The pulmonary vascular response to the sustained activation of the muscle metaboreflex in man

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 postexercise period. Nine healthy subjects performed isometric handgrip exercise at 50% of their maximal voluntary contraction force for 2 min. Exercise was followed by circulatory occlusion so as to maintain the muscle metaboreflex activated for 2 min (postexercise 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. Compared with baseline values, elevations in SPAP (by 20.06 +/- 2.08%), cardiac output (by 36.04 +/- 4.97%) and mean arterial pressure (MAP; by 25.62 +/- 3.54%) were noted during isometric exercise (means +/- 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 haemodynamic responses and intolerance of exercise.