title: Effect of gravity on liquid plug transport through an airway bifurcation model.
abstract: Many medical therapies require liquid plugs to be instilled into and delivered throughout the pulmonary airways. Improving these treatments requires a better understanding of how liquid distributes throughout these airways. In this study, gravitational and surface mechanisms determining the distribution of instilled liquids are examined experimentally using a bench-top model of a symmetrically bifurcating airway. A liquid plug was instilled into the parent tube and driven through the bifurcation by a syringe pump. The effect of gravity was adjusted by changing the roll angle (phi) and pitch angle (gamma) of the bifurcation (phi = gamma =0 deg was isogravitational). Phi determines the relative gravitational orientation of the two daughter tubes: when phi not equal to 0 deg, one daughter tube was lower (gravitationally favored) compared to the other. Gamma determines the component of gravity acting along the axial direction of the parent tube: when gamma not equal to 0 deg, a nonzero component of gravity acts along the axial direction of the parent tube. A splitting ratio Rs, is defined as the ratio of the liquid volume in the upper daughter to the lower just after plug splitting. We measured the splitting ratio, Rs, as a function of: the parent-tube capillary number (Cap); the Bond number (Bo); phi; gamma; and the presence of pre-existing plugs initially blocking either daughter tube. A critical capillary number (Cac) was found to exist below which no liquid entered the upper daughter (Rs = 0), and above which Rs increased and leveled off with Cap. Cac increased while Rs decreased with increasing phi, gamma, and Bo for blocked and unblocked cases at a given Cap > Ca,. Compared to the nonblockage cases, Rs decreased (increased) at a given Cap while Cac increased (decreased) with an upper (lower) liquid blockage. More liquid entered the unblocked daughter with a blockage in one daughter tube, and this effect was larger with larger gravity effect. A simple theoretical model that predicts Rs and Cac is in qualitative agreement with the experiments over a wide range of parameters.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zheng
authors.forename: J C
authors.initials: JC
authors.lastname: Anderson
authors.forename: V
authors.initials: V
authors.lastname: Suresh
authors.forename: J B
authors.initials: JB
authors.lastname: Grotberg
mesh_terms: D001692:Biological Transport / Q000502:physiology; D001826:Body Fluids / Q000502:physiology*; D001992:Bronchoalveolar Lavage Fluid; D003198:Computer Simulation; D006112:Gravitation; D006801:Humans; D008168:Lung / Q000502:physiology*; D044085:Microfluidics / Q000379:methods*; D008954:Models, Biological; D011663:Pulmonary Surfactants / Q000378:metabolism*; D015656:Respiratory Mechanics / Q000502:physiology*
chemical_list: D011663:Pulmonary Surfactants