Exercise Tolerance in Chronic Airway Obstruction1, 2

Fifty men with chronic diffuse airway obstruction were studied to assess the extent to which symptom questionnaires, step-test responses, and lung function data predicted working capacity as measured in a progressive, unsteady state, exercise test on a cycle ergometer. Working capacity correlated significantly with grade of dyspnea, an observer's assessment of step-test responses, and with forced expiratory volume in one second and pulmonary diffusing capacity for carbon monoxide, but the prediction value of these indices was inadequate. To investigate how respiratory and circulatory adaptations were integrated with metabolism and to assess the factors limiting exercise tolerance, steady state exercise responses were studied at a work level corresponding to 60 per cent of working capacity. Effort tolerance was largely limited by a low ventilatory capacity. The cardiovascular response was essentially normal. Grouping patients according to previously reported criteria into type A (emphysema) and type B (chronic bronchitis) showed that total and alveolar ventilation was less in the type B than in the type A patients, but the cardiovascular responses were similar in the two groups. Working capacity in patients with a ventilatory limitation to effort is difficult to predict and needs to be measured directly; simple, standardized methods of testing exercise responses and increasing work loads enable intolerance to effort to be measured objectively.