What Is Alveolar Hypoventilation;Diagnosis,Treatment And Prognosis

The term primary or idiopathic alveolar hypoventilation denotes a rare clinical syndrome occurring in patients with normal pulmonary and thoracic cage mechanics in whom the primary abnormality is alveolar hypoventilation. It is sometimes referred to as Ondine’s curse. The syndrome is characterized by symptoms of headache, drowsiness, or somnolence, exertional dyspnea, and signs of cyanosis and congestive heart failure.

Etiology of Alveolar Hypoventilation

The causes of this syndrome are not known. Resistances to breathing and respiratory muscular power are essentially normal, which distinguishes it from hypoventilation occurring in chronic bronchitis, in neuromuscular disorders, in skeletal abnormalities of the thorax, e.g., kyphoscoliosis, or in extreme obesity. Associated central nervous system disorders, such as the sequelae of encephalitis, neurosyphilis, and mental retardation with or without epilepsy, have been reported in over half the patients, but no specific lesions have been found in the region of the respiratory center at autopsy. Alveolar hypoventilation has also been reported in a small proportion of patients after bulbar poliomye- litis, sometimes many years after apparent recovery, and it seems likely that in these patients central nervous system disease is responsible.

Diagnosis of Alveolar Hypoventilation

The aforementioned findings in the absence of other disorders of the lungs and thorax are highly suggestive of idiopathic alveolar hypoventilation. This diagnosis is supported if the patient can temporarily restore the blood gas tensions to normal by a period of voluntary hyperventilation, Differential diagnosis includes ocher causes of congestive cardiac failure, cyan- osis, polycythemia, and somnolence, the most common being chronic obstructive bronchitis (“blue bloater” form) and cyanotic congenital heart disease; the syndrome may also be confused with primary polycythemia or narcolepsy. Severe metabolic alkalosis caused by pro- longed vomiting, as in anorexia nervosa or chronic pyloric stenosis, may be accompanied by severe hypoventilation. It is not certain whether the cardiorespiratory failure of extreme obesity is an essentially different disorder or not.

Alveolar Hypoventilation Treatment.

Treatment of congestive cardiac failure usually improves the ventilatory failure as well. Oral diuretic therapy with, for example, chlorothiazide, 1 gram, or furosemide, 40 to 80 mg daily; venesections to reduce the hematocrit to between 50 and 55 per cent; and digoxin, 0.25 mg once or digitoxin 1 mg daily will reduce pulmonary congestion and peripheral edema, with im- provement in arterial Pco.! and 100.2. Sometimes, when these measures are not successful, a short period of ar- tificial or assisted ventilation to reduce the arterial Pco.2 and raise Poz may be ibllowed by prompt diuresis.

Cuirass ventilators permit ventilation to be assisted without endotracheal intubation, and in some patients regular artificial ventilation at night in a cuirass ventilator may maintain them in an improved state. Attempts to increase ventilation with acetazolamide, progesterone, aminophylline, and analeptics have not been successful. Instruction in voluntary increased breathing and electrophrenic stimulation with surface electrodes have been successful in the short term only. All other abnormalities likely to hinder breathing, e.g., bronchitis, asthma, and obesity, should be treated as effectively as possible. If upper airway obstruction occurs during sleep despite weight reduction and withdrawal of all central nervous system depressant drugs, tracheostomy should be considered.

Alveolar Hypoventilation Prognosis.

There is insufficient information at present to estimate the prognosis with accuracy. Without effective treatment of congestive cardiac failure, the prognosis is very poor. With treatment, patients may continue in reasonable health for several years, requiring only intermittent therapy for acute pulmonary infections and venesections if polycythemia becomes severe. One patient has been reported to have maintained normal arterial PC02 for nine months after three years of continuous hypercapnia and repeated episodes of ventilatory and cardiac failure; this was attributed to voluntary increase in ventilation.

by Abdullah Sam
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