[Factors limiting exertion in respiratory diseases].

Factors limiting exercise capacity in patients with respiratory disease are determined in part by their response to an exercise test. Exercise tests evaluate the overall oxygen transport chain, i.e. exercise tolerance. The basic parameter is maximal oxygen consumption, VO2max which is very low in respiratory diseases. Decreased exercise tolerance results first from limited ventilatory capacity at maximal exercise: ventilatory reserve in these patients is low. At submaximal exercise, ventilation is on the contrary increased for a given exercise load. This relative hyperventilation is the consequence of the patient's general poor physical condition. In these patients the cardiovascular response to exercise is impaired because of decreased systolic ejection fraction related to bronchial obstruction. Finally, whatever investigation method is used, the metabolic response in patients with respiratory disease, i.e. peripheral muscle response, is greatly impaired. The aerobic is deficient and the anaerobic pathway predominates, sign that the sedentary status of these patients has altered their metabolic response.