Abstract
The authors have previously presented a mathematical model to predict transit time of a neutrophil through an alveolar capillary segment which was modeled as an axisymmetric arc-shaped constriction settled in a cylindrical straight pipe to investigate the influence of entrance curvature of a capillary on passage of the cell. The axially asymmetric cross section of a capillary also influences the transit time because it requires three-dimensional deformation of a cell when it passes through the capillary and could lead to plasma leakage between the cell surface and the capillary wall. In this study, a rectangular channel was introduced, the side walls of which were moderately constricted, as a representative of axially asymmetric capillaries. Dependence of transit time of a neutrophil passing through the constriction on the constriction geometry, i.e., channel height, throat width and curvature radius of the constriction, was numerically investigated, the transit time being compared with that through the axisymmetric model. It was found that the transit time is dominated by the throat hydraulic diameter and curvature radius of the constriction and that the throat aspect ratio little affects the transit time with a certain limitation, indicating that if an appropriate curvature radius is chosen, such a rectangular channel model can be substituted for an axisymmetric capillary model having the same throat hydraulic diameter in terms of the transit time by choosing an appropriate curvature radius. Thus, microchannels fabricated by the photolithography technique, whose cross section is generally rectangular, are expected to be applicable to in vitro model experiments of neutrophil retention and passage in the alveolar capillaries.
Highlights
The function of the lung is to oxygenate the blood and to remove carbon dioxide
It is known that approximately one half of the neutrophils, the most common type of leukocyte, stop at least once during their journey through the lung [1,2] and that it takes some neutrophils more than 20 min. to pass through the pulmonary capillary bed [3], while erythrocytes flow through the lung in a few seconds with little or no observable delay [4,5]
Neutrophil Model Various rheological models have been proposed for a neutrophil: a homogeneous sphere composed of standard viscoelastic material [26,27], a Newtonian liquid drop with a shell-like surface layer under tension [14,28], a model in which the inner Newtonian liquid is replaced by a Maxwell fluid [29,30] or by a power-law fluid [31], and a three-layer or compound drop model in which the cortical membrane of the lipid bilayer, the cytoplasm and the nucleus are taken into consideration [32,33,34]
Summary
The function of the lung is to oxygenate the blood and to remove carbon dioxide. For this purpose, the lung is made up of an aggregation of alveoli and a dense network of capillaries surrounding individual alveoli. To pass through the pulmonary capillary bed [3], while erythrocytes flow through the lung in a few seconds with little or no observable delay [4,5] This retention leads to a 40- to 100-times higher concentration of neutrophils in the pulmonary capillary bed than in systemic large vessels [6,7]. These highly concentrated neutrophils are thought to help the lung to effectively eliminate foreign infectious substances brought in with inhaled air. In the pulmonary capillaries, deformation characteristics of neutrophils, in addition to the highly interconnected structure of the capillary network, are thought to account for their longer transit time and the resultant high concentration
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
