Lung function and respiratory muscle strength after propranolol in thyrotoxicosis.

Thirty-five thyrotoxic patients were assessed before treatment, after treatment with propranolol, and after antithyroid drugs. The first group of patients (n = 17) performed the following tests at all three assessment points: forced expiratory volume in the first second (FEV1), vital capacity (VC), functional residual capacity (FRC), residual volume (RV), total lung capacity (TLC), maximal mid-expiratory flow rate (MMFR), diffusing capacity for carbon monoxide (DLCO), and maximum static inspiratory and expiratory mouth pressures (PImax and PEmax). Arterial blood gas analysis was also performed for the first group of patients. No significant changes were seen either after propranolol or after antithyroid drugs in the FRC, RV, TLC, MMFR, DLCO, or blood gases. The remaining 18 patients, group 2, performed only the FEV1, VC, PImax, and PEmax tests at each assessment. The only index of respiratory function that improved significantly after propranolol was PImax (from 46.5 +/- 16.5 to 53.2 +/- 22 cmH2O, p less than 0.01). This suggests that adrenergic excess may play a role in thyrotoxic inspiratory muscle weakness. After antithyroid drugs, PImax, PEmax, FEV1, and VC all increased significantly as expected.