Prognostic Value of a Diaphragmatic Endurance Test in Patients With Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease which involves respiratory muscles and can lead at short term to respiratory failure. The occurrence of respiratory failure is associated with morbidity and an increased mortality. To date, respiratory muscle weakness is predicted from the reduction of vital capacity, maximal inspiratory force, nocturnal symptoms and hypercapnia. Even taken together, the predictive value of these indices is low. The investigators hypothesize that an endurance test of diaphragmatic work would be more sensitive to respiratory muscle involvement than maximal respiratory force. Consequently, the investigators assessed diaphragmatic performance through an isocapnic hyperventilation test (IHT) in patients at the onset of ALS and, then regularly up to the occurrence of respiratory failure. The investigators make the hypothesis that IHT will be altered earlier than maximal inspiratory force