[Effect of corticosteroids on inspiratory muscle function]

Functional alteration in inspiratory muscles was evaluated in patients receiving corticosteroids for nonrespiratory diseases. Inspiratory muscle strength, as expressed by maximal inspiratory mouth pressure (PImax), and inspiratory muscle endurance (PmPeak/PImax), determined with a pressure threshold breathing device, were evaluated in 8 patients with normal pulmonary and inspiratory muscle function. There was a gradual decrease in both inspiratory muscle strength and endurance when corticosteroids were given. Tapered decrease in steroid dosage resulted in marked improvement in both strength and endurance, and the improvement was even more significant 6 months later. We also evaluated the ability of specific inspiratory muscle training to prevent the effects of therapeutic corticosteroids on inspiratory muscle function in 6 patients, as compared to 6 control patients who received sham training. Following corticosteroids there was a gradual decrease in both inspiratory muscle strength and endurance in those getting sham training. However, there was no significant change in inspiratory muscle function in those getting inspiratory muscle training. We conclude that corticosteroids result in significant deterioration in respiratory muscle function. This weakness is reversible by tapering steroid dosage, but can be prevented by specific inspiratory muscle training during corticosteroid treatment.