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Smoking silences critical pain messages.

Smoking silences critical pain messages

Cigarette smoking, already known as a heart-disease villain, may also blunt the perception of pain, preventing smokers from noticing potential warning signs of an impending injury. This new finding might help explain previous indications that smokers with coronary artery disease, compared with nonsmokers with similarly clogged arteries, appear less likely to experience chest pain during episodes of ischemia -- a reduction in blood flow to the heart that can lead to a sudden heart attack.

Scientists can't explain the smoking-related masking of pain, but animal studies hint that nicotine may block transmission of pain impulses.

Paula F. Miller and David S. Sheps at the University of North Carolina School of Medicine in Chapel Hill focused on 20 healthy men aged 19 to 44 who smoked an average of 23 cigarettes daily, and five nonsmoking men in the same age range. The researchers instructed volunteers not to smoke for 12 hours prior to the study's start. Then they applied a heat probe to each volunteer's forearm, letting the probe heat up gradually, and recorded the individual's pain threshold -- the temperature at which he first felt pain. Smokers and nonsmokers showed similar pain thresholds on this initial test.

Having gathered their baseline data, the investigators next instructed smoking volunteers to smoke three cigarettes of their usual brand, with a 10-minute wait after the first cigarette and a 30-minute wait after the second. Repeats of the heat probe test revealed that the smokers had become less sensitive to pain from the heat. On average, this group's "ouch" threshold rose from 44.9[degrees]C (112.8[degrees]F) before smoking to 45.5[degrees]C (113.9[degrees]F) after two or three cigarettes -- a small but statistically significant difference, says Miller, who described the results in Dallas last week at the American Heart Association's 63rd Scientific Sessions. The maximum pain the 20 men could tolerate increased after smoking, Miller notes, whereas non-smokers showed no change in pain threshold or tolerance.

While these findings suggest that healthy male smokers tolerate pain better than their nonsmoking counterparts, Sheps says further research must demonstrate this effect among male and female smokers with coronary artery disease. As for the pain-subduing mechanism underlying "silent" ischemia, he speculates that nicotine blunts pain messages by binding with nerve cells.

If studies confirm that suspicion, the implications may extend beyond silent ischemia. Nicotine's proposed pain-masking effect, says Sheps, may help explain why smokers have such a tough time kicking the habit.
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Author:Fackelmann, Kathy A.
Publication:Science News
Date:Nov 24, 1990
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