[Cardiopulmonary involvement in thyroid gland diseases]

Thyroid hormones exercise a direct influence on the lung and myocardium. It has been found that at the heart of patients suffering from hyperthyroidism there is an increased production of contractile proteins and a redistribution of myosin Isoenzymes. Reduced efficiency results from the increased oxygen consumption and insufficient adaptation of the heartbeat to stress. Thyroid hormones are responsible for reducing arterial resistance; a higher incidence of supraventricular arrhythmias has been observed. In contrast, the cardiac changes in hypothyroidism are associated with an enhanced deposition of glycosaminoglycan in the myocardium. Besides bradycardia and low voltage there is an increased incidence of pericardial, pleural and peritoneal effusions with high protein content. Patients suffering from hypothyroidism have a higher incidence of atherosclerotic changes. Hypothyroidism is associated with a reduction of the beta-adrenergic receptors, and hence disturbances of rhythm are rare and do not increase even under substitution therapy. Pulmonary involvement in hyperthyroidism is evident from an enhanced respiratory minute volume, a reduced vital capacity, and dyspnoea at rest. In patients suffering from hypothyroidism, hypoventilation reduces the efficiency. Over and above this, myopathic changes of the respiratory muscles have been described. Involvement of thyroid hormones in the maturing of type II pneumocytes and of the surfactant factor has also been under discussion.