Role of inspiratory capacity on exercise tolerance in COPD patients with and without tidal expiratory flow limitation at rest

Expiratory flow limitation promotes dynamic hyperinflation during exercise in chronic obstructive pulmonary disease (COPD) patients with a consequent reduction in inspiratory capacity (IC), limiting their exercise tolerance. Therefore, the exercise capacity of patients with tidal expiratory flow lim itation (FL) at rest should depend on the magnitude of IC, The presented st udy was designed to evaluate the role of FL on the relationship between res ting IC, other respiratory function variables and exercise performance in C OPD patients, Fifty-two patients were included in the study. Negative expiratory pressure (NEP) technique was employed to assess FL. Maximal work rate (WRmax) and o xygen uptake (V'O-2,max) were measured during an incremental symptom-limite d cycle exercise, Twenty-nine patients were FL at rest, The IC was normal in all non-FL patie nts, while in most FL subjects it was decreased. Both WRmax and V'O-2,max w ere lower in FL patients (p<0.001, each), A close relationship of WRmax and V'O-2,max to IC was found (r=0.73 and 0.75, respectively; p<0.0001, each). In the whole group, stepwise regression analysis selected IC and forced ex piratory volume in one second (FEV1)/forced vital capacity (FVC) (% predict ed) as the only significant contributors to exercise tolerance. Subgroup an alysis showed that IC was the sole predictor in FL patients, and FEV1/FVC i n non-FL patients. Detection of flow limitation pro,ides useful information on the factors tha t influence exercise capacity in chronic obstructive pulmonary disease pati ents. Accordingly; in patients with flow limitation, inspiratory capacity a ppears as the best predictor of exercise tolerance, reflecting the presence of dynamic hyperinflation.