Small airway dysfunction highly prevalent in China

Spirometry-defined small airway dysfunction is prevalent among adults in China, and cigarette smoking, air pollution exposure and higher BMI are preventable risk factors, according to a study published in The Lancet Respiratory Medicine.

“Our study shows that over 40% of Chinese adults aged 20 years and older had spirometry-defined small airway dysfunction, with cigarette smoking as a major preventable risk factor along with [fine particulate matter] exposure and increase of BMI,” Dan Xiao, MD, with the Tobacco Medicine and Tobacco Cessation Center and China-Japan Friendship Hospital, Beijing, and colleagues wrote.

Researchers with the China Pulmonary Health Study Group analyzed 50,479 participants (mean age, 49.3 years; 58% women) with valid lung function testing results from June 2012 to May 2015. Diagnosis of small airway dysfunction was defined as presence of two of the following three indicators of lung function less than 65% predicted: maximal mid-expiratory flow, forced expiratory flow 50% and forced expiratory flow 75%.

The prevalence of small airway dysfunction was 43.5% (95% CI, 40.7-46.3). Categorized further, 25.5% (95% CI, 23.6-27.5) had pre-small airway dysfunction, defined as normal FEV₁ and FEV₁/FVC ratio before bronchodilator inhalation, and 11.3% (95% CI, 10.3-12.5) had post-small airway dysfunction, defined as normal FEV₁ and FEV₁/FVC ratio before and after bronchodilator inhalation. The prevalence of small airway dysfunction was 51.2% among ever smokers, 45.1% among never smokers, 49.9% among current smokers and 56.5% among former smokers.

The researchers identified age, gender, urbanization, education, smoking, air pollution exposure, history of chronic cough, pneumonia or bronchitis in childhood, parental history of respiratory diseases and increased BMI as significant risk factors for small airway dysfunction, according to logistic regression analysis.

Among those with post-small airway dysfunction, the largest effect was observed in individuals who smoked and had air pollution exposure more than 50 g/m³ (adjusted OR = 1.45; 95% CI, 1.23-1.72) for the entire population and (aOR = 2.09; 95% CI, 1.38-3.16) for men. The researchers observed a dose-response association between cigarette smoking and post-small airway dysfunction among men, but not women.

Xiao and colleagues estimated that, in 2015, 426 million individuals in China had small airway dysfunction, 253 million had pre-small airway dysfunction and 111 million had post-small airway dysfunction.

“Our study further emphasizes the importance of implementation of comprehensive tobacco control for early lung care,” the researchers wrote. “Given that small airway dysfunction has been neglected as an important health issue globally, we call for global joint efforts on research, prevention, detection and management of the disease as a way of preventing early lung damage and injury.”