The paper by Malmberg et al in the current issue of Thorax 1 deals with the difficult subject of the hyperventilation syndrome and finds that these patients have a disproportionately high ventilatory response to change of body position from supine to standing. The authors suggest that this can be used as a diagnostic criterion for hyperventilation syndrome. Hyperventilation is a confused and poorly documented subject and the publication of this paper provides an opportunity to review some of the particularly controversial aspects of this subject.

The first issue concerns the basis for the labelling of these patients as “hyperventilation syndrome”. Some of the controversies about the use of this term have recently been reviewed by Folgering2and by Gardner.3 The physiological definition of hyperventilation is alveolar ventilation that is inappropriately high for the metabolic production of carbon dioxide, leading to reduction of arterial Pco₂ (Paco ₂) below the normal range (hypocapnia) and respiratory alkalosis. The combination can lead both to vasoconstriction in selected vascular beds and to neuronal hyperexcitability producing symptoms involving most systems of the body. Many psychosomatic syndromes have been described in the past in which hyperventilation has a variable and uncertain role but the term “hyperventilation syndrome” was first used in 1938 to describe patients with the somatic symptoms of both hypocapnia and anxiety.4 This theme was extended by subsequent authors5-7 and the definition arrived at by Lewis and Howell in 1986 on the basis of a questionnaire of delegates at a psychophysiology meeting8 was “a syndrome induced by physiologically inappropriate hyperventilation and usually reproduced in whole or in part by voluntary hyperventilation”. However, the term “hyperventilation syndrome” is now used in so many different contexts that it could be argued that it has ceased to have any universal meaning. …