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Recent insights into hyperventilation from the study of Rett syndrome
  1. Alison M Kerra,
  2. Peter O O Julub
  1. aAcademic Centre, Department of Psychological Medicine, Glasgow University, Gartnavel Royal Hospital, 1055 Great Western Road, Glasgow G12 0XH, UK, bAutonomic Unit, Department of Neurophysiology, Central Middlesex Hospital, Acton Lane, London, UK
  1. A Kerr

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The medical literature presents two major groups of disorder in which hyperventilation is a presenting feature. Disorders of mood, notably panic disorder, and disorders of brain stem function—developmental, vascular, traumatic, toxic, metabolic, degenerative or neoplastic. References to the underlying brain morphology leading to these conditions are few and imprecise, perhaps reflecting the inaccessibility of the brain stem to clinical medicine and the complexity of the neural basis of respiratory control. Even in Joubert’s syndrome, where hyperventilation is a major feature, hypoplasia of the cerebellar vermis and cyst of the fourth ventricle have been described but the exact pathophysiology is unclear.1

The clinical medical literature gives more space to discussing the effects of hyperventilation, including the well known respiratory alkalosis with reduction in plasma ionised calcium, tingling sensations, tetany, induction of epileptic seizures, and induction of interictal epileptogenic activities seen on the electroencephalogram (EEG). In healthy children, especially girls, voluntary hyperventilation produces slow EEG waves, usually generalised over the cerebral cortex. Hyperventilation reduces oxygen delivery to the brain,2 and cardiac repolarisation abnormalities including ST depression and T wave inversion have been described.3

From its delineation in 1937 to the 1980s, the “hyperventilation syndrome” was held responsible for much of the symptomatology of panic disorder4; however, with increased accuracy of measurements, this notion was replaced by the view that autonomic instability underlies both hyperventilation and panic disorder.5 Although there is a clear association between panic and hyperventilation, the neurological basis for this is still unresolved.

Physiology of hyperventilation

Hyperventilation or overbreathing is variously defined, according to the measures available and familiar to each scientific discipline. There is agreement that the breathing exercise must ventilate the lungs in excess of metabolic requirements at that particular point in time and thus induce measurable changes, usually a reduction in arterial or alveolar …

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