2.2. Measurements

Baseline pulmonary function measurements of the participants were taken on a single day, which included postbronchodilator spirometry (CHESTAC-8800; Chest, Tokyo, Japan), residual volume (RV) measured using the closed-circuit helium method and diffusing capacity for carbon monoxide (DL_CO) assessed using the single-breath technique as reported by the American Thoracic Society and European Respiratory Society Task Force in 2005 [25]. Calculations of the predicted values for FEV₁ and vital capacity were carried out as recommended by the Japan Respiratory Society [26].