Heart rate variability among gas station attendants exposed to benzene, toluene, and xylenes (BTX) in Sri Lanka

Abstract

Introduction: Benzene, toluene, and xylenes (BTX) exposure among gas station attendants in Sri Lanka is high. Cardiovascular morbidity and mortality are reported to be higher among those exposed to BTX. A hypothesis is based on alterations in the autonomic nervous system, especially disruption of autonomic regulation of the heart. Autonomic regulation of cardiac functions can be assessed by short-term heart rate variability (HRV), which measures the fluctuations in the interval between sequential sinus heartbeats. Objective: To determine whether BTX exposure affects the heart rate variability (HRV) among gas station attendants. Methods: Forty-nine gas station attendants from the Gampaha district of Sri Lanka, aged between 19 and 65 years, were recruited for the study. Age and gender-matched controls (n = 46) without occupational exposure to fuel were used as controls. Ethical approval for the study was granted by the Ethics Review Committee of the Faculty of Medicine, University of Kelaniya, Sri Lanka. Informed written consent was obtained from each participant. Demographic data were collected, and a physical examination was performed before the HRV assessment. We measured SDNN, RMSSD, pNN50, HF, LF, and LF: HF ratio as HRV indices. Pre- and post-shift samples of end-exhaled air were collected and analyzed for BTX using a thermal desorption gas chromatography–mass spectrometry system (TD-GC-MS) among 24 gas station attendants and 14 controls. As a proxy of shift exposure, we calculated the increase from pre-shift (as a baseline) to postshift and reported this as ‘delta’. Results and discussion: For gas station attendants (n = 24) median pre-/post-shift exhaled air concentrations (ng/L) were: benzene 10.47/ 19.00; toluene 10.41/21.86; m/p-xylene 1.63/2.14; o-xylene 0.93/1.42. For controls (n = 14) these values were 9.40/11.05, 3.19/3.91, 1.23/ 1.43 and 0.47/0.47. The heart rate variability (HRV) analysis showed significantly higher SDNN and SD2 among the gas station attendants (n = 49) than controls (n = 46) (Mann Whitney U = 842.00, p = 0.034 and Mann Whitney U = 843.50, p = 0.035, respectively). RMSSD, pNN50, Total power, HF, and SD1 among gas station attendants negatively correlated at a significant level with the mean increment in exposure to BTX (p\0.05).Conclusions: Exposure to BTX alters the HRV indices, indicating an effect on autonomic cardiac regulation. Funding: University of Kelaniya research grant: RP/03/04/03/01/ 2017, Foreign Award 2017 of the Dutch Occupational Hygiene Society (NVvA).