The unusual symmetric reopening effect induced by pulmonary surfactant

Abstract

This study investigates the stability of a finger of air as it propagates into a liquid-filled model of a liquid-filled model of a pulmonary bifurcation. We seek to elucidate the stability characteristics of the reopening of daughter airways, an event that may be important to the treatment of acute lung disease. To do so, we investigated the symmetry of reopening under conditions of nearly constant surface tension with 1) purified H2O or 2) an anionic surfactant (sodium dodecyl sulfate). Dynamic surface tension was investigated using pulmonary surfactant (Infasurf) with and without the presence of albumin. Flow visualization was accomplished using a microparticle image velocimetry (μ-PIV)/shadowgraph system through which we measured 1) the propagation velocity of the finger of air that reopens each daughter branch, and 2) the instantaneous and averaged velocity field of liquid phase surrounding the tip of the propagating bubble. Only pulmonary surfactant demonstrated the ability of maintaining a nearly symmetric propagation in the daughter channels, which is likely to lead to homogeneous airway reopening. In contrast, when pulmonary surfactant was inactivated by albumin or when the system was held at a nearly constant surface tension, reopening occurred asymmetrically. Our analysis suggests that Infasurf's dynamic surface tension qualities are important to stabilize the removal of liquid obstructions. This demonstrates a new important function of pulmonary surfactant for airway reopening of a multibranched network.

Microscale distribution and dynamic surface tension of pulmonary surfactant normalize the recruitment of asymmetric bifurcating airways

“…1. Therefore comparison of the inlet behavior with various surfactant solutions will provide insight into the effect of nonuniform surfactant distribution on the air-liquid surface of the progressing bubble tip at the inlet region (45).…”

“…2B. Optics principles and system operation are unchanged from the system described in Yamaguchi et al (45,46). Volumetric illumination is provided by a dual-pulse Nd:YAG laser ( ϭ 532 nm, power ϭ 15 mJ/pulse, duration ϭ 4 ns; New Wave Laser Pulse Solo Mini, New Wave Research-ESI, Fremont, CA).…”

“…Since the focal plane of the -PIV measurement is adjusted to the middle of the channel depth, the maximum velocity of the channel can be closely approximated and then converted to an average flow rate by using rectangular duct flow profiles, following Ref. 45. We define t ϭ 0 as the moment when the progressing interface reaches the carina.…”

“…Successful full-lung models will require an understanding of the interactions that occur in the region of a bifurcation and the relative responses of daughter airways. In a previous study (45), we initiated investigations of the recruitment of bifurcating airways, following prior studies by others (3). That study investigated the microfluidic behavior of reopening a simple symmetric Y-shape channel-this demonstrated pulmonary surfactant's unique ability to maintain nearly symmetric recruitment of daughter airways, which could improve the likelihood of uniform recruitment of a multigenerational bifurcated network and thus maximize the potential for global opening.…”

The influence of tethering and gravity on the stability of compliant liquid-lined airways

“…We developed a small diameter compliant vessel of approximately 2.0 mm ID when fully inflated to be consistent with pulmonary airways that is transparent for visualization. We elected to construct this vessel using polydimethylsiloxane (PDMS) for which we have experience in the development of microfluidic models of aspects of the pulmonary system (Yamaguchi et al, 2014).…”