THE EFFECT OF CORTICOSTEROIDS ON INSPIRATORY MUSCLE PERFORMANCE IN HUMANS

Functional alterations in the inspiratory muscles were evaluated in pa tients receiving corticosteroids for diseases other than respiratory. Inspiratory muscle strength, as expressed by the maximal inspiratory m outh pressure (PImax), and inspiratory muscle endurance (PmPeak/PImax) , using a pressure threshold breathing device, were evaluated in eight patients with normal pulmonary and inspiratory muscle functions (two patients with rapidly progressive glomorulonephritis, two with glomoru lonephritis with minimal changes, two with idiopathic thrombocytopenic purpura, and two with subacute thyroiditis). There was a gradual decr ease in both inspiratory muscle strength and endurance following corti costeroid administration. After 8 weeks of treatment PmPeak/Pimax decr eased from 84.4 +/- 2.4 to 67.9 +/- 3.1 percent (p<0.001), while inspi ratory muscle strength dropped from 126.9 +/- 9.6 to 86.5 +/- 7.4 cm H 2O (p<0.005). Gradual steroid dosage tapering resulted in marked impro vement in both strength and endurance; the inspiratory muscle strength rose significantly to 112.2 +/- 8.1 cm H2O (p<0.0005) when steroid tr eatment was stopped, and even more significantly 6 months later (to 12 3.1 +/- 8.1 cm H2O [p<0.0001]), and the PmPeak/Pimax rose to 60.6 +/- 3.4 percent (p<0.001) and to 74.7 +/- 3.2 percent (p<0.0001), respecti vely. We conclude that corticosteroids have a significant deterioratin g effect on respiratory muscle function in humans. This weakness is re versible while tapering steroid dosage. Steroid therapy should be reco nsidered in patients with underlying lung disease.