Can air pollution affect heart health?

­Our bodies can't run with­out oxygen. All of our cells need it, and they rely on our lungs and heart to deliver it.

Every breath we take brings oxygen into our lungs, and the lungs are the first destination for the blood pumped out by the heart. When the right atrium contracts, it squeezes blood into the lungs so it can pick up oxygen from the air there. That oxygenated blood then enters the left atrium, which sends it out to the rest of the body.

But what happens when there's carbon monoxide, particulates or sulfur oxides in our lungs right alongside the oxygen? The blood picks up that stuff, too, and it gets to the blood supply, the heart and to every inch of our bodies.

That's the problem: It's all connected. Unfortunately, the heart reacts just as badly to air pollution as our lungs do. While the main causes of heart disease are poor diet, family history, obesity, diabetes and smoking, there's increasing evidence that heart problems are significantly impacted by pollution. For instance, carbon monoxide from secondhand smoke decreases the amount of oxygen our blood can carry, which can starve the heart muscle of the oxygen it needs to work properly. Particulates in diesel exhaust can cause blood vessels to constrict, limiting blood flow.

These particulates appear to be especially damaging in terms of heart health.

Particulates are tiny bits of liquid or solid matter. When we talk about this type of air pollution harming the heart, we're usually talking about PM2.5 -- particulate matter that's less than 2.5 micrometers in diameter. That's roughly 1/10,000th of an inch, or about one-tenth the diameter of a human hair. These particles are small enough to get deep into the lungs. The American Heart Association reports a 1.4 percent increase in heart-related deaths for each 10 micrograms of particulates per cubic foot of air [source: AHA]. And 10 micrograms is not a lot. The U.S. Environmental Protection Agency (EPA) considers the low concentration of 35.5 micrograms (average over the course of 24 hours) to be acceptable for health purposes [source: GADNR].

­Some researchers have found that even those EPA-approved levels can cause damage to the heart and blood vessels, though, especially in people already suffering from heart disease. And now they might know why.

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­A recent study, published in 20­08, found a reason why hearts seem to react so badly to air pollution: Particulate matter can interfere with the heart's electrical system [source: Science Daily].

The heart muscle pumps blood by contracting, squeezing the blood within its arteries to force it into the rest of the body. Just like any other muscle, the heart's contraction is triggered by an electrical impulse. In the heart, the impulse is generated by the SA node attached to the right atrium. The rate and rhythm of this impulse determines the heart beat, or pulse (see What determines the rhythm of your heart? to learn more).

Harvard University scientists studied 48 heart patients after they left the hospital, and tested their heart function after having been exposed to Boston air after weeks and then months. What they found was a change in heart conductivity, called ST-segment depression. ST-segment depression is essentially a reduction in the heart's ability to conduct electricity.

Not only particulates but also black carbon, a general term describing traffic exhaust, was found to correlate with ST-segment depression. When levels of black carbon and particulates in the air increased, there was an increase in ST-segment depression among the test subjects.

What does this mean for those of us breathing polluted air?

The short of it seems to be that an already damaged heart is more susceptible to the effects. In people with atherosclerosis (clogged arteries), air pollution has actually been shown to speed the rate at which plaque builds up on artery walls. Still, while people with healthy hearts are less at risk for cardiovascular trauma related to air pollution, we all feel the effects. The AHA estimates that, on average, we could all be losing one to three years of life expectancy due to pollution-related heart issues [source: AHA].

The good news is, we can still do something to stay healthy while the world's governments slowly get around to fixing the air-pollution problem. We can all try to follow the guidelines given to heart patients: avoid heavy traffic when possible, stay indoors on the worst air-quality days, and, of course, get the heck out of L.A.

­For more information on air pollution, heart health and related topics, look over the links on the next page.

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