Dyspnoea, lung function & respiratory muscle pressures in patients with Graves' disease

To understand the pathophysiology of dyspnoea in patients with hyperthyroidism, lung function, maximum inspiratory, expiratory respiratory muscle pressures (MIP and MEP) and intensity of dyspnoea (after six minutes walking test) were recorded in 12 consecutive patients with active Graves' disease. Reassessment was done after achieving euthyroidism with 8-12 wk of carbimazole therapy. Patients covered similar distance during 6 min walking before and after carbimazole therapy. However, there was a significant reduction in dyspnoea following euthyroidism. This was accompanied by significant decrease in respiratory rate, minute ventilation, forced expiratory volume in one second (FEV1%) and improvement in the forced vital capacity (FVC). No significant changes in tidal volume (TV) and maximum-midexpiratory flow rates (MMEFR), MIP and MEP were observed. Lung function parameters, MIP and MEP did not correlate with the severity of dyspnoea. Serum T4 levels correlated inversely with the distance covered during 6 min walking test, MIP and MEP. To conclude, increased breathing effort in presence of reduced FVC may lead to dyspnoea during hyperthyroid phase in patients with active Graves' disease. Lack of correlation between the severity of dyspnoea and abnormalities in lung function suggests that other mechanisms of dyspnoea may also operate in these patients.