A device that uses radio waves to heat the muscle lining of patients' airways appears to treat their asthma, according to a new study.
Just three sessions of the new treatment cut the number of mild asthma attacks in patients by a half during a one-year trial, researchers say. The probe reduces inflammation in the bronchial tubes, doctors believe, and could lessen asthmatics' need for steroids.
Gerard Cox at McMaster University in Hamilton, Ontario, Canada, and colleagues recruited 112 adults with moderate to severe asthma. All of the patients received inhaled steroids and other drugs to treat their breathing difficulties as needed. But half of the group also underwent three sessions of the new radiofrequency treatment under a mild anaesthetic to avoid discomfort.
The procedure, known as bronchial thermoplasty, involves inserting a long, thin catheter probe through the nose or mouth to reach the lung airways. Once the probe is in place, the tip is heated using radio waves. This raises the temperature in the muscle tissue of the airway up to 65°C for 10 seconds. Watch a video with narrative of the procedure in action.
The probe is slowly moved up the airway to expose sections of the bronchial tubes to these brief periods of heat. The heat generated by the device over several treatments causes a reduction in the smooth muscle lining the airways - though exactly how this happens remains unclear.
Smooth muscle provides essential structural support to keep airways open and helps clear mucus. However, people with asthma typically have excessive amounts of this type of muscle in their lungs. A growing body of evidence suggests that this extra smooth muscle in asthmatics contributes to inflammation, which might in turn cause the symptomatic narrowing of airways.
At the end of the one-year trial, the subjects who received bronchial thermoplasty treatments reported an average of 10 mild asthma attacks over the course of the study - roughly 50% fewer than those who received asthma drugs only. The researchers defined "mild" asthma attacks as those that did not warrant a hospital visit.
Cox says there were too few severe asthma attacks during the study to determine whether the treatment had a statistically significant impact on these severe attacks.
The patients who received the experimental heat treatment were free of asthma symptoms for 40% of days during the year, on average. Those who did not receive thermoplasty were symptom-free for only 17% of the days.
Steroid side effects
The new study was funded by the company Asthmatx, which has developed the thermoplasty technique for the lungs but has not yet applied to the US Food and Drug Administration for approval to market the technique.
Cox, who is not employed by Asthmatx, says the treatment may improve asthmatics' breathing and reduce their dependence on asthma drugs such as steroids. Inhaled steroids can sometimes cause side effects including mouth infections.
But he adds that the thermoplasty procedure itself could have unwanted effects, such as creating scar tissue in the airways, though this was not seen in the recent trial.
Other doctors say that thermoplasty could play a role in asthma treatment in the future. They stress, however, that the probe can only fit in passageways greater than 3 millimetres in diameter, meaning that it cannot directly treat the tiniest airways in the lungs.
Journal reference: New England Journal of Medicine (vol 356, p 1327)
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