Overall Contribution of Chest Wall Hyperinflation to Breathlessness in Asthma

Abstract

Studies suggest that the increased volume of both abdominal and rib cage compartments of the chest wall contribute to dyspnea during methacholine-induced airway narrowing. Eight male patients with asthma aged 34 +/- 13 years (mean +/- SD) before and during methacholine challenge. The volume of the chest wall (Vcw), volume of the abdomen (Vab), and volume of the rib cage (Vrc) were measured by using a three-dimensional optoelectronic plethysmography. During methacholine challenge, the increase in end-expiratory Vcw (Vcw,ee) [0.55 +/- 0.23 L, p < 0.001] was due to increased Vrc (0.37 +/- 0.20 L, p < 0.01) and, to a lesser extent, Vab (0.18 +/- 0.10 L, p < 0.005). Linear univariate regression analysis showed that changes in dyspnea (Borg scale) with the highest methacholine dose correlated with both DeltaFEV(1) and DeltaVcw,ee. Multiple regression analysis with the Borg score as dependent variable and all other ventilatory indexes as independent variables showed that DeltaVcw,ee and DeltaFEV(1) were the only significant contributors to the Borg score. Taken together Vcw,ee and FEV(1) explained 56% of variance in the Borg score (r(2) = 0.56), although Vcw,ee explained 48% of it. During methacholine challenge in patients with asthma, the overall increase in Vcw,ee is a better predictor of dyspnea that the reduction in FEV(1).