The Feasibility of Continuous Bronchoscopy During Exercise in Healthy Adults in Assessing Large Airways Collapse

The large central airways (i.e. trachea and bronchi) act as a conduit to enable lower airway ventilation but also facilitate airway clearance during dynamic manoeuvres, such as coughing. It is becoming increasingly well recognised however, that in a significant proportion of individuals with chronic airway disease (e.g. chronic obstructive pulmonary disease or chronic asthma) and in those with an elevated body mass index (BMI), that the large airways may exhibit a tendency to excessive closure or narrowing. This large airway collapse (LAC) can be associated with exertional breathlessness and difficulty clearing airway secretions. A variety of terms have been used to describe LAC including excessive dynamic airway collapse (EDAC) or if the cartilaginous structures are involved then tracheobronchomalacia (TBM).

At the current time, there is considerable debate regarding the definition of LAC. Typically the 'excessive' collapse underpinning a 'diagnosis' of EDAC is defined as excessive bulging of the posterior tracheal membrane into the airway lumen during expiration without associated collapse of the cartilaginous rings, however the degree to which the trachea closes, to constitute EDAC is debated, with literature varying from >50% to >90%. Moreover, partial expiratory airways collapse (up to 50% reduction in airways cross-sectional area) can be identified in 70-80% of healthy individuals during dynamic computed tomography (CT).

One clear limitation of the current approach to diagnosis is the fact that many of the 'diagnostic' tests employed, utilise static, supine measures +/- forced manoeuvres. These are somewhat physiologically flawed and differ markedly from the reality of the heightened state of airflow that develops during exertion. i.e. forced manoeuvres likely induce very different turbulent and thoracic pressure changes, in contrast to the hyperpnoea of real-life physical activity (i.e. walking or cycling). A current unanswered question is therefore, what happens to the large airway dynamic movement of healthy individuals (and ultimately patients) during real-life exercise and how does this compare with the measures taken during a forced manoeuvre, either during a bronchoscopy or during an imaging study such as CT or MRI scan.

The key aim of this study is therefore to evaluate and characterize large airway movement in a cohort of healthy adults during a real-life exercise challenge and to compare this with findings from a dynamic expiratory MRI and MRI during exercise. In order to achieve this, the investigators propose to develop and test the feasibility of an exercise-bronchoscopy protocol.

As a clinical service, the investigators have extensive experience of evaluating movement of the upper airway and larynx during strenuous exercise. The Principal Investigator currently performs over 100 continuous laryngoscopy during exercise (CLE) tests per year, whereby a small laryngoscope is placed in the upper airway and is secured on a headgear to allow visualisation of the laryngeal and subglottic movement during exercise. i.e. whilst a subject performs running exercise. This test has an established role in patient evaluation and a proven safety record in the assessment of laryngeal closure during exercise. The research team has performed approximately 500 CLE tests in the Royal Brompton Hospital, with no serious adverse outcome.