Inflation of antishock trousers increases bronchial response to methacholine in healthy subjects

We studied changes in lung volumes and in bronchial response to methacholine chloride (MC) challenge when antishock trousers (AST) were inflated at venous occlusion pressure in healthy subjects in the standing posture, a maneuver known to shift blood toward lung vessels. On inflation of bladders isolated to lower limbs, lung volumes did not change but bronchial response to MC increased, as evidenced by a greater fall in the forced expiratory volume in 1 s (FEV1) at the highest dose of MC used compared with control without AST inflation (delta FEV1 = 0.94 +/- 0.40 vs. 0.66 +/- 0.46 liter, P less than 0.001). Full inflation of AST, i.e., lower limb and abdominal bladder inflated, significantly reduced vital capacity (P less than 0.001), functional residual capacity (P less than 0.01), and FEV1 (P less than 0.01) and enhanced the bronchial response to MC challenge compared with partial AST inflation (delta FEV1 = 1.28 +/- 0.47 liter, P less than 0.05). Because there was no significant reduction of lung volumes on partial AST inflation, the enhanced bronchial response to MC cannot be explained solely by changes in base-line lung volumes. An alternative explanation might be a congestion and/or edema of the airway wall on AST inflation. Therefore, to investigate further the mechanism of the increased bronchial response to MC, we pretreated the subjects with the inhaled alpha 1-adrenergic agonist methoxamine, which has both direct bronchoconstrictor and bronchial vasoconstrictor effects.(ABSTRACT TRUNCATED AT 250 WORDS)