Neurologic manifestations of pulmonary disease

Respiratory insufficiency of any cause has significant effects on the nervous system. Headache, mental status changes, papilledema, and numerous motor abnormalities including asterixis are commonly seen. Abnormalities in ventilation and gas exchange result in hypoxia, hypercapnia, and respiratory acidosis, and these, in turn, interfere with cerebral metabolism, increase CBF, and may raise intracranial pressure. Chronic respiratory insufficiency can persist for many months with minimal neurologic symptoms, as numerous compensatory mechanisms, particularly renal, may take effect. Treatment includes restoring adequate ventilation and improving gas exchange and may require tracheal intubation and assisted ventilation. Supplemental oxygen therapy should be carefully monitored, as high rates of flow may suppress the hypoxic drive for respiration and lead to significant carbon dioxide retention. The sleep apnea syndromes are a group of disorders in which abnormal respiratory patterns during sleep result in hypercapnia and hypoxemia. Intermittent obstruction of the upper airway and abnormalities of brainstem respiratory centers cause frequent nocturnal awakenings and apneas in these patients. Treatments vary and include weight loss in obese subjects, respiratory stimulants, tracheostomy, and diaphragmatic pacing. Rapid ascent to high altitudes may result in headache, changes in mental status, papilledema, and other neurologic symptoms in certain individuals: a syndrome known as high-altitude sickness. Hypoxia leading to cerebral edema, nocturnal periodic breathing, and hypobaria produces neurologic symptoms in these individuals. Acetazolamide and dexamethasone may be effective in minimizing symptoms of this disorder. Sustained hyperventilation produces acral and circumoral paresthesias and lightheadedness in anxious individuals and can be maintained by relatively normal ventilatory patterns once established. These symptoms are due to hypophosphatemia and respiratory alkalosis, the latter reducing CBF and causing localized tissue hypoxia. Rebreathing into a paper bag at the first awareness of symptoms is the most effective form of treatment.