of exercise.

Key Words: Isometric exercise, Pulmonary circulation, Sympathetic activity