DYSPNEA AND FLOW-VOLUME CURVE DURING EXERCISE IN COPD PATIENTS

The purpose of this study, in patients with chronic obstructive pulmon ary disease (COPD), was to examine the relationship of dyspnoea, rated on a visual analogue scale (VAS), to 1) tidal ventilatory variables m easured on exercise and 2) pre-exercise lung function. Twenty one pati ents (forced expiratory volume in one second (FEV(1)) mean (SD) 1.19 ( 0.32) l) were studied. During a preliminary test, the maximal workload was assessed and the upper end of the VAS was anchored. On the study day, the tidal now-volume curve on exercise was monitored and dyspnoea was assessed serially every minute. In each individual, the relations hip of dyspnoea to various tidal ventilatory variables was studied usi ng linear regression analysis; results were reported as squared correl ation coefficients, slopes and dyspnoea thresholds. Subsequently, the relationship of slopes and thresholds to pre-exercise lung function wa s examined. In all patients, dyspnoea showed a close correlation with ventilation, tidal volume, breathing frequency and tidal flow. The tid al peak inspiratory flow was the best individual predictor of dyspnoea with a median r(2) of 0.91. Patients with the poorest pre-exercise lu ng function exhibited the highest rates of increase in dyspnoea and th e lowest thresholds, the strongest correlation being observed between the dyspnoea/ventilation slope and pre-exercise maximal peak inspirato ry flow (r(2) = 0.54). In conclusion, for individual COPD patients dys pnoea on exercise is closely related to inspiratory flow. The degree o f pre-exercise ventilatory impairment accounts, at most, for only half of the variation in dyspnoea perception between subjects.