Johns Hopkins researchers have new evidence supporting a controversial theory that asthma is partially caused by the failure of deep breaths to relax constricted lung muscles enough to let in more air.
Hopkins researchers exposed asthmatics and non-asthmatics to a drug that makes lung muscles contract, as happens in asthma. They found that non-asthmatics could reduce their reaction to the drug dramatically by taking five deep breaths before exposure, but asthmatics experienced little or no improvement from the deep breaths.
The new finding, funded by the National Institutes of Health, will be announced this week at the annual meeting of the American Academy of Asthma, Allergy and Immunology. It reinforces the results of a 1995 study at Hopkins that used a similar test to show that prohibiting deep breaths increases asthma-like symptoms in non-asthmatics.
"If we can learn more about the mechanisms that create this relaxation of lung muscles, there's a good chance we will be able to use that information to develop new ways to monitor or treat asthma," says Alkis Togias, M.D., who led the study.
Asthma occurs when muscles that line air passages of the lungs become constricted, impairing breathing. Scientists have speculated this results from an unusual reaction by lung muscles to inhaled irritants or allergens, such as pollutants or pollen.
But Togias and others believe that lung muscles in asthmatics and non-asthmatics constrict the same way in response to irritants. They think non-asthmatics can use deep breaths to relax the muscles and open up air passages, while asthmatics can't.
To test the idea, Togias exposed 9 healthy volunteers and 8 asthmatics to methacholine, a drug that makes asthmatics wheeze but normally produces little or no reaction in non-asthmatics. By increasing the dose, Togias reduced non-asthmatics' ability to expel air from their lungs by an average of 25 percent. He also determined how much of the drug was needed to produce the same effect in asthmatics.
His team then exposed each group to methacholine three times. Each time the subject was asked to take no deep breaths for 20 minutes before exposure. On some occasions, though, they were allowed to take several deep breaths immediately prior to inhaling the drug.
Two deep breaths reduced the effects of the methacholine exposure by nearly 66 percent in non-asthmatics. Five deep breaths reduced the effects by approximately 80 percent.
For the asthmatics, though, deep breaths only produced a slight worsening of the methacholine's effects.
Other authors of the presentation were Trisevgeni Kapsali and Solbert Permutt.