Abstract
BackgroundChronic bronchitis in patients with chronic obstructive pulmonary disease (COPD) is associated with poor respiratory health outcomes. However, controversy exists around whether non-obstructive chronic bronchitis (NOCB) is associated with airflow obstruction, lung function decline, and all-cause mortality in ever smoker or never smoker.Research QuestionThis systematic review and meta-analysis aimed to clarify the relationship between NOCB and incident COPD, lung function decline, and all-cause mortality, and to quantify the magnitude of these associations.Study Design and MethodsWe searched PubMed, Embase, and Web of Science for studies published up to October 1, 2021. Eligibility screening, data extraction, and quality assessment of the retrieved articles were conducted independently by two reviewers. Studies were included if they were original articles comparing incident COPD, lung function decline, and all-cause mortality in normal spirometry with and without chronic bronchitis. The primary outcomes were incident COPD and all-cause mortality. The secondary outcomes were respiratory disease-related mortality and lung function decline. Pooled effect sizes and 95% confidence intervals (CIs) were calculated using the random-effects model.ResultsWe identified 17,323 related references and included 14 articles. Compared with individuals without NOCB, individuals with NOCB had an increased risk of incident COPD (odds ratio: 1.98, 95% CI: 1.21–3.22, I2 = 76.3% and relative risk: 1.44, 95%CI: 1.13–1.85, I2 = 56.1%), all-cause mortality (hazard ratio [HR]: 1.38, 95%CI: 1.26–1.51, I2 = 29.4%), and respiratory disease-related mortality (HR: 1.88, 95%CI: 1.37–2.59, I2 = 0.0%). Data on the decline in lung function could not be quantitatively synthesized, but the five articles that assessed the rate of decline in lung function showed that lung function declines faster in individuals with NOCB. The mean difference in the additional decline in forced expiratory volume in 1 s ranged from 3.6 to 23.2 mL/year.InterpretationIndividuals with NOCB are at a higher risk of incident COPD and all-cause mortality than individuals without NOCB, highlighting the crucial need for strategies to screen for and reduce NOCB risk.Systematic Review Registrationhttps://www.crd.york.ac.uk/PROSPERO/ PROSPERO, identifier CRD42020202837
Highlights
Chronic obstructive pulmonary disease (COPD) is a common, preventable, and treatable disease that is characterized by persistent respiratory symptoms and airflow obstruction
The data from both articles were included in this study because we did not combine higher allcause mortality (HR) and odds ratio (OR) data; rather, we presented the corresponding results separately
The main finding from our systematic review and meta-analysis is that individuals with non-obstructive chronic bronchitis (NOCB) experience a moderately elevated risk of incident COPD, all-cause mortality, and respiratory disease-related mortality, as well as faster lung function decline
Summary
Chronic obstructive pulmonary disease (COPD) is a common, preventable, and treatable disease that is characterized by persistent respiratory symptoms and airflow obstruction. In 2001, the Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease (GOLD) report proposed an “at risk” stage (GOLD stage 0), which was defined by the presence of symptoms (chronic cough and sputum production) in the absence of spirometry abnormalities that cross the diagnostic threshold for COPD [12]. This category was later abandoned in GOLD 2006 because not all of these individuals progressed to COPD [13]. Research Question: This systematic review and meta-analysis aimed to clarify the relationship between NOCB and incident COPD, lung function decline, and all-cause mortality, and to quantify the magnitude of these associations
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