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Intermittent noise stress causes baroreflex desensitization and decreased heart rate variability in Wistar Kyoto rats exposed to ozone
Citation:
Hazari, M., K. Philips, W. Oshiro, K. Stratford, M. Khan, L. Thompson, D. Herr, AND A. Farraj. Intermittent noise stress causes baroreflex desensitization and decreased heart rate variability in Wistar Kyoto rats exposed to ozone. Society of Toxicology 2018, San Antonio, Texas, March 11 - 14, 2018.
Impact/Purpose:
The purpose of this study was to determine the modifying effect of noise stress on the cardiopulmonary response to ozone. This work addresses the scientific questions related to the role of modifiable factors and air pollution.
Description:
This study shows that intermittent noise stress worsens the cardiopulmonary response of rats to ozone. It increases electrical disturbances and causes dysfunction the homeostatic regulation of the heart and vasculature. Although the acute cardiovascular health impacts of air pollution exposure are well established, the modifying effects of non-environmental factors on these responses still need to be characterized. This is important because a person’s physiology is not only determined by their current health (i.e. intrinsic state of the body), but also by the extrinsic factors (e.g. diet, social disruption, etc.) which alter bodily function, albeit subtly, and change subsequent responsiveness. Noise is encountered by millions of people every day and it can cause stress and other psychological disturbances. We previously showed that noise stress worsens arrhythmogenesis and cardiovascular dysfunction due ozone exposure. In this study we hypothesized that short-term exposure to noise would worsen cardiovascular response to ozone by altering homeostatic control mechanisms. Male Wistar-Kyoto rats were implanted with radiotelemeters for the measurement of heart rate (HR), blood pressure (BP) and electrocardiogram (ECG) and exposed to intermittent noise (85-90 dB) for one week after which they were exposed to either ozone (0.8 ppm) or filtered air for 4hrs. Heart rate and arterial pressure were used to calculate spontaneous baroreflex sensitivity (BRS) using the sequence method and heart rate variability was also determined. Although noise initially caused a typical stress response with high blood pressure, we noted that repeated exposures led to hypotension which suggests autonomic dysfunction. Exposure to noise caused BRS gain to decrease significantly and this response was shifted in the opposite direction by ozone. In addition, heart rate variability was significantly decreased during ozone in rats exposed to noise stress. Lastly, rats exposed to both noise and ozone experienced more episodes of sinoatrial node dysfunction than those that were not. These results suggest that intermittent noise stress alters the regulation of the cardiovascular system and renders it potentially susceptible to subsequent stressors, including air pollution. Therefore, non-environmental stressors like noise may be modifying the response to air pollution which can complicate characterization of its health effects. (This abstract does not reflect USEPA policy)