Air pollution could be putting patients with heart disease at risk by affecting blood vessels and clotting, researchers warn.
A study by the University of Edinburgh and Umeå University measured the effects of diesel exhaust on heart and blood vessel function in men who have previously experienced a heart attack.
The research, funded by the British Heart Foundation and published in the New England Journal of Medicine, found that inhalation of diesel exhaust caused changes in the heart's electrical activity, suggesting that air pollution reduces the amount of oxygen available to the heart during exercise.
Dr Nicholas Mills, of the University's Centre for Cardiovascular Sciences, said: "This study provides an explanation for why patients with heart disease are more likely to be admitted to hospital on days in which air pollution levels are increased. Most people tend to think of air pollution as having effects on the lungs but, as this study shows, it can also have a major impact on how our heart functions."
Twenty men who had suffered a previous heart attack were carefully screened to ensure they did not suffer from angina or heart rhythm problems and that their heart condition was stable and appropriately treated. The men were exposed for one hour to either filtered air or dilute diesel exhaust while intermittently riding a stationary bicycle in a carefully monitored exposure chamber in Umeå University. Heart function was monitored continuously and blood tests taken six hours after leaving the chamber.
Electrical monitoring of the heart showed that inhalation of diesel exhaust caused a three-fold increase in the stress of the heart during exercise. In addition, the body's ability to release a "guardian" protein known as t-PA (tissue plasminogen activator), which can prevent blood clots from forming, was also reduced by more than one third following exposure.
The link between air pollution and heart disease is strongest for the fine exhaust particles produced by road traffic. Researchers are particularly interested in diesel engines because they generate 10-100 times more pollutant particles than petrol engines. The number of diesel-powered automobiles is increasing in Europe and other parts of the world.
"Diesel exhaust consists of a complex mixture of particles and gases. Before we can recommend the widespread use of particle traps in diesel engines, we need to show that particles are the responsible component," Dr Mills said.
"If we do that, then it is likely that devices to filter particles from exhaust, will reduce exposure and benefit public health."
Professor Peter Weissberg, Medical Director of the British Heart Foundation (BHF), said: "There is already evidence that air pollution can make existing heart conditions worse. This research is helping us work out why. It shows that in patients with coronary heart disease, diesel exhaust can reduce the amount of oxygen available to the heart during exercise, which may increase the risk of a heart attack.
"Because of the overwhelming benefits of exercise on heart health, we would still encourage heart patients to exercise regularly, but preferably not when there is a lot of local traffic around. Heart patients can look out for pollution levels on their local weather forecasts."
Note to editors
- The British Heart Foundation (BHF) is the nation's heart charity, dedicated to saving lives through pioneering research, patient care, campaigning for change and by providing vital information. But we urgently need help. We rely on donations of time and money to continue our life-saving work. Because together we can beat heart disease. For more information visit bhf.org.uk