These results appear in the May 1 issue of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
Gerard Cox, M.B., F.R.C.P.C., of the Firestone Institute for Respiratory Health in Ontario, Canada, and four associates examined the safety, impact on lung function and airway responsiveness of bronchial thermoplasty on 16 asthma patients over a two-year period. The study cohort included 6 men and 10 women who had an average age of 39.
On each individual, the researchers performed bronchial thermoplasty to lower the potential for muscle-related bronchoconstriction by reducing the mass of smooth muscle in their airways.
In this 30-minute procedure, doctors applied radio frequency thermal energy directly to the airway through a bronchoscope. This radio frequency energy heated the airway tissue to about 65 degrees Celsius (149 degrees Fahrenheit), a temperature high enough to reduce airway smooth muscle mass, but low enough to avoid tissue destruction and scarring. Three separate sessions were needed to treat all accessible airways of both lungs.
"The procedure was well tolerated," said Dr. Cox. "Side effects were transient and typical of what is commonly observed after bronchoscopy. All subjects also demonstrated improvement in airway responsiveness."
Data collected over 12 weeks from patient-kept diaries indicated that the subjects showed significant improvement in number of symptom-free days, and in morning and evening airway peak flow as determined by a meter. (A peak flow meter is a hand-held device designed to measure how well a person can blow air out of their lungs.)
"A total of 312 adverse events were reported over the 2-year period," said Dr. Cox. "Of these, 230 (74 percent) were 'mild,' 79 (25 percent) were 'moderate' and 3 (1 percent) were 'severe.' All three severe adverse events, which included allergic reaction to peanuts, ovarian cyst and fibroid removal, and partial mastectomy, involved hospitalization and were considered not related to the procedure."
The researchers will continue to follow the study patients for five years to determine if there are longer term safety concerns associated with bronchial thermoplasty.
In an editorial in the same issue of the journal, Elizabeth H. Bel, M.D., Ph.D., of Leiden University Medical Center in The Netherlands, wrote: "This study by Drs. Cox and colleagues is important both from pathophysiologic and clinical points of view. First, it provides a unique insight into the mechanisms of airway hyperresponsiveness in asthma. The ability of asthmatic airways to constrict more promptly and excessively to inhaled stimuli than is the case for normal airways is considered a key factor of the disease, and may be fundamental to its pathogensis."
Dr. Bel continued: "The study, as simple as it is, is uniquely hypothesis-testing and shows that modifying structural elements of the airway wall can profoundly influence airway hyperresponsiveness. Does it indicate that airway smooth muscle is the sole contributor to this characteristic form of asthma? No, unfortunately, is doesn't. Although it is intuitively obvious that airways with reduced muscle mass are likely to contract less in response to stimulation, there are other possibilities, including damage to the nerves or vessels, changes in mucus gland structure and function, alterations in the type of inflammation and changes in airway compliance that may modulate this effect. Thus, the debate on the relative importance of muscular and non-muscular elements in bronchial hyperresponsiveness in asthma has not been resolved by this study."
"From a clinical point of view," Dr. Bel wrote, "the study is even more fascinating because it suggests that bronchial thermoplasty has the potential to become a realistic therapeutic option in chronic asthma not satisfactorily controlled with pharmacotherapy. There are, however, several important issues to be considered. First, the long-term consequences of the procedures are not yet determined. The good news is that over a period of 2 years, none of the serious concerns speculated about, such as the development of fixed obstruction, bronchial instability or chronic progressive tissue damage, have developed. However, one could still envisage adverse effects in the long term."
"A second point of concern is whether the procedure targets the appropriate airways. There is now abundant evidence that distal airways are involved in asthma, particularly in severe asthma. Inadequate treatment of the peripheral airways might be the primary reason why patients with refractory asthma do not respond satisfactorily to inhaled therapy, and are at risk of severe exacerbations. Bronchial thermoplasty does not access the peripheral airways, which may not only be a drawback of the technique, but also may impose risks. If patients refrain from pharmacotherapy after bronchial thermoplasty because of symptomatic improvement, the distal airways might become more inflamed and obstructed than before."
"Whether bronchial thermoplasty will earn a place in the treatment of asthma remains to be determined," Dr. Bel noted. "However, this study shows the potential for a completely new approach of treating asthma and stimulates the development of new hypotheses. For patients with refractory asthma, bronchial thermoplasty might become a real breakthrough, particularly for those with severe airway hyperresponsiveness."
Contact for study: Gerard Cox, M.B., F.R.C.P.C., Firestone Institute for Respiratory Health--T2123, St. Joseph's Healthcare, 50 Charlton Avenue, East Hamilton, ON L8N 4A6, Canada
Phone: (905) 522-1155, ext. 4929
Contact for editorial: Elisabeth H. Bel, M.D., Ph.D., Department of Pulmonology, Leiden University Medical Center, P.O. Box 9600, 23RC, Leiden, The Netherlands
Phone: +31 71 526 2950
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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