Complex modeling of the human lung has shown a likely explanation for how bronchial thermoplasty reduces health care needs and improves quality of life in patients with moderate to severe asthma.
The study found the observed benefits of bronchial thermoplasty could be explained by changes in whole-lung flow patterns, induced by structural changes in the treated airways.
Previously, it was thought that the small number of large airways treated during bronchial thermoplasty was insufficient to explain the observed benefits in what has been a controversial procedure.
The study used whole left lung specimens from non-asthma controls, non-respiratory deaths in people with asthma and confirmed asthma deaths, to create mathematically simulated lungs.
The research team was able to simulate lung structure and function and calculate airflow pre and post simulated bronchial thermoplasty.
The bronchial thermoplasty protocol was based on current clinical practice – treating the lower lobe bronchus, upper lobe bronchus, superior division bronchus and LB1-10 to effect a 75% reduction in airway smooth muscle.
They found that central airway structural changes trigger global flow redistribution toward more homogeneous and efficient flow patterns.
“It arises from the structural alteration of a small number of treated central airways only – no other mechanisms are required…,” they said.
Coauthor Professor Alan James, from the Department of Pulmonary Physiology and Sleep Medicine at Sir Charles Gairdner Hospital, told the limbic one of the challenges was that the distribution of smooth muscle in the lung was quite variable.
“The modeling shows that variability in the distribution of this muscle may be just as important as how much muscle there is but it also explains why just burning some of the airways might actually still be effective.”
“And it might be that we need to characterise where that muscle is and if we can do that, then we might be able to achieve better outcomes with bronchial thermoplasty and other treatments we can think about to try and reduce the muscle.”
Professor James said there was still some skepticism about using bronchial thermoplasty in the absence of a clear-cut biomarker or indicator of who would benefit most.
“There do seem to be patients where it works really well. One the problems is some of the data haven’t used good controls, which is obviously difficult, and the follow-up is not as much as we would like but that is slowly building.”
“So the bottom line is yes, bronchial thermoplasty can be effective but probably more effective in some patients than others and we need to be able to try and detect muscle or some other marker which can work out which patients will respond best to bronchial thermoplasty or other treatments directed towards smooth muscle.”
He said he was currently involved in developing a method to measure airway smooth muscle using laser technology via a bronchoscope.