A new Scottish and Swedish study suggests that exposure to diesel fumes could put heart disease patients at risk from reduced blood supply to the heart and clots.
The research is published in the New England Journal of Medicine, was funded by the British Heart Foundation (BHF) and is the work of scientists at Edinburgh University in Scotland and Umeå University in Sweden.
The researchers examined how diesel exhaust fumes affected the heart and blood vessels of men who had recovered from a heart attack and were stable.
They found that inhaling diesel fumes while exercising changes the electrical behaviour of the heart, implying that air pollution reduces the amount of oxygen reaching the heart during exercise.
Lead author, Dr Nicholas Mills of Edinburgh University’s Centre for Cardiovascular Sciences said in a prepared statement that:
“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,” he explained.
The scientists enrolled 20 men who were around 60 years old who had experienced a heart attack. They screened them to make sure they were stable and appropriately treated to prevent a further heart attack and not showing signs of angina or having heart rhythm problems and had good tolerance for exercise.
The men took it in turns to exercise on a stationary bicycle inside a carefully monitored exposure chamber where they were exposed, on two separate visits, to filtered air and diluted diesel fumes (about the same as being in heavy traffic). They exercised for an hour, with rest breaks every 15 minutes, still inside the chamber.
The men had electrodes attached to them all the time they were in the chamber to monitor their hearts and they gave blood samples six hours after leaving it. The air pollution in the chamber was also carefully measured.
The results showed that while they were inhaling diesel fumes the men experienced a three fold increase in stress on the heart.
Also, their body’s ability to release t-PA, the guardian protein that protects against blood clots, was down by one third after being exposed to diesel fumes. t-PA is short for tissue plasminogen activator.
The researchers concluded that:
“Brief exposure to dilute diesel exhaust promotes myocardial ischemia [reduces blood supply to the heart] and inhibits endogenous fibrinolytic capacity [clot busting] in men with stable coronary heart disease.”
They said that:
“Our findings point to ischemic and thrombotic mechanisms that may explain in part the observation that exposure to combustion-derived air pollution is associated with adverse cardiovascular events.”
Other studies have linked the fine particles in air pollution, and from road traffic fumes in particular, to heart problems.
Diesel engines generate between 10 and 100 times more fine particles than petrol engines and their numbers are rising throughout the world.
Mills touched on the importance of getting the research right, and establishing that it is the particles and not for example the chemicals that are mainly responsible for the deterioration in heart performance, before going ahead and recommending modifications to car design:
“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.”
“If we do that, then it is likely that devices to filter particles from exhaust, will reduce exposure and benefit public health,” he added.
Medical Director of the BHF, Professor Peter Weissberg, 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.”
However, he did not recommend that people stop exercising because of fear of what air pollution might do their heart. The benefits outweigh the risks, especially if you avoid exercising near traffic during the rush hour:
“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,” explained Weissberg.
“Ischemic and Thrombotic Effects of Dilute Diesel-Exhaust Inhalation in Men with Coronary Heart Disease.”
Mills, Nicholas L., Tornqvist, Hakan, Gonzalez, Manuel C., Vink, Elen, Robinson, Simon D., Soderberg, Stefan, Boon, Nicholas A., Donaldson, Ken, Sandstrom, Thomas, Blomberg, Anders, Newby, David E.
N Engl J Med 2007 357: 1075-1082
Volume 357:1075-1082; September 13, 2007; Number 11.
Written by: Catharine Paddock