By Ben Harder
If being stuck in traffic seems to elevate your blood pressure, the stress of driving could be only partly to blame. In a laboratory setting, volunteers breathing pollutants generated by sources such as vehicle engines experience slight but steady increases in blood pressure, researchers report.
The effect disappears quickly when exposure ends, at least in healthy people, Bruce Urch of the University of Toronto and his fellow investigators say. But researchers call the newly observed effect consistent with past findings that link acute cardiovascular problems, including fatal heart attacks, to short-term contact with airborne particles.
Urch and his group asked 23 healthy volunteers, age 19 to 50, to sit inside a small, sealed chamber and to breathe through a mask on two or three separate occasions. During each 2-hour trial, the investigators piped into the mask either filtered air or air containing about 150 micrograms of particles per cubic meter (µg/m3) and about 121 ozone molecules per billion air molecules. Each volunteer experienced each treatment at least once, without knowing which was which.
The researchers maintained the 150 µg/m3 level by concentrating particles from air outside the research facility in Toronto. That density of particles is typical of that in some heavily polluted cities and might be found elsewhere under certain circumstances, for example, in a traffic jam inside a tunnel, Urch says. The ozone was generated inside the facility by sparking the air with electricity.
During exposure to polluted air, volunteers’ diastolic blood pressure, or low-pressure number, rose an average of about 6 millimeters of pressure, or 9 percent, Urch and his colleagues found. Breathing filtered air for 2 hours had no effect on blood pressure. The scientists report their findings in the August Environmental Health Perspectives.
The investigators analyzed variations in the chemical constituents of the particulate matter inhaled by different volunteers. The results suggest that organic particles or unidentified compounds associated with them have the strongest effect on blood pressure.
The study provides a “live recording” of people’s blood pressure rising in response to exposure to realistic concentrations of airborne particles, says microvascular physiologist Timothy R. Nurkiewicz of West Virginia University in Morgantown. That effect had been suspected on the basis of prior findings, he says.
The increase in blood pressure is “very subtle,” Nurkiewicz notes. Prior studies, including one by the Toronto group, suggest that the pressure rise doesn’t last more than a few minutes once exposure ends. All the same, Nurkiewicz says, in people who are older or have poorer cardiovascular health than the study volunteers did, small and transient changes can have serious cardiovascular consequences.
Epidemiologist Nino Künzli of the University of Southern California in Los Angeles agrees. “A blood pressure shift of a few millimeters in a single person is unlikely to cause immediate harm,” he says. “But a small shift of the population average value means in essence that some people get pushed into levels of immediate clinical risk.”
