Original ArticleSubjective symptoms and breathing pattern at rest and following hyperventilation in anxiety and somatoform disorders
Introduction
The diagnosis of hyperventilation syndrome (HVS) and of anxiety disorders is primarily clinical and based on the presence of a number of somatic and psychological symptoms, which cannot be explained by an organic disorder. The symptoms suggestive of HVS (Nijmegen Questionnaire) [1] and of anxiety disorders (specifically panic disorder, DSM-III-R) [2] are nearly identical. Whereas the DSM classification is merely descriptive, the diagnosis of HVS implies a judgment on causation of the symptoms. Therefore, additional requirements of a respiratory nature have been proposed for its diagnosis: (a) the symptoms should be reproduced in whole or in part by voluntary hyperventilation producing hypocapnia (the so-called “hyperventilation provocation test,” or HVPT) [3]; and (b) a delay in the recovery of end-tidal CO2 concentration (FETCO2) following the HVPT should occur 4, 5. However, the specificity and validity of both the HVPT as a diagnostic tool and of delayed recovery have recently been challenged 6, 7, 8. In addition, because ambulatory capnometry produced little specific evidence for the causal involvement of hypocapnia in the symptoms [7], the usefulness of the HVS as a diagnostic concept has been questioned. In addition, HVS should not be viewed as an explanatory alternative for panic disorder.
In a recent study comparing healthy subjects and patients with HVS and/or anxiety disorders, we suggested that the diagnostic value of ventilatory parameters and FETCO2 improved when the features of breathing at rest and following HVPT were combined [9]. Indeed, the measurement context itself is often experienced as stressful, which may induce some of the typical respiratory and subjective responses in HVS patients during the baseline measurement [9]. Because the delayed recovery test takes baseline data as points of reference, its specificity for the diagnosis of HVS may be reduced. In addition, the usefulness of the HVS concept has been questioned because the subjective symptoms were not clearly linked with hypocapnia [7], but dysfunctional breathing may cause symptoms through mechanical processes as well [10]. Finally, other studies in our group have documented the role of occasional respiratory challenges as a source of learning of perceptual–cognitive processes, which eventually blur the relationship between hypocapnia and hypocapnia-related symptoms 11, 12. All this suggests that neither the subjective recognition of the symptoms after the HVPT nor the presence or absence of hypocapnia during a typical bout of symptoms should be viewed as critical to judge the importance of respiratory abnormalities in HVS or anxiety disorders. Recent data have provided further evidence, at least for a hyperventilation subtype of panic [13].
In this study, we investigated a large number of patients, complaining of symptoms supposedly caused by regular hyperventilation. They were also grouped on the basis of DSM-III-R criteria into panic disorder, other anxiety disorders, and somatoform disorders. The symptoms and the breathing pattern and FETCO2 at rest and following HVPT were compared with those of a group of healthy subjects. Principal components analysis was used to group the variables on the basis of their mutual correlations into a number of independent factors. One principal components analysis was carried out on the set of breathing variables at rest and after HVPT, and another one on the set of subjective symptoms in daily life and after HVPT. This type of analysis served three purposes:
- 1.
Evaluation of the importance of the HVPT as a diagnostic tool. If, as a result of the analysis, symptoms during daily life are grouped with the same symptoms produced by the HVPT, it suggests that the daily-life symptoms can be reproduced by the HVPT and may be mediated by the same process. Conversely, if symptoms in daily life and the same symptoms following HVPT are grouped into different factors, it is likely that they are not linked by the same mechanism and, consequently, that their presence following HVPT cannot be used for diagnosis of these symptoms in daily life. Exploratorily, we also analyzed the breathing variables at rest and after the HVPT in the same way.
- 2.
The individual scores on the various factors allowed comparison of means of the diagnostic groupings: HVS or DSM-III-R vs. healthy subjects. Any factor not related to these classifications is not diagnostically useful.
- 3.
Finally, the extent to which specific diagnoses are identified by means of the scores of the factors of the analysis is suggestive of the contribution of the symptoms and breathing variables to the diagnoses.
Section snippets
Subjects
Nine hundred three patients (386 men) and 170 healthy subjects (86 men) were investigated. The patients were referred to the laboratory because they presented with symptoms that could not be explained by an organic disease and were suggestive of HVS. Healthy subjects were recruited as volunteers from outside the hospital and were not informed about the purpose of the study. The age range was between 19 and 62 years. A few subjects were not able to complete the tests and were excluded.
Diagnosis
Patients
Scores of STAI and Nijmegen Questionnaire
Table I lists, in addition to the mean ages, the mean scores of STAI-S, STAI-T, and Nijmegen (NVL) Questionnaires. Patients reported more state and trait anxiety and more symptoms than normals. The classification of patients into panic, other anxiety disorders, and somatoform disorders explained 23%, 31%, and 32% of the total variance in STAI-S, STAI-T, and NVL, respectively.
Symptoms
Ten factors were derived by the principal components analysis from the 16 daily-life symptoms and 29 symptoms during
Discussion
The results of the present study will be discussed in relation to the three questions mentioned in the Introduction: Does the HVPT contribute to diagnosis? How do the diagnostic categories differ in regard to symptoms and breathing pattern? To what extent do symptoms and breathing patterns contribute to the specific diagnoses? The first question was investigated by means of a principal components analysis combining the symptoms in daily life and data at rest with the corresponding symptoms and
Conclusion
The present study investigated the diagnostic value of subjective symptoms in daily life and after a HVPT and of the breathing pattern at rest and during recovery of the HVPT for two classifications of patients: HVS or DSM-III-R. The same variables distinguished normals and patients, regardless of which categorization was used. Patients with panic differed from other patients with anxiety disorders by an increased level of symptoms and FETCO2 decline at rest. The HVPT may be considered
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