Effect of Continuous Positive Airway Pressure (CPAP) on 6-Minute Walk Test Outcomes in Patients With Excessive Central Airway Collapse (ECAC)

Basal 6MWT performed as a standard of care in these patients will be compared to intervention ones to see if there is an improvement of at least 24 meters in their 6MWT distance, then both groups will be compared to see if there is a statistically significant difference between groups. Subjects, treating physicians and the research fellow performing the 6MWT will be blinded to the intervention; the only un-blinded personnel to the intervention will be the study coordinator who will be in charge of setting the CPAP before every intervention.

As part of the standard of care of our institution, patients that are referred due to suspicion of ECAC undergo initial PFTs, 6MWT and dynamic CT scan. With this information, patients are evaluated in clinic by the interventional pulmonary and thoracic surgery team who decide if the patient has the mentioned disease based on the previous testing. To corroborate the findings patients with moderate so severe disease are taken into a bronchoscopy with dynamic maneuvers as part of the standard of care. Initial bronchoscopic examination will be performed as described in the following section "I-Dynamic Bronchoscopy Protocol" as part of the standard of care of patients. After initial evaluation, during the same intervention, all patients that agree to participate in our study will go through a CPAP calibration procedure; in order to determine the adequate pressure to achieve airway patency of at least 70% during end exhalation in each individual case. After regular bronchoscopic examination, a full face F&P SimplusTM CPAP mask (Fisher & Paykel, Irvine, CA, USA) will be placed in all patients to prevent un-blinding the treating physician. The mask will be connected to a dual axis swivel adapter (T-adapter) and the bronchoscope will be advanced to the nares through the swivel adaptor; air leak will be prevented by the tight disposable cap of the swivel adaptor as described by Murgu et al.20

The calibration process will be performed following the technique first described by Ferguson et al10, bronchoscope will be positioned to assess the area with ECAC previously identified during regular examination; bronchoscope will be placed in the center of the lumen while assuring a constant 1-cm distance between the tip of the bronchoscope and the target area being measured, images will be taken during end inspiration and end expiration, gradual increases of 1 cmH2O in the CPAP pressure will be made until a 70% or less collapse is seen during end expiration by the bronchoscopist. At any given pressure increase the assessment of airway collapse will be made in 3 different respiratory cycles, the whole procedure will be recorded and posteriorly analyzed using morphometric bronchoscopy (Image J analysis program) as described in the "Morphometric Bronchoscopy" section.

Patient Population Subjects (>18 years of age) with previous diagnosis of ECAC confirmed by dynamic CT scan and/or bronchoscopy, who are currently receiving adequate medical therapy (Optimal medication doses and interventions defined by Interventional Pulmonary team) for comorbidities such as COPD, GERD, asthma, etc and are able to perform a 6 MWT.

Tracheobronchomalacia Evaluation CT Central Airway Protocol: All patients will be imaged according to our standard low dose CT central airway protocol21, which includes imaging during end-inspiratory and continuous dynamic expiratory phases. A multidetector row, helical CT scanner (LightSpeed; GE Medical Systems; Milwaukee, WI; or Aquilion; Toshiba America Medical Systems; Tustin, CA) which includes 4, 8, 16, and 64 detector-row systems will be used. Helical scanning will be performed in the cranio-caudal dimension during both respiratory phases. An experienced thoracic radiologist will review the CT images on a picture archiving and communication system (PACS) [Path-Speed, General Electric Medical Systems]. Using a computerized tracing tool in our PACS system, the inner wall of the airway will be hand traced at the level of maximal collapse in dynamic expiratory images to calculate the cross-sectional area of the airway (mm2). At the same level on end-inspiration images, the cross-sectional area of the airway lumen will be determined by using the same method. The percentage of luminal collapse between both respiratory phases will be calculated using the following formula= [1 - (Aee/Aei)],) X100, where Aee is luminal area at end expiration and Aei is luminal area at end inspiration. Mild ECAC is diagnosed if the percent of luminal collapse during dynamic expiration is 70-80%, moderate from 80-90% and severe >90%.