Objective Although it has been well defined that long-term exposure to secondhand smoke (SHS) is associated with cardiovascular mortality, the acute cardiovascular effects of SHS exposure are still being explored. The aim of this study was to examine cardiovascular autonomic response, as measured by heart rate variability (HRV), to short-term SHS exposure among boilermaker construction workers.
Methods Boilermakers were recruited from a local apprentice hall where they were monitored while exposed to SHS for approximately 6 hours. A repeated measures study design was used where resting 5-lead ECGs were taken from individuals before SHS exposure (baseline), following SHS exposure (post) and the morning following SHS exposure (next-morning). The ECG recording was analysed in time (SDNN, rMSSD) and frequency (LF, HF) domain parameters in 5-minute averages. Personal SHS exposure was monitored through SidepakTM Aerosol Monitor and quantified by fine particulate matter (PM2.5). Separate linear mixed-effects regression models were used to compare post- or next-morning after controlling for baseline. Exposure-response relationships with PM2.5 were examined.
Results 52 male boilermakers, including 30 non-smokers, were monitored between June 2010 and June 2012. The mean SHS exposure was 167 ug/m3. After SHS exposure post 5-minute SDNN, rMSSD, LF and HF were significantly (p < 0.05) lower than before SHS exposure. We observed significant (p < 0.05) differences in SDNN, rMSSD, LF and HF between smoker and non-smokers. However, this effect had no linear dose-response relationship with PM2.5. The next morning SDNN, rMSSD, LF and HF were also significantly (p < 0.05) lower than the baseline, but no linear dose-response with PM2.5 was observed.
Conclusion We observed a change in HRV both immediately and the next morning following SHS exposure. However, results indicated that there was no linear dose-response relationship between PM2.5 and HRV. It is unclear whether SHS-derived PM2.5 or other factors contributed to the altered cardiovascular autonomic response.