Bronchial Thermoplasty 10+ Year Study

Compare rates of severe asthma exacerbations of subjects during the first and fifth year after BT treatment with the proportion of subjects who experience severe asthma exacerbations during the 12 months period prior to enrollment. Compare baseline HRCT scans from subjects from the AIR2 study that enroll in BT 10+ study to examine if there are any clinically significant post-treatment respiratory changes following BT defined as bronchiectasis or bronchial stenosis.