Individual variation in the time course of symptoms during exercise in COPD

Breathlessness and leg fatigue are important symptoms during exercise in COPD patients. Breathlessness relates to increase in end-expiratory volume. Less is known about individual differences in the rate of change of symptoms with hyperinflation and whether this is influenced by the way data are presented and they relate to the severity of pre-exercise hyperinflation. We studied 15 stable COPD patients (11 male, mean (sd) age 65 (8) yrs, FEV1 0.91 (0.2) l, 32 (9)% predicted, IC 1.8 (0.4)l, 63 (13) % predicted) during constant load cycle ergometry at 70% VO2 max. We recorded intensity of breathlessness and leg fatigue on a Borg scale and IC every 2 minutes. We calculated the individual slopes of the change in these variables expressed as IC absolute and % predicted. There was a good relationship between symptoms and IC however expressed (r2 =0.25 p< 0.05). The individual slope of the dyspnoea/IC differed when %predicted changes were reported and values expressed in this way were not closely related to each other. There was a better relationship between the rate of change of dyspnoea and fatigue when expressed as absolute rather then % predicted (r2=0.74 p<0.01). Duration of exercise was not related to the IC% predicted before exercise the rate of change of breathlessness was greatest in patients with the highest baseline IC (r2 =0.5 p < 0.01). COPD patients show considerable variation in the rate at which symptoms develop during exercise, breathlessness relates to the degree of resting hyperinflation. Although fatigue scores show similar mean rates of change relative to IC the individual slopes are different to those for dyspnoea suggesting that different physiological processes underline these symptoms.