Abstract
Hyperventilation Syndrome (HVS) is a functional breathing disorder characterised by recurrent or chronic changes in breathing pattern causing respiratory and non-respiratory complaints that cannot be attributed to any specific medical diagnosis. HVS is thought to be common yet often unrecognised or misdiagnosed as ‘difficult-to-control’ asthma. HVS can co-exist with asthma and is also a differential diagnosis of asthma. There are also similarities and overlaps between HVS and anxiety disorders. There is no gold standard for the diagnosis of HVS, but the Nijmegen Questionnaire (NQ), a 16-item symptom checklist for HVS symptoms, is most commonly used in both clinical and research settings. A high NQ indicates HVS. However, this questionnaire includes several symptoms that are also associated with asthma and anxiety disorders. This casts doubts as to whether the NQ can distinguish HVS as a distinct clinical entity. Some view HVS as undiagnosed asthma, while others consider that it is a form of panic disorder. The aim of this thesis was to explore the overlap of HVS with asthma and anxiety in a general population sample.
The prevalence of HVS and its association with asthma diagnosis, symptoms, objective markers of severity, and anxiety diagnosis at age 38 years were studied in the Dunedin Multidisciplinary Health and Development Study, a longitudinal investigation of 1,037 individuals born between 1972 and 1973 in Dunedin, New Zealand.
Nearly one in 10 Study members had HVS according to the NQ and it was approximately twice as common in women as men (12.1% vs. 6.5%, respectively; P = 0.003). There was a substantial overlap between HVS and asthma with up to one-third of asthmatic women (35.4%) and one-eighth of asthmatic men (13.5%) potentially affected with co-morbid HVS. A different pattern of NQ symptom scores was found in people with only HVS compared to that of people with only asthma. Additionally, the objective markers of asthma including FEV1/FVC ratio and bronchodilator response differed significantly between those with only HVS and those with only asthma, suggesting that HVS can be distinguished from asthma using the NQ and is not merely undiagnosed asthma that is falsely detected by the NQ due to overlapping symptoms. Asthmatics with high NQ scores showed higher symptom scores for all 16 NQ items, rather than scoring high only for the asthma-like symptoms suggesting that these high NQ scores represented co-morbid HVS rather than more severe asthma. Further, there were no differences observed in the objective markers of asthma between those with both asthma and HVS and those with asthma alone. A large overlap was also found between HVS and anxiety disorders, especially with panic disorder (PD). The high NQ scores found in those with both HVS and panic disorder could not solely be explained by co-morbid panic disorder diagnosis: despite a large overlap in symptoms, only approximately half of the total NQ score could be attributed to panic disorder and HVS is thus likely to be distinct from panic.
This is the first descriptive study of the prevalence and the overlap of HVS with asthma and anxiety in a large population-based sample. A substantial number of young adults in the general population have HVS and it is more common in those with asthma or anxiety disorders. It is important to assess for, and recognise HVS in these contexts.