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The Secondhand Smoke Study is a medical research study investigating the physiologic, radiographic, and inflammatory responses of lungs to chronic exposure to secondhand tobacco smoke. Exposure to secondhand tobacco smoke (SHS) is associated with diverse health effects in nonsmokers. Although some of the toxic effects and underlying pathogenic mechanisms of acute exposure to SHS have been demonstrated through in vitro, animal, and controlled human exposure studies, the health effects of chronic exposure to SHS in humans have not been well established because of limitations with long term "natural" or manipulated SHS exposure experiments.
Over the past few years, we have recruited a cohort of flight attendants with history of "natural" chronic exposure to SHS to characterize its long-term health effects. Flight attendants (FA's) who worked on commercial aircraft before the ban on tobacco smoking (pre-ban FAs) had very high levels of occupational exposure to SHS over many years. Chemical analysis of post-flight urine samples from FAs in the pre-smoking ban era showed very high levels of urinary cotinine, the major metabolite of nicotine, in the range close to the levels currently observed in known "light" and in confirmed "experimental" smokers. This history of chronic high-intensity exposure, which better lends itself to quantification through employment history, makes the pre-ban FAs a unique population in which to study the long-term health effects of chronic exposure to SHS.
In previous study of pulmonary function tests (PFT) in the cohort, the investigators showed these never-smoking asymptomatic pre-ban FAs to have decreased flow at mid- and low-lung volumes and curvilinear flow-volume loops suggestive of mild airflow obstruction. More impressively, over half of the cohort had significantly reduced diffusing capacity (Dco) below the lower 95% prediction limit based on standard reference equations. Furthermore, in maximum effort (symptom-limited) cardiopulmonary exercise testing of this cohort, the investigators found that the pre-ban FAs with reduced Dco at rest had:
1. decreased exercise capacity (maximum workload and oxygen uptake) that was directly associated with the participants' forced expiratory volume in one second (FEV1):
2. reduced pulmonary capillary bed recruitment as indicated by lower exercise-induced increase in the participants' Dco and lower ratio of Dco to pulmonary blood flow with exercise; and
3. an inverse association between the participants' Dco during exercise and the years of exposure to SHS in the aircraft cabin in those FAs with over 10 years of pre-ban experience.
These findings are intriguing as they suggest lasting lung damage from remote but intense exposure to SHS in the aircraft cabin. Accordingly, the preliminary longitudinal data suggests that pre-ban FAs may have an accelerated decline in their lung function beyond what is expected from the aging process. Meanwhile, despite the progress in understating the mechanisms of SHS-induced lung damage, the health relevance of the observed respiratory abnormalities in this cohort remains unknown.
Allocation: Randomized, Endpoint Classification: Efficacy Study, Intervention Model: Crossover Assignment, Masking: Double Blind (Subject, Investigator)
VA Medical Center
University of California, San Francisco
Published on BioPortfolio: 2016-06-13T16:53:27-0400
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