Peak flow and peak cough flow in the evaluation of expiratory muscle weakness and bulbar impairment in patients with neuromuscular disease.

Objective: To study the expiratory muscle force and the ability to cough estimated by the peak expiratory flow and peak cough flow in patients with Duchenne muscular dystrophy and amyotrophic lateral sclerosis.

Design: A total of 27 patients with amyotrophic lateral sclerosis and 52 patients with Duchenne muscular dystrophy were studied. From the group of 144 normal subjects of this laboratory, we selected 38 for comparison.

Results: The maximal inspiratory pressure in patients with Duchenne muscular dystrophy and amyotrophic lateral sclerosis was 64.5 +/- 24.7% and 37.8 +/- 21.8%, respectively, and maximal expiratory pressure was 64.2 +/- 32.5% and 37.7 +/- 21.6%, respectively. Patient groups showed a significant lower peak expiratory flow than normal subjects. Higher peak cough flow than peak expiratory flow was found in all groups. The peak cough flow-peak expiratory flow difference was 46 +/- 18% in normal subjects, 43 +/- 23% in patients with Duchenne muscular dystrophy, and 11 +/- 17% in patients with amyotrophic lateral sclerosis. The peak expiratory flow and peak cough flow were not different in bulbar onset amyotrophic lateral sclerosis. In patient groups, the dynamic and static behavior correlated positively.

Conclusions: These results suggest that peak cough flow-peak expiratory flow is useful to monitor expiratory muscle weakness and bulbar involvement and to assess its evolution in these patients.