How does nitroglycerin stop heart attacks?

April 30, 2004

Dear Cecil:

Recently a friend of the family had a heart attack. While he was in the hospital, they gave him nitroglycerin pills to stop the attack and ease his chest pains! I consider myself as having a rational mind, but the ingestion of explosives (no matter how small the amount) does not on the surface seem to be a great way to promote cardiovascular health! In fact, it would seem that nitro might have caused a few heart attacks (especially around the Fourth of July). How does nitroglycerin stop heart attacks?

People nowadays are such wimps. If you're looking for strong medicine, how can you do better than a high explosive? The nitroglycerin in the pills, patches, and sprays that heart patients use for angina (chest pain) is in fact the same stuff you find in dynamite--the residue the drug leaves on patients' skin and clothing is often enough to set off airport bomb-sniffing machines. The medicinal dose is tiny and diluted with inert material, so it's completely nonexplosive; even so, nitroglycerin is one medicine I'd hesitate to shake before use.

I'm kidding, of course. Still, straight nitroglycerin (an oily yellow liquid) isn't something you'd want to take a swig of--even if we ignore the fact that it's poisonous, the merest jolt will detonate it. The man who discovered it in 1846, Italian chemist Ascanio Sobrero, had his face scarred by a laboratory explosion. The Swedish inventor of dynamite, Alfred Nobel, made his pile after figuring out in the 1860s that mixing nitro with diatomaceous earth would produce a relatively stable explosive paste that was much safer to use.

Laborers in Nobel's factories were the first to feel nitroglycerin's therapeutic effects. When they arrived at work each morning, those with heart problems found that their chest pains subsided (though almost everybody on the job noticed that sometimes their heads hurt like hell). Turned out the nitroglycerin vapor in the factory air was acting as a vasodilator, increasing blood flow both to the heart (which needed it, at least in the case of the angina sufferers) and to the head (which didn't).

Nitroglycerin pills have been a standard treatment for angina and heart attack symptoms since 1879--doctors prescribed them for Nobel himself not long before his death in 1896 (he refused to take them--couldn't brook the headaches). But more than a century passed before scientists understood how they worked. In the 1970s, researchers established that the body converts nitroglycerin into nitric oxide, and in the '80s they demonstrated that nitric oxide is a messenger molecule that tells the smooth muscles surrounding blood vessels to relax. (A heart attack basically means that not enough blood is reaching your cardiac muscles.) In 1998 three scientists who'd been instrumental in unlocking the mystery of nitroglycerin were collectively awarded--I'm telling you, this story has irony out the wazoo--the Nobel Prize in medicine.

While I've got your attention, we need to discuss a related matter. Maybe you're thinking you know another use for nitroglycerin--in the "nitro-burning" funny cars at drag races. (You know, the ones they have on Sunday, Sunday, Sunday!) Sorry, but no--drag racers aren't that crazy, though they're still pretty crazy, as we shall see. The fuel in question is nitromethane. This nitro compound provides extra horsepower, although it contains less energy than gasoline on a per-pound basis. Unlike gasoline, nitromethane has some oxygen built into its molecular structure, meaning the engine doesn't have to draw in as much air to support combustion--the ratio of air to fuel vapor in a conventionally powered engine is 15:1, compared to 1.7:1 if you're burning nitromethane. Less air = more room for fuel in the cylinder head = more power. Lots more power. Provided your engine can handle the extra load, you can get two or three times the horsepower from your beater by changing to nitro.

Unfortunately, nitromethane, like nitroglycerin, has a few practical drawbacks. One is that combustion is seldom complete before the hot gases are pushed out of the engine, meaning that dragsters typically spit fire from their exhaust pipes. (One recognizes that many aficionados of the sport don't consider this a drawback.) Another is that nitro can be tricky to handle. Though it's not very volatile (at room temperature, a match dropped in it will go out), I understand that if you smack a hammer into a puddle of nitro on the garage floor, well, you da bomb--or, perhaps more accurately, you da shrapnel. I'll spare you the chemistry, and won't even take points off if you get your methane mixed up with your glycerin, provided you take home the essential point, namely that if you've got nitro in there somewhere, it's not going to be a dull day.

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