In his comprehensive review of the hyperventilation syndrome1 Gardner points out the difficulties in terminology and definition that have dogged this complicated and confused area. As he states, it is physiologically inappropriate to use the term “hyperventilation” in the absence of demonstrated hypocapnia. The term “hyperventilation syndrome” has, however, gained wide currency both in research studies and in clinical practice, often without precise diagnostic criteria being specified or hypocapnia rigorously demonstrated. This situation may have arisen from the perception of many clinicians that there is a real but poorly defined clinical entity causing morbidity in real world practice resulting from breathing abnormalities. Abnormal breathing patterns may, indeed, result in hyperventilation and hypocapnia, but rapid, irregular and shallow breathing may not necessarily result in increased ventilation yet may still cause significant symptoms. Isocapnic hyperventilation studies have shown that many of these symptoms are independent of hypocapnia,2 and other mechanisms have been suggested.3 Other descriptive labels have been applied to patients with characteristic symptoms associated with breathing abnormalities, with or without hypocapnia, such as “disproportionate breathlessness”, “air hunger”, and “behavioural breathlessness”, but these terms have not gained widespread acceptance. Van Dixhoorn has used the term “dysfunctional breathing” to describe the production of symptoms directly as a result of abnormal breathing patterns.4 We are used to considering functional problems in other physiological systems but have not applied this concept to breathing until recently. The diagnosis of dysfunctional breathing may be suggested by characteristic symptom patterns and clinical pictures but, as Gardner points out, these symptoms are all non-specific. Ultimately the verification of the label must lie in the response to breathing retraining interventions in these patients. This umbrella term allows inclusion of patients with and without hyperventilation, and moves the focus of attention from physiological hypocapnia to pragmatic clinical responses.

Gardner points out that the “hyperventilation syndrome” has been associated with other conditions, including psychiatric syndromes and asthma. The association of dysfunctional breathing with asthma may explain the anecdotal success of interventions which rely on breathing retraining, such as the Buteko method, to improve patients' well being. Studies are needed to clarify the presence of abnormal breathing in common and important clinical situations and to objectify anecdotal reports of responses to breathing retraining interventions.