Lung function, maximum and submaximum exercise testing in COPD patients: Reproducibility over a long interval

Abstract

This study was designed to investigate the reproducibility and clinical relevance of several lung function and exercise test indices in a sample of patients with stable severe chronic obstructive pulmonary disease (COPD).

Twenty subjects (ages 67.8±2.0 years, forced expiratory volume in 1s, [FEV₁] 39.7±2.8% predicted) receiving conventional medical therapy and pulmonary rehabilitation were tested 4 times at 1 month intervals. Testing procedures included lung function (inspiratory vital capacity [IVC], FEV₁, plethysmographic functional residual capacity [FRC], specific conductance of the airways (sGaw), single breath transfer factor divided by the alveolar volume [T_L/VA]); incremental, progressive, symptom-limited, cycle exercise (maximum work load [$\dot V$ _max], maximum heart rate [HR_max], maximum ventilation [$\dot V$ _Emax], maximum oxygen uptake [$\dot V$ _O2max]); and 2 modes of submaximum exercise (12 min walking test [12 MWD] and endurance cycle test). The mean of the absolute value of the individual patient, session-to-session, variation was found to be 0.131 for FEV₁, 102 ml/min for$\dot V$ _O2max. The within-subject variability was the smallest for HR_max and IVC (mean intrasubject coefficient of variation, [$\overline {CV}$ intra] 5.0 and 6.5%) and the greatest for T_L/VA, the work performed during the endurance cycle test (EW) and sGaw ($\underline {VA}$ intra 16.5, 19.4, and 22.7%), while it was reasonably low (8.1–10.2%) for all the other variables studied. Calculation of the F ratio of the intersubject variance to the residual (total minus intersubject) variance, interpreted as a signal-to-noise ratio, yielded the following, in decreasing order: T_L/VA, EW,$\dot V$ _Emax,$\dot V$ _O2max, IVC, FEV₁, HR_max,$\dot V$ _max, sGaw, 12 MWD, FRC. If we assume that a useful variable should combine a low within-subject variability ($\overline {CV}$ intra ≤10%) with a high signal-to-noise ratio, we conclude that, among all the variables studied, IVC, FEV₁,$\dot V$ _Emax, and$\dot V$ _O2max are those with the greatest clinical potential for functional assessment in patients with COPD.