Chronic Hyperventilation in Asthma

Background: The prevalence of hyperventilation resulting in an abnormal low PaCO2 is well recognised as a concomitant feature of acute asthma. In a more stable state of disease, the prevalence of hyperventilation and dysfunctional breathing has been extensively studied with questionnaires. By contrast, only few studies examined this phenomenon with blood gas analysis. Aims: Aim of this study was to determine the prevalence of (chronic) hyperventilation in patients with asthma verified on the basis of blood gas analysis. Methods: Upon referral by their general practitioner to a pulmonologist, patients with asthma underwent arterialized blood gas analysis, pulmonary function testing and completed the Asthma Control Questionnaire (ACQ), Asthma Quality of Life Questionnaire (AQLQ) and the Nijmegen Questionnaire (NQ). Results: In a total of 605 patients, it was found that 145 (24.0%) had a chronic hyperventilation (CHV) blood gas (PCO2<4.7 and bicarbonate <23) and 46 (7.6%) an acute hyperventilation blood gas. Patients with chronic hyperventilation were significantly more often female (110 versus 35, P<0.001), were younger (42.7±15.5 to 47.0±16.2 years, P<0.001 and had higher FEV1%pred. (91.5±16.2 to 87.9±16.7) compared to patients without hyperventilation. By contrast, BMI, smoking status, ACQ scores, AQLQ scores and exacerbation frequency were not significantly different. NQ scores could not discriminate for (chronic) hyperventilation in this group of patients (χ2 0.35, LLR 0.22). Conclusion: In 605 asthma patients, chronic hyperventilation was present in 145 (24%) of the cases. Patients with chronic hyperventilation were younger and predominantly of the female sex, with better FEV1%pred. NQ appeared not to be a valid tool to use as screening device for CHV.