UC Irvine

Abstract

Effects of Ambient Particulate Matter 2.5 (PM2.5)Exposure on Average Heart Rates and Mean Blood Pressures of Spontaneously Hypertensive Rats By Michael H. Vo Master of Science In Environmental Health Sciences Associate Professor Andrea De Vizcaya Ruiz, Chair.

Air pollution is a major health risk. Chronic exposure to particulate matter (PM) has been associated with increased risks for several cardiovascular (CV) diseases. Exposure to fine particulate matter (aerodynamic diameter ≤ 2.5 μm; PM2.5) is causally related to increases in sudden cardiac death, strokes, and myocardial infarction, which are coupled with erratic heart rates and blood pressure changes. The aim of this study is to assess changes in average heart rate (HR) and mean blood pressure (BP) in spontaneously hypertensive rats (SHRs) after 11-week exposure to ambient PM2.5. Six male SHRs were exposed 5 hours per day, 4 days per week (Mon-Thurs) for 11 weeks (June 10, 2008 to August 21, 2008) to concentrated ambient PM2.5 (133 +/- 20 mcg/m3). Six control male SHRs were simultaneously exposed to filtered, purified air for the same periods. Study rats were implanted with telemetry devices (DSI, model number C50-PXT) which recorded electrocardiograms (ECGs), heart rates (HR) and blood pressure (BP). Data were acquired continuously in 5-minute increments, transmitted, stored and analyzed using DataQuest Art ® software. Mixed-effects ANOVA was used to test for the interaction between four groups (Control-Day, Exposed-Day, Control-Night, and Exposed-Night) and the respective changes in blood pressure and heart rate month-to-month and from the beginning to the end of the study. Marginal means with 95% confidence intervals were reported and interpreted for each analysis. Bivariate analyses were performed if a significant main effect was detected for an interaction. Statistical significance was assumed at an alpha value of 0.05, and all analyses were performed using SPSS Version 29 (Armonk, NY: IBM Corp.) There was a statistically significant reduction (22%) in average heart rates and a statistically significant increase (19%) in mean blood pressures of PM2.5 exposed rats over the course of 11 weeks compared to Air-exposed rats. . Possible explanations for the reduction of the average heart rates include the highly responsive parasympathetic nervous system of the exposed rats, which mitigates the elevation of blood pressure caused by activation of the sympathetic nervous system and possible development of an adaptation response by exposed rats to repeated PM2.5 exposure by strengthening the parasympathetic nervous system, hence leading to continuous reduction of average heart rates. In summary, following repeated PM2.5 exposure, there was a statistically significant reduction in average heart rates and a statistically significant increase in mean blood pressures of PM2.5 exposed rats. The reduction of the average HR of exposed rats appears to compensate for the increase in the mean BP to allow the rat to maintain a state of homeostasis. With prolonged PM2.5 exposure, the elevation of blood pressure continues to compensate for further reduction of heart rate. The relentless increase in blood pressure leads to accelerated hypertension and, ultimately, death due to myocardial infarction, arrhythmia, and cardiac failure. Funding: The study was funded in part by the U.S. EPA Grant Number RD-83195201. In addition, "this study was supported by the Occupational Medicine Residency Program of the Southern California NIOSH Education and Research Center (SCERC), Grant Agreement Number T42 OH008412 from the Centers for Disease Control and Prevention (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the CDC.”