Prevalence and characteristics of dysfunctional breathing in patients with asthma in the Japanese population

Background: Dysfunctional breathing (DB) is a major asthma comorbidity; however, it is not well recognized in Japan. Moreover, it has rarely been reported in the asthma population, and its clinical characteristics are unclear. We aimed to clarify the clinical characteristics of DB as a comorbidity in patients with asthma in Japan. Questionnaire surveys were conducted among patients with asthma at medical facilities in three regions of Japan (Niigata, Kumamoto, and Tokyo). Methods: This cross-sectional questionnaire survey targeting patients with asthma who had regularly visited medical institutions and their doctors was conducted from September to November 2021. The questionnaire addressed the control status and method of treatment. The diagnosis of DB was evaluated using the Nijmegen questionnaire (NQ). Results: There were 2087 eligible participants. Based on their NQ scores, 217 patients were classified into the DB group (NQ >= 19). There were significant differences with respect to sex, disease duration, Asthma Control Test (ACT) scores, Patient Health Questionnaire-9 (PHQ-9) scores, type-2 biomarkers, pulmonary function indices, treatment methods, severity, and asthma exacerbations in the previous year between the DB and non-DB groups. In the multivariate analysis, there were significant differences in sex, disease duration (>= 15 y), ACT scores (<20), and PHQ-9 scores (>= 10). The cluster analysis of cases with DB classified the population into four clusters. Conclusions: The asthma population with DB exhibited several characteristics, including depression and poorly controlled asthma. Further large-scale interventional investigations with longer follow-up periods are necessary to verify these findings.