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Pulmonary Function Changes on Exposure To Air Pollutants: Inferences From Systematic Review and Meta-Analysis of Observational Studies Involving Traffic Regulators

Introduction: Air pollution poses a considerable threat to health across the world by increasing the risk for multiple systemic ailments including that of respiratory ailments. We systematically reviewed the literature and quantified the pulmonary dysfunction through evidence synthesis of comparison between individuals with high exposure to air pollutants, i.e., such as traffic regulators and relatively unexposed comparators. 
 
Methods: Observational studies that reported the pulmonary function test comparison results between air pollution exposed traffic regulators and healthy matched controls were systematically searched in PubMed, Scopus and EMBASE databases since inception to June 2020. The PRISMA guidelines were adhered during study selection, data extraction. The mean difference in forced expiratory volume during the initial first second (FEV1), forced vital capacity (FVC), the ratio of FEV1 and FVC, peak expiratory flow rate (PEFR), and forced expiratory flow between the two extreme quartiles (FEF25%-75%) were pooled using a random-effect model. Heterogeneity was assessed using Cochran-Q test and I2 statistic. Risk of bias was assessed using the risk of bias in non-randomized studies of exposures (ROBINS-E). Sub-group analyses and meta-regression analyses were performed. 
 
Results: Nineteen studies including 1922 traffic regulators and 1384 control individuals were included in the quantitative synthesis. The pooled mean difference of FEV1, FVC, FEV1/FVC, PEFR and FEF25% - 75% were -0.49L (-0.71 to -0.28; n=18, I2=96.49), -0.33L (-0.59 to -0.07; n=15, I2=96.65), -3.19 % (-6.68 to 0.29; n=12, I2=95.38), -0.89 L/sec (-1.65 to -0.12; n=13, I2=98.12) and -0.6L (-0.96 to -0.23; n=6, I2=94.06) respectively. On risk of bias assessment among the included studies were mainly scored as moderate (15, 27) to severe on ROBBINS-E. Assuming a cumulative exposure of 5 years as reported in majority of the studies, the estimated reduction in FEV1 & FVC were approximately 100ml/year and 70ml/year respectively in the exposed population. 
 
Discussion: We observed the pulmonary function derangements associated with exposure to air pollution. However, considering high heterogeneity and low quality of primary evidence, further high quality longitudinal studies with quantification of over the time decline could be of immense value in understanding the functional decline. Present observations should caution the policymakers towards drafting regulations for reducing air pollution and the need for preventing steps for reducing the exposure.