Small Healthy Side Effect of Smoking Discovered
Study finds heavy smokers who continue their habit after angioplasty do better
TUESDAY, May 25, 2004 (HealthDayNews) -- In a new and bizarre twist on the affects of smoking, researchers have found heavy smokers who continued to light up after undergoing angioplasty had a lower rate of recurring cardiovascular problems than their nonsmoking counterparts.
Before you decide to abandon several decades' worth of research demonstrating how smoking is, in fact, bad for you, consider that the smokers in need of this procedure were younger and had already suffered heart attacks and strokes.
"It is important to say that this was the only beneficial effect of smoking, because smokers had their disease at a younger age and had more myocardial infarction and stroke, so overall smoking was very harmful for our patients," emphasized study author Dr. Martin Schillinger, an associate professor of internal medicine at the University of Vienna Medical School in Austria. "Nevertheless, our observations suggest that carbon monoxide inhalation (without the bad side effects of smoking) may be worth being further investigated."
"In a paradoxical way, smoking may actually be helping or in some way protecting against restenosis [renarrowing of the arteries], but clearly the long-term effects of smoking are going to be deleterious," added Dr. Michael Dake, chief of cardiovascular and interventional radiology at Stanford University School of Medicine.
The study appears in the June issue of Radiology.
People with peripheral artery disease (PAD) have a narrowing or blockage in the arteries, which means that not enough oxygen gets to the arms or legs. Generally, the condition is treated with angioplasty, during which a physician inserts a small catheter through the blood vessel and threads it to the site of the obstruction, where it is inflated to prop open the vessel. Sometimes a stent, or wire-mesh cylinder, is left inside the artery to prevent it from closing up again.
However according to the study, up to 60 percent of the patients who have the procedure will experience restenosis, which is a natural response of the body to this kind of injury, and will have to go through the whole process again.
Scientists have been looking for ways to reduce the rates of restenosis.
Schillinger and his colleagues got the idea for this study from their previous work with an enzyme called heme oxygenase-1 (HO-1).
"HO-1 protects from restenosis after angioplasty most probably by the release of carbon monoxide," Schillinger explained. "In animal experiments, inhalation of carbon monoxide has been demonstrated to protect from restenosis. Smokers actually inhale carbon monoxide and have higher CO blood concentrations, so we speculated that this effect may be beneficial with respect to restenosis inhibition."
The researchers looked at 650 patients with PAD who had angioplasty (with or without stents) to open arteries leading to the legs. The patients were grouped according to their smoking status: nonsmokers; light smokers (one to nine cigarettes a day); habitual smokers (10 to 20 cigarettes daily); or heavy smokers (more than 20 cigarettes daily).
At the end of both six months and a year, the researchers found: heavy smokers had a 16 percent rate of renarrowing at six months and 29 percent at one year; those who smoked 10 to 20 cigarettes a day had rates of 20 percent and 35 percent, respectively; and for nonsmokers, the rates were 28 percent at six months and 54 percent at one year.
It's not the cigarettes per se but the carbon monoxide that appears to account for these results, the researchers said.
"Most probably it's the CO which exerts the protective effect," Schillinger said. Carbon monoxide is known to dilate blood vessels and also suppress the growth of smooth muscle cells in the wall of the artery.
These findings are not yet translatable into a treatment, the researchers cautioned.
"Unfortunately, as yet, systemic inhalation of pure CO is not practicable in these diseased patients, because it may cause severe hypoxia," Schillinger said.
Also, there are new treatments that already address this problem.
"We're getting more sophisticated. We have drug-coated stents. They're not systemic. They can be locally delivered and targeted to the actual site of the injury to control or manage the response," Dake said. "I don't know that you can take anything really useful [from this study], but it clearly shows that you can target restenotic processes through many ways. This one doesn't happen to be a particularly healthy way."
Nevertheless, Schillinger feels the subject of smoking and restenosis merits further research.
"We are now investigating whether CO donors (enzymes which produce CO in the vascular wall) may be applicable to the treated vessel segment," Schillinger said. "On the other hand, we are soon starting cautious CO inhalation in selected patients."
For now, the main message remains the same as the one the U.S. Surgeon General first delivered in 1964: Don't smoke.
"Nobody should start smoking after an intervention to reduce restenosis. Even if smoking is protective against restenosis at the treated segment, smoking will be very harmful for the rest of the vascular system, which was not treated by angioplasty," Schillinger said. "We are not recommending smoking to patients after angioplasty. However, these paradox findings may help us to develop strategies to use only the 'beneficial side effects of smoking.'"