Breathing polluted air increases stress on the heart's regulation capacity, up to six hours after inhalation（吸入） of combustion¹-related small particles called PM2.5, according to Penn State College of Medicine researchers. Stress on the heart from exposure to high levels of PM2.5 may contribute to cardiovascular disease（冠心病） , said Duanping Liao, professor of public health sciences.

The body's ability to properly regulate heartbeat so the heart can pump the appropriate amounts of blood into the circulation system relies on the stability of the heart's electrical activity, called electrophysiology（电生理学） .

"Air pollution is associated with cardiopulmonary（心肺的） mortality（死亡率） and morbidity²（发病率） , and it is generally accepted that impaired³ heart electrophysiology is one of the underlying⁴ mechanisms," said Fan He, master's program graduate, Department of Public Health Sciences, Penn State College of Medicine. "This impairment（损伤） is exhibited through fluctuations⁵（变动，波动） in the heart rate from beat to beat over an established period of time, known as heart rate variability. It is also exhibited through a longer period for the electric activity to return to the baseline, known as ventricular（心室的，膨胀的） repolarization（极化恢复） .

"The time course, how long it would take from exposure to cardiac（心脏的） response, has not been systematically⁶ investigated," said He. "We conducted this study to investigate the relationship between particle matter and heart electrophysiology impairment, especially the time course."

The researchers published their results in recent issues of the Journal of Exposure Science and Environmental Epidemiology（流行病学） and in Environmental Health Prospective⁷.

Liao's team of researchers studied 106 people from central Pennsylvania, mostly in the Harrisburg metropolitan⁸ area（大都会区） . Nonsmokers over the age of 45 without severe cardiac（心脏的） problems wore air-quality and heart-rate monitors for 24 hours. The devices recorded data in one-minute intervals⁹（间隔） .

Results indicate that heart electrophysiology was affected¹⁰ up to six hours after elevated PM2.5 exposure. These adverse¹¹ effects may trigger the onset¹² of acute cardiac events and over time may result in increased risk of chronic¹³ heart disease.

PM2.5 refers to particles up to 2.5 micrometers in size. Their primary sources are diesel¹⁴ engine（柴油机） and coal combustion（燃烧） outdoors; and oil, gas or wood combustion for cooking and heating indoors. PM2.5 levels are regulated by the U.S. Environmental Protection Agency.

"Our findings may contribute to further understanding of the pathophysiology（病理生理学） of air pollution-related cardiac events, specifically our results indicating elevated PM2.5 exposure is associated with immediate¹⁵ disturbance¹⁶ of cardiac electrical activities within six hours after exposure," said Liao.