Diaphragm function in patients with interstitial lung disease (ILD): a pilot study

Abstract

Abstract Diaphragm ultrasound (DUS) has been extensively used in critically ill patients receiving mechanical ventilation while data on its role in outpatients with interstitial lung disease is limited. The aim of this study was to describe the diaphragmatic function, as assessed by ultrasound, in outpatients with Connective Tissue Disease-associated ILD (CTD-ILD) and Idiopathic Pulmonary Fibrosis (IPF); in addition, we searched for relevant correlations between patients’ functional parameters and diaphragmatic function. Eighty-two subjects (41 CTD-ILD and 41 IPF) were prospectively enrolled while 15 healthy subjects served as controls. A portable ultrasound unit was used to measure, during quiet breathing, right diaphragm displacement (DD), right diaphragm inspiratory thickening (Ti), right expiratory thickening (Te), and right thickening fraction (TF) during follow-up visits. In patients with CTD-ILD, DD was lower compared with patients with IPF [1.4 (0.6–2.8) vs. 1.8 (0.9–2.6); p = 0.02] while (Ti) was significantly decreased in CTD-ILD patients compared with healthy subjects [0.17 (0.08–0.27) vs. 0.19 (0.12–0.24); p = 0.04]. Moreover, a positive correlation was observed between TF and all functional parameters assessed [FVC%pred. (r = 0.45, p = 0.003), TLC%pred. (r = 0.42, p = 0.006), FEV1 (L) (r = 0.39, p = 0.01) and DLCO% (r = 0.48, p = 0.001)]. Considering the entire population, a TF < 30% was associated with moderate dyspnea (mMRC ≥ 2) in multivariate analysis (OR 4.02, 95%CI [1.04–15.52]; p = 0.04). In conclusion, in patients with CTD-ILD diaphragmatic function is impaired. Specifically, diaphragm displacement and inspiratory thickening are significantly decreased in patients with CTD-ILD compared with IPF patients and healthy subjects. In the entire patient population, TF was an independent predictor of dyspnea and positively correlated with functional impairment.