Ventilatory Control in Myxedema and Hypothyroidism

Abstract

Alveolar hypoventilation is known to occur in myxedema. To clarify the role of hypoxic ventilatory drive and hypercapnic ventilatory drive in thyroid hormone insufficiency states, 10 patients with myxedema and seven with hypothyroidism (thyroid ablation) were studied before and after thyroid replacement. An index developed for hypoxic ventilatory drive was markedly reduced in myxedema: 17 ± 4.7 (S.E.M.) (normal, 126 ± 8.7) (p < 0.01) and increased to 78 ± 12.6 (p = 0.02) with thyroid hormone replacement. In the hypothyroid group this index was also depressed as compared to normal at 67 ± 20 (p < 0.01) and increased to 114 ± 19 (p < 0.02) with replacement.

An index for hypercapnic ventilatory drive was depressed in myxedema, 0.69 ± 0.13, as compared to a normal value of 1.88 ± 0.13 (p < 0.01), but was not significantly depressed in hypothyroidism. With thyroid hormone replacement this index did not significantly increase in either group.

We conclude that both myxedema and hypothyroid states produce depression of hypoxic ventilatory drive that is responsive to replacement therapy. This alteration in ventilatory control may contribute to the hypoventilation seen in myxedema. (N Engl J Med 292:662–665, 1975)