Respiratory Muscle Function in Amyotrophic Lateral Sclerosis1–3

Respiratory muscle function was studied in relation to indices of lung function in a group of patients with amyotrophic lateral sclerosis. Mouth and transdiaphragmatic pressures during maximal static inspiratory and expiratory efforts were related to total lung capacity and its subdivisions, maximal expiratory flow-volume curves (with and without external resistive loads), lung resistance and compliance during quiet breathing, and arterial blood gases. Based on the shape of the maximal expiratory flow-volume curve, 2 groups were defined. In 12 patients (group 1) the maximal expiratory flow-volume curve appeared to taper normally as residual volume was approached. In 15 patients (group 2), flow decreased with concavity toward the volume axis, giving the impression that flow had dropped off the flow-limiting envelope as residual volume was approached. Group 2 patients, as compared to group 1 patients, had lower maximal static expiratory pressures (P < 0.05), higher residual volumes (P < 0.01), smaller vital...