Detecting asthma before the last gasp.

Approximately 5,000 people in the United States will die this year because they can't catch their breath. They suffer from asthma, a disorder in which the lung's airways become narrowed. For some people, asthma produces only mild wheezing. For others, however, the disease can prove lethal.

A Japanese study published in the May 12 NEW ENGLAND JOURNAL OF MEDICINE helps characterize asthmatics who are prone to life-threatening episodes of breathlessness. The report suggests that such people may be slow to recognize a dangerous drop in the blood's concentration of oxygen.

"It's an important study," comments asthma specialist Peter J. Barnes of the National Heart and Lung Institute in London. "It looks like you might be able to predict patients who have a high risk of dying from an asthma attack," he says. Barnes wrote an editorial that accompanies the study.

Kunio Shirato and colleagues at the Tohoku University School of Medicine in Sendai, Japan, studied 11 people who had experienced at least one near-fatal wheezing episode. The team knew that such people face an increased risk of such attacks in the future. They compared these individuals to 11 patients who also suffered from asthma but had never had a potentially deadly bout. The researchers also recruited 16 healthy controls.

The team instructed recruits to breathe through a series of tubes in which resistance increased in stepwise fashion. They discovered that people with a history of near-fatal asthma reported less sensation of breathlessness than other study participants. At high levels of resistance, these patients said they felt out of breath, but they lagged far behind the other asthmatics in their perception of discomfort.

In addition, patients with near-fatal asthma suffered an impaired ability to compensate for low concentrations of oxygen in their blood. Normally, when the oxygen dissolved in blood dips too low, a group of nerve cells (the carotid body) detects the problem and triggers corrective action -- the person starts to breathe more deeply and rapidly.

The scientists found this same drive in people who had had an almost fatal asthma attack, but it was blunted compared to the reactions of other asthmatics and controls.

It may be that some people with asthma inherit an impaired ability to sense and correct low oxygen concentrations in the bloodstream, says Richard J. Martin of the National Jewish Center for Immunology and Respiratory Medicine in Denver.

Such asthmatics may not recognize that they're in deep respiratory trouble until it's almost too late. This tendency to underestimate breathing difficulties may, in turn, lead to a delay in taking medication or going to the hospital, Martin adds. In fact, deaths from asthma have increased in several countries, including the United States, in the last decade.

Additional research may someday provide doctors with an easy-to-use method of identifying patients who run the risk of a near-fatal episode. Until then, Martin believes, all asthmatics should monitor their lung function with a device called a peak flow meter.

Just as a diabetic must monitor his or her blood sugar, asthmatics should rely on an objective measure of their respiratory health, he says. That way, patients who don't feel terribly breathless can recognize a threatening turn in their respiration.