Effect of Bronchial Thermoplasty on Airway Closure

BACKGROUND: Bronchial Thermoplasty, a procedure that applies thermal energy to the airway wall has been shown to impair the ability of airway to contract in response to methacholine chloride (Mch). The technique has been advocated as an alternative treatment for asthma that may permanently limit airway narrowing. In previous experimental studies in dogs and humans, it was shown that those airways treated with bronchial thermoplasty had significant impairment of Mch responsiveness. METHODS: In the present study, we investigated the ability of canine airways to close completely with very high concentrations of Mch after bronchial thermoplasty. Bronchial thermoplasty was performed on dogs using the Alair System, comprising a low power RF controller and a basket catheter with four electrodes. A local atomization of Mch agonist was delivered directly to the epithelium of the same airway locations with repeated challenges. Airway size was measured with computed tomography, and closure was considered to occur in any airway where the lumen fell below the resolution of the scanner (< 1 mm). RESULTS: Our results show that, while treated airways still have the capacity to close at very high doses of Mch, this ability is seriously impaired after treatment, requiring much higher doses. CONCLUSIONS: Bronchial thermoplasty as currently applied seems to simply shift the entire dose response curve toward increasing airway size. Thus, this procedure simply serves to minimize the ability of airways to narrow under any level of stimulation.