hyperventilation /-ven′tilā″shən/ [Gk, hyper + ventilare, to fan] , pulmonary ventilation rate greater than that metabolically necessary for gas exchange, resulting from an increased respiration rate, an increased tidal volume, or both. Hyperventilation causes an excessive intake of oxygen and elimination of carbon dioxide and may cause hyperoxygenation. Hypocapnia and respiratory alkalosis then occur, leading to dizziness, faintness, numbness of the fingers and toes, possibly syncope, and psychomotor impairment. Causes of hyperventilation include asthma or early emphysema; increased metabolic rate caused by exercise, fever, hyperthyroidism, or infection; lesions of the central nervous system, as in cerebral thrombosis, encephalitis, head injuries, or meningitis; hypoxia or metabolic acidosis; use of hormones and drugs, such as epinephrine, progesterone, and salicylates; difficulties with mechanical respirators; and psychogenic factors, such as acute anxiety or pain. Compare hypoventilation. See also respiratory center.
