In a previous study performed by us, functional alterations in the inspiratory muscles were evaluated in patients receiving
corticosteroids for diseases other than respiratory. We have shown that patients who received high-dose
steroids for several weeks developed inspiratory
muscle weakness that was reversible following withdrawal of the
drug treatment. The present study was designed to evaluate the ability of specific inspiratory muscle training (SIMT) to prevent the effects of a therapeutic dosage of
corticosteroids on inspiratory muscle function in patients receiving the
drug for diseases other than pulmonary, with no underlying respiratory or
muscular disease. Twelve patients, 5 men and 7 women, with ages ranging from 19 to 41 years, who received
corticosteroids for diseases other than respiratory were recruited into two groups: 6 patients were assigned to the control group and got
sham training and 6 patients received SIMT while receiving
corticosteroids in a single-blind group-comparative trial. In both groups, there was no difference between the post-treatment and pretreatment values as regard to the FEV1/FVC relationship. However, in the control group but not in the training group, there was a small but significant decrease, from 99.2 +/- 3.0 to 94.3 +/- 2.8 (mean +/- SEM, p < 0.01) in FEV1 (percent of predicted normal values) and from 103.5 +/- 4.0 to 88.7 +/- 3.1 (p < 0.001) in the FVC, following treatment. All subjects had normal inspiratory muscle strength, as expressed by the maximal inspiratory mouth pressure (PImax) at residual volume, and inspiratory muscle endurance as expressed by the relationship between peak pressure and the PImax before treatment. Following administration of
corticosteroids, there was a gradual decrease in both inspiratory muscle strength (from 117.5 +/- 9.4 to 80.5 +/- 3.3 cm H2O, p < 0.005) and endurance (from 82.7 +/- 2.6 to 40.2 +/- 1.7%, p < 0.001) in the control group. On the contrary, despite
corticosteroid therapy, there were no significant changes in the inspiratory muscle function in the patients whose inspiratory muscles were specifically trained. We conclude that
corticosteroids have a significant deteriorating effect on respiratory muscle function in humans. This weakness is preventable by using SIMT during
corticosteroid treatment.