The presence of a higher residual volume-to-total lung capacity ratio (RV/TLC) in individuals with preserved spirometry, but at risk for obstruction because of secondhand smoke, may be indicative of increased respiratory symptoms and lower exercise capacity, according to an article published in BMJ Open Respiratory Research.
Researchers conducted an observational cross-sectional analysis of data from US airline flight crewmembers (256 included; 179 underwent cardiopulmonary exercise testing) from July 2007 to July 2015 who were exposed to secondhand smoke in the cabin environment before the smoking ban on US commercial aircraft. The purpose of the study was to measure the RV/TLC in this cohort of flight crewmembers to evaluate the clinical significance of lung volumes representing air trapping. It was hypothesized that the presence of lung volumes reflecting air trapping in individuals with preserved spirometry at a high risk for chronic obstructive pulmonary disease (COPD) as a result of exposure to secondhand smoke could be a phenotype of individuals with greater respiratory symptoms and lower capacity for exercise.
Of the 50.4% participants who reported respiratory complaints, 44.5% reported ≥2 episodes of cough per year. There was a statistically significant association between the likelihood of having any of the respiratory symptoms with a higher RV/TLC, with an average 9% increase in odds ratio for each 1% increase in RV/TLC (n=256; P =.011). In addition, higher RV/TLC was associated with a lower VO2max, whereas percentage of expiratory flow limitation was also noted to have a negative association with VO2max (n=32; r2=0.40; P =.017).
Furthermore, RV/TLC was a more accurate predictor than forced expiratory volume in 1 second (FEV1) and FEV1/forced vital capacity (FVC) in discriminating between individuals with and without reported respiratory symptoms; however, the results were not statistically significant on receiver operating characteristic analysis. Area under the curve measurements for RV/TLC, FEV1, and FEV1/FVC were 0.60, 0.55, and 0.46, respectively. Therefore, individuals were 49% less likely to achieve their maximum predicted exercise capacity with RV/TLC values ≥90%, with a VO2max of 100% predicted or higher (P =.045).
Researchers found participants exposed to secondhand smoke had an inverse association with maximum work level achieved, with a decrease of 7±4 mL/min in VO2max and 0.8±0.4 W in Wattsmax achieved with each year of exposure to secondhand smoke in cabins (P =.040 and P =.027, respectively).
It was concluded that there was a remarkable variability in FEV1/FEV or FEV1 in crewmembers exposed to secondhand smoke in aircraft cabins, suggesting that the inclusion of RV/TLC adds another dimension to COPD not routinely captured by standard airflow indices that could potentially be predictive of lower maximum exercise capacity and greater odds of reporting respiratory symptoms. Clinicians should be aware of this subtle variation that could potentially be used as prognostic criteria in the near future for individuals with preserved spirometry at risk for COPD secondary to any cause.
Arjomandi M, Zheng S, Geerts J, et al. Lung volumes identify an at-risk group in person with prolonged secondhand tobacco smoke exposure but without overt airflow obstruction. BMJ Open Respir Res. 2018;5(1):e000284.