RESPIRATORY MUSCLE STRENGTH IN HYPERTHYROIDISM BEFORE AND AFTER TREATMENT

We undertook this study to investigate respiratory muscle strength in relation to thyroid function in 20 thyrotoxic patients and in a group of 20 normal subjects matched for age and sex. Global respiratory muscle strength was assessed by measuring mouth pressure during maximal static inspiratory (PImax) and expiratory (PEmax) efforts. We also measured VC, FVC, and FEV1 as well ss thyroid-related hormones (T3, T4, TSH). Measurements were made once in normal subjects and twice in thyrotoxic patients, before and 3 months after medical treatment. Our results showed that both maximal pressures were significantly reduced (p < 0.0001) before treatment in thyrotoxic patients in relation to the mean values of the normal subjects (p < 0.0001), and they increased significantly (p < 0.0003) after treatment. Lung volumes were significantly reduced (p < 0.0001) before and increased significantly (p < 0.008) after treatment. The ratio FEV1/FVC did not change. A statistically significant linear relationship was found when PImax of patients with thyrotoxicosis before treatment and of normal subjects were plotted against thyroid hormones (T3, T4) (r = -0.746 and r = -0.745, respectively, p < 0.001). Similarly, a statistically significant linear relationship was found between PEmax and T3 and T4 (r = -0.837 and r = -0.838, respectively, p < 0.001). No relationship was found between maximal pressures and TSH. Finally, a significant linear relationship was found between Pimax and PEmax (r = 0.872, p < 0.001). Our results confirm that in thyrotoxicosis respiratory muscle weakness occurs that affects both inspiratory and expiratory muscles. Furthermore, our results demonstrated that respiratory muscle strength was proportional to the degree of thyroid dysfunction. Respiratory muscle weakness was reversible with medical treatment.