Reliability of the Determination of the Ventilatory Threshold in Patients with COPD

Purpose: The purpose of this study was to determine the interobserver reliability of the assessment of the ventilatory threshold (VT) using two methods in patients with chronic obstructive pulmonary disease (COPD) and in control subjects. Methods: VT was identified from incremental exercise testing graphs of 115 subjects (23 controls and 23 in each COPD Global initiative for chronic Obstructive Lung Disease class) by two human observers and a computer analysis using the V-slope method and the ventilatory equivalent method (VEM). Agreement between observers in identifying oxygen uptake at VT ((V) over dotO(2VT)) and HR at VT (HRVT) across disease severity groups was evaluated using intraclass correlation (for humans) and Passing-Bablok regression analysis (human vs computer). Results: For human observers, ICC (95% confidence interval) in determining (V) over dotO(2VT) were higher in controls (0.98 (0.97-0.99) both with V-slope and with VEM) than those in COPD patients (0.72 (0.60-0.81) with V-slope and 0.64 (0.50-0.74) with VEM). Passing-Bablok analysis showed that human and computerized determination of (V) over dotO(2VT) was interchangeable in controls but not in patients with COPD. Forced expiratory volume in one second and peak minute ventilation during exercise were the only variables independently associated with greater interobserver differences in (V) over dotO(2VT). Interobserver differences in HRVT ranged from 2 +/- 1 (controls) to 10 +/- 3 bpm (GOLD 4). Conclusions: In patients with COPD, the reliability of human estimation of (V) over dotO(2VT) is less than that in controls and not interchangeable with a computerized analysis. This should be taken into account when using VT for exercise prescription, as a tool to monitor responses to an intervention, as a surrogate measure of overall aerobic fitness, or as a prognostic marker in patients with COPD.