Vmax 22

Pulmonary function tests were performed according to the American Thoracic Society guidelines using Vmax 22 (Sensor Medics, Yorba Linda, CA, USA) and PFDX (Medgraphics, St. Paul, MN, USA) [17 (link)]. Post-bronchodilator FEV1 and FVC, total lung capacity (TLC), residual volume (RV), and Kco were measured at baseline and at each annual visit. Post-bronchodilator spirometry values were measured 15 min after administering 400 µg of salbutamol. Bronchodilator reversibility was defined as an increase in FEV1 that was 12% above the baseline value and at least 200 mL after administration [18 ]. Lung volumes, TLC and RV, were measured using body plethysmography with V6200 (CareFusion, San Diego, CA, USA), PFDX, or Vmax 22 [17 (link)]. Values for diffusing capacity (DLco) and predicted alveolar volume (VA) were measured by assessing the single-breath carbon monoxide uptake (Vmax 22 or PFDX). Measures of DLco were adjusted for hemoglobin concentrations using the equation provided by American Thoracic Society guidelines [19 (link)]. Kco values were calculated by dividing measures of hemoglobin-adjusted DLco (mmol/min/mmHg) by VA (L) [7 (link),20 (link)].

Spirometry was performed as recommended by the American Thoracic Society, using Vmax22 (SensorMedics, Yorba Linda, CA, USA). Absolute Values of FVC and FEV1 were obtained and the percentage of predicted values (% pred) for FEV1 and FVC were calculated from the following equations obtained in a representative Korean Population [15 (link)]. $\mathrm{Predicted}\mathrm{F}\mathrm{V}\mathrm{C}=4.8434–\left(0.00008633\times \mathrm{ag}{\mathrm{e}}^2\left[\mathrm{years}\right]\right)+\left(0.05292\times \mathrm{height}\left[\mathrm{cm}\right]\right)+\left(0.01095\times \mathrm{weight}\left[\mathrm{kg}\right]\right)$ $\mathrm{Predicted}\mathrm{F}\mathrm{E}\mathrm{V}1=3.4132–\left(0.0002484\times \mathrm{ag}{\mathrm{e}}^2\left[\mathrm{years}\right]\right)+\left(0.04578\times \mathrm{height}\left[\mathrm{cm}\right]\right)$
The highest FVC and FEV1 values of the tests with acceptable curves were used. Ventilatory patterns were defined as normal (FVC ≥80 % and FEV1/FVC ≥0.7), restrictive (FVC <80 % and FEV1/FVC ≥0.7; n = 45; 9.1 %), or obstructive (FEV1/FVC <0.7; n = 19; 3.8 %).
Subjects with normal patterns were subdivided into quartiles according to the baseline percentage of predicted values (% predicted) for FVC or FEV1. Based on the FVC, the resulting four categories were as follows: ≤99.3 % in quartile 1, 99.3–104.4 % in quartile 2, 104.4–112.7 % in quartile 3, and >112.7 % in quartile 4. Similarly, the subjects were also divided into quartiles based on the FEV1 values (% predicted): ≤97.9 % in quartile 1, 97.9–106.9 % in quartile 2, 106.9–118.2 % in quartile 3, and >118.2 % in quartile 4.

Spirometry was conducted according to American Thoracic Society guidelines (Vmax 22, SensorMedics; PFDX, MedGraphics) [17 (link),18 (link)]. The following values were evaluated: FVC, forced FEV1, the ratio of FEV1 to FVC (FEV1/FVC). All spirometric values were expressed as percentages of predicted values (percentage of predicted) [17 (link),18 (link)].