EFFECT OF INHALED RESIDUAL OIL FLY ASH ON THE ELECTROCARDIOGRAM OF DOGS

Abstract

Epidemiology studies have found associations between increases in air pollutants and increases in morbidity and mortality from cardiovascular disease. The 1995 finding by Godleski et al. at Harvard that inhalation exposures of dogs to high concentrations of residual oil fly ash (ROFA) caused changes in the ST segment and T waves in the electrocardiogram (ECG) suggested a potential mechanism, and also suggested that inhaled metals might contribute to the effect. Weconducted the present study to establish a baseline correspondence to the Godleski et al. findings in preparation for studies of the cardiac effects of specific particleborne metals. The ROFA used in this study consisted of 45% carbon and 15.5% transition metals by mass. In vitro assays using cultured A549 cells and rat alveolar macrophages demonstrated that the ROFA was biologically active but was not highly cytotoxic. Four 10.5-yr-old beagles were exposed by oral inhalation to 3 mg/m³ of aerosolized ROFA for 3 h/day on 3 consecutive days. During the exposures, ECGs were continuously recorded from leads I, II, III, and V₄. ECG data were also collected during three control exposures to clean air, during one of which changes were induced using drugs as a positive control. The ROFAexposures caused no consistent changes in the amplitude of the ST segment, the form or amplitude of the T wave, or arrhythmias. The data suggested a slight slowing of heart rate during exposure. Whether the difference between the present and previous findings resulted from differences in the composition of the two batches of ROFA or differences in methodology could not be determined by the study. This study did not address the cardiac effects of ROFAin subjects having preexisting cardiac susceptibility factors, nor was it a rigorous evaluation of effects on the frequency distribution of heart rate. Our results indicate that healthy dogs can inhale high concentrations of ROFA without changes in cardiac electrophysiology, which are detectable by clinical evaluations.