Walk-through electronic detection systems pose no hazard to people with implanted heart devices under normal conditions, a new study reports.

Nonetheless, because of the slight possibility of interference from prolonged exposure, experts cautioned patients with such devices not to linger more than 15 seconds--a very slow walking pace--within anti-theft or airport security machines.

"More intense exposure in both time and proximity may lead to inappropriate shocks," the study warned.

An estimated 400,000 people worldwide carry implantable cardioverter-defibrillators (ICDs) in their chests. The devices are programmed to detect any dangerous shift in the heartbeat and, if necessary, shock the heart back into normal rhythm.

The study was prompted by concern that an anti-theft machine's electronic beam could be mistaken by an ICD for an abnormally rapid heartbeat.

Properly labeling anti-theft machines and warning patients of the possible risk of prolonged exposure "should allow patients with ICDs (or pacemakers) to walk through such systems without lingering and therefore be seemingly at no risk of any interaction," researchers concluded.

Researchers tested three common security machines on 169 patients who had implanted defibrillators. The defibrillators were adjusted so that they would not actually deliver a shock to the heart if triggered by the test.

A routine walk-through lasting 10 to 15 seconds caused no disturbance in any of the implantable heart devices. Under extreme exposure--during which people stood within six inches of the transmitter in the security gate for two minutes--19 of the 169 patients had evidence of interference from the anti-theft machines. In most of those 19, it was so minor as to be irrelevant. But seven experienced enough interference to make an inappropriate firing of the defibrillator possible.

Four of the patients also had pacemakers. None experienced any problem.

The study was done by researchers from Indiana University School of Medicine and Methodist Hospital in Indianapolis and the Southwest Florida Heart Group in Fort Myers, Fla. The results were reported last month in Circulation, an American Heart Association journal.

The research was funded partly by an electronics company that makes one kind of anti-theft system. The company played no other role in the design, execution or interpretation of the study.

--Don Colburn


Could a brew a day help keep kidney stones away?

Maybe, according to the latest results of a study of nearly 30,000 male smokers in Finland.

The trial found that drinking a beer a day reduced the risk of kidney stone formation in these men by 40 percent.

Although researchers included other beverages, including wine, distilled spirits, coffee, tea and milk in the study, beer was the only drink that significantly lowered the risk of kidney stones.

All participants in the study were free of kidney stones when they entered the trial.

Kidney stones afflict an estimated 10 percent of Americans at some point during their lifetimes, according to the National Institute of Diabetes and Digestive and Kidney Diseases.

Why drinking beer appears to reduce kidney stone formation is not known. But the team of researchers suggested in the July 15 issue of the American Journal of Epidemiology that the protective effect could be due to the water and alcohol found in beer.

Alcohol depresses the secretion of the hormone vasopressin, which increases urine flow and dilutes the urine. The water in beer could also increase urine output and dilute it.

The hops contained in beer may also provide some protective substances that strongly inhibit the breakdown of bone. "These compounds could therefore slow the release of calcium from bone and reduce calcium excretion," noted the lead author, Tero Hirvonen of the National Public Health Institute in Helsinki.

Since kidney stones are rich in calcium, lowering the calcium concentration in the urine could also account for less kidney stone formation.

The results of the study are drawn from a large lung cancer prevention trial, conducted from 1985 to 1988 in Finland and sponsored by the U.S. National Cancer Institute. Participants ranged in age from 50 to 69 years.

While the study included only male smokers aged 50 and older, the researchers noted that there is "no reason to believe that the associations we observed would be different among nonsmokers, since smoking has not been found to be related to kidney stones.

It is probable that these findings also apply to women and to younger men, since there are no major physiologic differences between these groups regarding kidney stones."

--Sally Squires