V62j autobox

Spirometry, whole‐body plethysmography, and single‐breath diffusion capacity for carbon monoxide were assessed using a pulmonary function testing system (Vmax Encore 229 with V62J Autobox; CareFusion, Yorba Linda, USA) according to standard procedures (Graham et al., 2019 (link); Macintyre et al., 2005 (link)). Pulmonary function measurements were expressed in absolute and percent predicted values (Crapo et al., 1982 (link); Quanjer et al., 2012 (link)). Blood hemoglobin concentration ([Hb]) was determined (HemoCue, Helsingborg, Sweden) to correct diffusion capacity measures. Measures of pulmonary function were performed in order to ensure that male and female participants were comparable.

Postbronchodilator (albuterol sulfate; ProAir HFA, Teva Respiratory, North Wales, PA) spirometry, body plethysmography [residual volume (RV), functional residual capacity (FRC), total lung capacity (TLC)], and diffusing capacity of the lung for carbon monoxide (D_LCO) measurements were performed (Vmax Encore with V62J Autobox, CareFusion, San Diego, CA) according to ATS/ERS guidelines (14 (link)–16 (link)). Maximum voluntary ventilation (MVV) was calculated as 40 times FEV₁ (15 (link)).

Participants reported to the laboratory on two separate occasions separated by at least 48 h. Participants were instructed to avoid caffeine for 8 h and exercise for 24 h prior to each testing session. Session 1 involved anthropometric measurements and pulmonary function tests (Vmax Encore 229 with V62J Autobox; CareFusion, CA, USA), which were performed in accordance with standard recommendations (Miller et al., 2005 (link); Wanger et al., 2005 (link)). Inspiratory muscle strength was measured using a semi‐occluded mouthpiece connected to a calibrated differential pressure transducer (DP15‐34; Validyne Engineering, CA, USA) as recommended (Laveneziana et al., 2019 (link)). Pulmonary function and inspiratory muscle strength results were presented in absolute units and as a percentage of predicted values (Black & Hyatt, 1969 (link); Gutierrez et al., 2004 (link); Tan et al., 2011 (link)). Participants were then familiarized with the scales used to record dyspnea during IPTL as well as the IPTL protocol itself. Session 2 was the primary testing session where participants engaged in IPTL until task failure. Diaphragm contractile function and voluntary activation were measured during session 2 only.