Lung Compliance and Resistance Following Bronchial Thermoplasty in Severe Persistent Asthma: A Pilot Study and Discussion of the Physiology
Rationale: Bronchial thermoplasty reduces airway smooth muscle mass, bronchoconstriction and symptoms in severe, persistent asthmatics. Despite its application only to larger airways (> 3 mm), it is not known if small airways are also affected by bronchial thermoplasty.
Objective: To determine if thermoplasty also affects the smaller airways (< 3 mm in diameter) before and after bronchial thermoplasty. Methods: Lung resistance, static and dynamic lung compliance were measured using the esophageal balloon technique before and after undergoing bronchial thermoplasty in 5 patients.
Results: All patients described improved symptoms and reduced use of short-acting bronchodilators within a few weeks following completion of bronchial thermoplasty. Pre-thermoplasty, all patients exhibited significant frequency dependency of lung compliance, with dynamic lung compliance decreasing to as much as 75% of baseline static compliance value at maximum respiratory rate. In 4 of 5 patients, post-thermoplasty values for dynamic lung compliance were higher than pre-thermoplasty over the range of respiratory rates. Post-thermoplasty, static lung compliance did not change significantly from pre-thermoplasty values. Lung resistance during quiet breathing (baseline) decreased in 4 of 5 patients following thermoplasty, and decreased at higher respiratory frequencies in 4 of 5 patients.
Conclusions: Patients with severe persistent asthma exhibit increased resting lung resistance and frequency dependence of compliance, the magnitudes of which are in ameliorated following bronchial thermoplasty, and associated with variable frequency dependence of lung resistance not apparent before bronchial thermoplasty. Bronchial thermoplasty likely exerts its effects on small as well as large airways.