Hypothyroidism is defined as a clinical state resulting from insufficient

secretion of thyroid hormone from thyroid gland due to some structural or

functional impairment of thyroid hormone production. Hypothyroidism affects

several organs systems. Clinical symptoms of hypothyroidism include fatigue,

depression, weakness, modest weight gain, cold intolerance, disturbed sleep,

dry coarse hair, constipation, dry skin, muscle cramps, poor concentration, less

memory, irregular and inconsistent menstrual cycle etc. All such signs and

symptoms are recovered after replacement of thyroid hormone (Larsen, 2003).

Studies have shown that both myxoedema and hypothyroid state produce

depression of hypoxic ventilator drive which is responsive to replacement

therapy. This alteration in ventilator control may contribute to the

hypoventilation seen in myxoedema and hypothyroidism (Zwillich, 1975).

Hypothyroidism affects respiratory muscle strength which is linearly related to

the thyroid hormone levels. Muscular weakness is present in both inspiratory

and expiratory muscles and is reversible with treatment (Siafakas, 1972).

Studies have shown that sleep pane episodes are common in person with

untreated hypothyroidism even with normal lung function. Thyroxin

replacement therapy decreases apnea frequency, even without change in body

weight (Larsen, 2003).