Prediction of peak oxygen consumption in obstructive airway disease

Abstract

The hypothesis of this study was that non-exercise variables can be used to reliably predict peak oxygen consumption (VO2) in patients with obstructive airway disease (OAD). We also evaluated the impact of symptoms on exercise capacity. Selected predictor variables included age, lung function, respiratory muscle strength, gas exchange, and the Baseline Dyspnea Index (BDI). In 40 patients peak VO2 was 19.9 +/- 8.7 (mean +/- SD) ml.kg-1.min-1 during progressive, incremental exercise until limited by symptoms on a cycle ergometer. Multiple regression analysis yielded three significant predictors: forced expiratory volume in one second (FEV1), age, and BDI. Peak VO2 (ml.kg-1.min-1) = 5.5 (FEV1) - 0.3 (age) + 0.8 (BDI) + 19.3 (R2 = 0.79; SEE: 4.2 ml.kg-1.min-1). Comparisons between patients who stopped exercise because of breathlessness (N = 14) and those who stopped because of leg fatigue (N = 18) showed that lung function, inspiratory muscle strength, and peak VO2 were significantly reduced in the former group compared to the latter. Peak exercise ventilation (VE)/MVV ratio was similar in the breathless (95.3 +/- 23.8%) and leg fatigue (86.8 +/- 20.3) groups, but peak heart rate (HR)/pred. HRmax ratio was significantly higher in the leg fatigue group (86.8 +/- 12.6%) than in the breathless group (75.1 +/- 8.6%) (P = 0.006). We conclude that lung function, age, and the clinical rating of breathlessness reliably predict peak VO2 in patients with symptomatic OAD. Moreover, peak exercise performance in OAD appears to be affected by different physiological factors which may be distinguished by the major symptom limiting exercise.