To better understand bronchoconstriction in asthma, it is critical to dynamically visualize airway behavior in vivo. However, currently available imaging techniques do not have sufficient temporal and spatial resolution to investigate airway dynamics. We propose to use endobronchial Optical Coherence Tomography (OCT) to provide real-time cross-sectional images of airway dynamics with a high spatial resolution. Our aim was to study the structure and function of spatially distinct airways during tidal breathing (TB), breath-holds (BH) at end inspiration, and in a response to single deep inspiration (DI) and multiple DI (MDI) in a preclinical sheep asthma model.
Anesthetized and mechanically ventilated sheep (n=3) were imaged with OCT in 4 dependent and 4 non-dependent airways at baseline and in methacholine constricted airways. We assessed airway morphology during TB, BH, DI and MDI maneuvers.
The change in airway lumen area was found to be greater in the dependent airways compared to the non-dependent airways during TB (dependent: +14.9%, non-dependent: +6%) at baseline. Similarly, the dependent airways dilated more than the non-dependent airways in response to BH (dependent: +7.9%, non-dependent: +5.7%) in relaxed condition. Conversely, in the constricted lung, the DI and MDI maneuvers dilated the non-dependent airways (+13.6% DI, +44% MDI) more than the dependent airways (+6% DI, +15.5% MDI). Overall, dependent airways were more distensible than non-dependent airways during TB and BH, while this behavior was reversed following DI and MDI maneuvers in constricted airways possibly due to a greater local methacholine delivery due to gravitational dependencies on perfusion.