Respiratory troubles are rarely a serious complaint in hypothyroid patients. However, hypothyroidism may cause respiratory problems through: (1) depression of the respiratory centre in the brain; (2) disturbed neural conduction and/ or neuromuscular transmission to the respiratory muscles (due to hypothyroid neuropathy); (3) diseased respiratory muscle function (due to hypothyroid myopathy); and (4) changes in the alveolar- capillary membranes and the surfactant lining the alveoli, leading to impaired gas exchange. Fatigue and dyspnoea on exertion are frequent symptoms. Dyspnoea is a frequent complaint of myxoedematous patients, but is also a common symptom among well people. Congestive heart failure of separate origin, pleural effusion, anaemia, obesity, or pulmonary disease may be responsible.

Some information on pulmonary function in hypothyroidism is available. Wilson and Bedell found a normal vital capacity and arterial PCO₂ and PO₂ in 16 hypothyroid patients. They also found a decreased maximal breathing capacity, decreased diffusion capacity, and decreased ventilatory response to carbon dioxide. Decreased ventilatory drive is present in about one- third of hypo thyroid patients, and the response to hypoxia returns rapidly within a week after beginning therapy. Summarizing the few studies, there is little abnormality of resting pulmonary function in most non- obese patients with hypothyroidism. Some patients may exhibit a decreased vital capacity, probably due to muscular weakness. Overall oxygen transfer may be slightly decreased, as evidenced by a decreased PO2, possibly due to a decreased diffusing capacity for carbon monoxide. An increase in ventilation perfusion mis matching or an opening of anatomical shunts may also contribute to these modifications.

The severity of hypothyroidism parallels the incidence of impaired ventilatory drive. Patients with myxoedema may develop carbon dioxide retention, and carbon dioxide narcosis may be a cause of myxoedema coma. Hypothyroidism- induced breathing disorders during sleep, particularly sleep apnoea syndromes (OSAS), have been described. Obstructive sleep apnoea has been documented in hypothyroidism in about 30% of patients and is reversible with treatment. Hypothyroidism may predis pose to upper airway obstruction by several mechanisms: increased size of the tongue and other pharyngeal skeletal muscles; a slow and sustained pharyngeal muscle contraction pattern; or diminished neural output of the respiratory centre. After LT4 replacement therapy, apnoea periods, oxygen desaturation events, and snoring usually improve. Myxoedematous patients are more subject to respiratory infections. Pleural effusions usually are evident only on radiological examination.

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مواضيع ذات صلة

Organ System Manifestations of Hypothyroidism: Cardiovascular Changes

Organ System Manifestations of Hypothyroidism : Cutaneous Manifestations and Changes in the Connective Tissues

Thromboembolic Conditions

Conditions that Cause Excessive Bleeding in Humans

Absent Intrinsic Factor Secretion and Pernicious Anemia

Subclinical Hyperthyroidism

Thyrotoxic Periodic Paralysis: Clinical Features

Nutritional Causes of Folate Deficiency

Neurologic Dysfunction with Cobalamin Deficiency

Sclerosing Thyroiditis (Riedel’s Thyroiditis) : Clinical Features

Infectious Thyroiditis

Leukopenia