Statistics from Altmetric.com
The editorial by Dr Gardner1 on controversial aspects of the hyperventilation syndrome (HVS) refers to our study2 in the same issue ofThorax. This study showed that patients with HVS have an accentuated increase in ventilation as a response to change in body position from supine to standing. The editorial was a valuable addition to this difficult subject. We feel, however, that the interpretation of our paper in the editorial did not quite match the purpose or the message of the original study.
We agree with Dr Gardner that the definitions of HVS in the literature are unfortunately variable. Dr Gardner suggests that the term HVS should be abandoned and that efforts should be made to find the initiating and sustaining causes of hyperventilation. This is also our strategy, so the subjects in our study underwent a comprehensive set of cardiopulmonary examinations. In clinical practice, however, the aetiology of hyperventilation often remains unknown and the only finding may be a disproportionate ventilatory pattern with resulting hypocapnia and alkalosis which may (at least partly) be the sustaining cause of the symptoms. Why would we not call the disorder HVS? An alternative label would be “unknown dyspnoea” which does not assure the patient of the benign nature of the disorder. Dr Gardner suggests that our subjects “fit into a classification of dyspnoea and air hunger with secondary intermittent hyperventilation”. This classification would probably include the whole spectrum of differential diagnoses of dyspnoea and it is not justified, when several diagnostic procedures have been performed, to exclude cardiopulmonary diseases when the hyperventilatory component of the disorder has been objectively documented. In contrast to Dr Gardner, we also believe that the finding of hyperventilation may be of importance when the initiating cause is known, since not all patients with cardiopulmonary diseases have such a tendency. The disproportionate compensatory mechanisms of ventilation and the resulting hypocapnia may therefore be a sign of inherent susceptibility to hyperventilation and may be responsible for part of the patients' symptoms.
In our study2 the organic causes of dyspnoea were excluded as far as possible by specialist care in a university hospital. For the assessment of eventual panic disorder, symptom criteria described by the World Health Organization for research were used. Contrary to what Dr Gardner states in his editorial, the diagnosis of HVS in the study was based on episodic symptoms typical of HVS and documented respiratory alkalosis (with concomitant hypocapnia) in the arterial blood during such an episode. We consider this to be close to the original definition by Geisler et al.3 The approach to the definition of HVS was therefore physiological and unambiguous. As this was clearly described in the study, it is difficult to understand the confusion by Dr Gardner when he claims that the diagnosis was made in the presence of normal Paco 2. The measured orthostatic response which was the object of investigation is another matter and should not be confused with the process of diagnosis.
Finally, we would point out that the main purpose of our paper was to describe the accentuated breathing response to orthostatic changes in patients with HVS. We hope that this finding will add to the knowledge of the causes and mechanisms of hyperventilation called for by Dr Gardner. Contrary to the repeated claim in his editorial,1 our intention was not to present the orthostatic test as a “diagnostic criterion for HVS” nor as a basis for its diagnosis—assessment of these patients is much more complicated. Instead, we stated that measurements of pulmonary gas exchange during the orthostatic test “are/may be useful in the clinical evaluation of patients with hyperventilation disorders”. However, based on our results and clinical experience over 15 years, we believe that this test is, indeed, helpful as part of the diagnostic evaluation of HVS.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.