Impact of Airflow Obstruction on Long-term Mortality in Patients with Asthma in Japan

Background: The long-term prognosis of asthma with airflow obstruction is poorly understood in Japan. The aim of this retrospective 26-year study was to investigate the long-term mortality risk of airflow obstruction in asthmatics.

Methods: Using data from the Omuta City Air Pollution-related Health Damage Cohort Program, mortality risk ratios of airflow obstruction in Japanese Individuals were analyzed by Cox proportional hazards models. Airflow obstruction was considered to be present when the forced expiratory volume in 1 sec (FEV)/forced vital capacity ratio was <0.7 and FEV predicted was <80% based on spirometry.

Results: Among the 3146 victims with chronic respiratory diseases, 697 with adult asthma were selected. Median follow-up period was 26.3 (range 0.9-40.9) years. The airflow obstruction group (n = 193) showed significantly higher rates of mortality related to respiratory problems (risk ratio [95% confidence interval] 1.51 [1.86-1.93], P = 0.0017) and asthma attacks (1.86 [1.30-2.66], P = 0.0011) than the without airflow obstruction group (n = 504). Airflow obstruction was an independent risk factor for both respiratory-related (1.84 [1.36-2.49], P = 0.0001) and all-cause (1.44 [1.17-1.76], P = 0.0008) mortality after adjustment for age, sex, body mass index, and smoking status. More severe airflow obstruction was significantly associated with poorer prognosis.

Conclusions: This long-term cohort program revealed the impacts of asthma with airflow obstruction as an independent mortality risk. Findings suggest that intervention and prevention of airflow obstruction can reduce long-term mortality in patients with asthma.