Microquark

Spirometry (microQuark, COSMED, Italy) was used to measure pulmonary function and maximal voluntary ventilation. The values of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and peak expiratory flow rate (PEFR) were used to indicate lung capacity, airway resistance, and gas exchange efficiency. Maximal voluntary ventilation (MVV) was collected by monitoring the maximal volume and effort of ventilation during an interval of 12 s. Each measurement was performed three times and averaged at each study time point to assure the measurement was reproducible and accurate.

All participants were tested for pulmonary function by an experienced clinical pathologist or nurse who had been especially in charge of pulmonary function tests at Hanyang University Hospital. The equipment used for lung function testing was a MicroQuark, which was manufactured by COSMED in 2013. For each test, calibration was carried out and the clinical pathologist performed three trials; the value of most reliable trial was coded. It was classified according to the GOLD criteria as an “obstructive pattern” when FEV1/FVC (%) was less than 70%, and “restrictive pattern” when FEV1/FVC (%) was more than 70% and FVC (%) was less than 80%.

Pulmonary function test was conducted using Microquark (COSMED, Roma, Italy) after entering sex, age, height, and weight of the participants. The pulmonary function test measured forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC), and maximum voluntary ventilation (MVV). In addition, Pony FX MIP/MEP (COSMED, Roma, Italy) was used to measure the changes in respiratory muscles. In a standing position, the participants positioned their legs shoulder width, holding the mouth piece with the mouth and nose closed with a clip. Maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) were measured in this position. After 3 light respirations, a total of 3 MIP and MEP were measured, and the highest values of each were used for analyzation. The measurement was performed 3 times by a skilled physiotherapists with many years of experience in pulmonary function test. Between each tests, 10-minute vreaks were given. Interrater reliability of pulmonary function test using Pony FX MIP/MEP is r = .99.^{[25 (link)]}

Spirometry (Cosmed Micro Quark, Cosmed, Italy) was performed on the same night as polysomnography. Measurements were repeated until maximal reproducible values of FEV₁ were achieved with variation of less than 150 ml between tests. The modified Medical Research Council dyspnoea scale (mMRC) was also recorded before polysomnography.