Alterations of the Beneficial Effect of Deep Inspiration in Scleroderma: Relationships between Lung Function and Imaging

<i>Background:</i> It has been postulated that the beneficial effects of deep inspiration are dependent on the magnitude of airway distension by virtue of airway to parenchyma interdependence. <i>Objective:</i> This study was designed to examine whether the changes that occur in pulmonary fibrosis affect the beneficial effect of deep inspiration. <i>Methods:</i> Thirty-one subjects with scleroderma underwent lung volume and diffusion capacity assessment as well as high-resolution computed tomography. To assess the effect of deep inspiration, each subject underwent methacholine provocations in the absence of deep breaths. When the targeted change in lung function was achieved, subjects were asked to take 4 consecutive deep inspirations after which lung function measurements were repeated. The inspiratory vital capacity (IVC) was used as primary outcome. <i>Results:</i> Only 19 subjects attained the desired reduction in IVC in the absence of deep breaths. In those subjects, deep inspiration reversed the effect of methacholine on IVC by 48 ± 8.4%. The effect of deep inspiration correlated with DLCO% predicted (r = 0.55, p = 0.01), but not with high-resolution computed tomography abnormalities or baseline lung function measurements. When all subjects were considered, responsiveness to methacholine in the absence of deep inspiration was progressively lower with decreasing DLCO% predicted values (r = 0.51, p = 0.003). <i>Conclusions:</i> In systemic scleroderma, pulmonary abnormalities resulting in mild to moderate reduction in the diffusion capacity are associated with reduced ability of deep inspiration to reverse methacholine-induced early airway closure and bronchoconstriction. When diffusion capacity is severely affected, methacholine fails to produce obstructive airway changes.