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Treadmill stress test after diesel exhaust particulate exposure reveals a time-dependent shift from parasympathetic to sympathetic dominance
Citation:
Carll, A. P., C. Perez, D. P. Costa, AND A. FARRAJ. Treadmill stress test after diesel exhaust particulate exposure reveals a time-dependent shift from parasympathetic to sympathetic dominance. Presented at Society of Toxicology (SOT) Annual Meeting, San Francisco, CA, March 11 - 15, 2012.
Impact/Purpose:
We demonstrate that diesel exhaust particulate exposure induces autonomic imbalance characterized by early parasympathetic dominance followed by a later increase in sympathetic tone, which collectively may increase risk for adverse cardiovascular events. Moreover, the treadmill stress test is useful in unmasking the latent cardiovascular effects of air pollutant exposure
Description:
Epidemiological studies suggest that particulate matter (PM) air pollution is a major trigger of acute cardiac events-including arrhythmia-especially in those with preexisting cardiac disease. Diesel exhaust (DE) contributes the majority of urban fine and ultrafine PM, and is thus likely a key trigger of acute cardiac events. Research suggests that several interrelated mechanisms underlie the acute cardiotoxicity of PM, including autonomic nervous system imbalance. Abnormal heart rate (HR) and HR variability (HRV) responses to treadmill challenge are indicative of autonomic dysfunction and predictive of cardiovascular mortality. We hypothesized that a single intra-tracheal instillation (IT) of DE particles (DEP, 500 ug/kg) in hypertensive heart failure-prone rats would provoke abnormal HR and HRV responses to treadmill. Rats were monitored by radiotelemetry during treadmill challenge at 24-h pre-IT and 3-and 24-h post-IT. Relative to saline-instilled rats, DEP significantly decreased HR and low-to high frequency ratio of HRV (LF/HF) while increasing time domain HRV parameters (SDNN & RMSSD) during treadmill deceleration and recovery at 3 h post-IT, suggesting parasympathetic dominance. Upon 24-h post-IT treadmill challenge, DEP significantly increased HR while decreasing SDNN and RMSSD during acceleration, indicating sympathetic dominance relative to saline. DEP did not affect arrhythmia counts immediately before, during, or after treadmill exercise. Thus, DEP exposure induced autonomic imbalance characterized by early parasympathetic dominance followed by a later increase in sympathetic tone, which collectively may increase risk for adverse cardiovascular events. Moreover, the treadmill stress test is useful in unmasking the latent cardiovascular effects of air pollutant exposure. (Abstract does not reflect EPA policy; Supported by UNC/EPA CR83323601.)