Physiological and symptom determinants of exercise performance in patientswith chronic airway obstruction

To evaluate the physiological and symptom determinants of exercise performa nce (EP) as measured by a 6-min walking test (6MWD), Watt(max), and peak ox ygen consumption ((V over dot)O-2 ml/min/kg), 105 patients with chronic air way obstruction (CAO) [50 chronic obstructive pulmonary disease (COPD): 44 men, aged 63+/-7 years, forced expiratory volume in 1 sec (FEV1) forced vit al capacity (FVC)(-1)% 54+/-13, and 55 asthmatic: 23 men, aged 55+/-10 year s, FEV1 FVC-1% 65+/-10] underwent evaluation of 6MWD, symptom limited cyclo -ergometer exercise test, spirometry, respiratory muscle function. arterial blood gases and sensation of dyspnoea [using the Borg scale, Visual Analog ue Scale (VAS) and Baseline Dyspnoea Index (BDI)]. A hierarchical method of analysis identified the residual volume (RV), tota l lung capacity (TLC)(-1) ratio, BDI and the patient's age as the strongest and most consistent correlates of EP (r(2) = 0.14-0.21). The correlation b etween EP and its various determinants was not influenced by diagnosis. The relationship between breathlessness and EP was different between men and w omen: at any given level of exercise, women were more breathless than men. In multivariate analyses that contained both RV TLC-1 and BDI, the RV TLC-1 ratio was the strongest correlate of EP. although the BDI remained a signi ficant covariate. Overall, age was the major determinant of EP but inclusio n of the RV TLC-1 ratio and the BDI into the model explained a further 9-15 % of the variance in EP. These three covariates together explained 26-34% o f the variance between patients. We conclude that in stable CAO patients, the prediction of exercise capacit y by anthropometric, demographic, clinical and physiological variables is l ikely to be low. Age, pulmonary hyperinflation and dyspnoea are the stronge st and most consistent correlates of impaired exercise performance. Airways obstruction, measured during expiration using FEV1, does not appear to be a predictor of physiological impairment. These results underline the import ance of performing exercise evaluation in CAO patients.