Passive Pressure–Diameter Relationship and Structural Composition of Rat Mesenteric Lymphangions

Abstract

Background: Lymph flow depends on both the rate of lymph production by tissues and the extent of passive and active pumping. Here we aim to characterize the passive mechanical properties of a lymphangion in both midlymphangion and valve segments to assess regional differences along a lymphangion, as well as evaluating its structural composition. Methods and Results: Mesenteric lymphatic vessels were isolated and cannulated in a microchamber for pressure-diameter (P-D) testing. Vessels were inflated from 0 to 20 cmH 2 O at a rate of 4 cmH 2 O/min, and vessel diameter was continuously tracked, using an inverted microscope, video camera, and custom LabVIEW program, at both mid-lymphangion and valve segments. Isolated lymphatic vessels were also pressure-fixed at 2 and 7 cmH 2 O and imaged using a nonlinear optical microscope (NLOM) to obtain collagen and elastin structural information. We observed a highly nonlinear P-D response at low pressures (3-5 cmH 2 O), which was modeled using a three-parameter constitutive equation. No significant difference in the passive P-D response was observed between mid-lymphangion and valve regions. NLOM imaging revealed an inner elastin layer and outer collagen layer at all locations. Lymphatic valve leaflets were predominantly elastin with thick axially oriented collagen bands at the insertion points. Conclusions: We observed a highly nonlinear P-D response at low pressures (3-5 cmH 2 O) and developed the first constitutive equation to describe the passive P-D response for a lymphangion. The passive P-D response did not vary among regions, in agreement with the composition of elastin and collagen in the lymphatic wall.

Quantification of the passive and active biaxial mechanical behaviour and microstructural organization of rat thoracic ducts

“…Interface 12: 20150280 circulation [13,34,35]. Loaded thicknesses in rat thoracic ducts reported in the literature are consistent with the present data [9,13]; geometric and functional parameters generally have large standard errors, suggesting large sample-to-sample variations. Similarly, others have used confocal microscopy to quantify angle orientation in bovine mesenteric lymphangions and report similar variability to that reported herein [12].…”

“…The mechanical environment probably contributes significantly to the overall contractile function of these vessels, leading some to study the relationship between intrinsic contractile function and mechanical cues such as magnitude and direction of flow, inlet and outlet pressure, or pressure gradient [3][4][5][6][7]. Also directly related to contractile function is the ability of the vessel to distend appropriately in response to mechanical loading, motivating studies that characterize the active and passive mechanical behaviour of lymphatic vessels [8][9][10][11]. Confocal microscopy has also been reported to characterize the vessel microstructure and geometry, which dictate the mechanical responses of the vessels [9,12].…”

Parameter sensitivity analysis of a lumped-parameter model of a chain of lymphangions in series

“…The existence of an optimum value of external pressure, at values slightly greater than inlet pressure p a , may explain why external compression as therapy for lymphedema works for only a small percentage of patients (28). However, recent experiments by Rahbar et al (19) showed that the vessel remains in its most compliant state over a wider range of diameters than is the case for the pressure-diameter relationship used in this study. Consequently, the range of optimal external pressures in vivo may be wider than that which we have shown here.…”

Mechanical forces and lymphatic transport

“…Passive tension is dependent upon the connective tissue in the lymphatic wall, which contains an abundance of collagen and elastin fibers (Rahbar et al, 2012). Recent studies of the passive properties of rat mesenteric lymphatics showed that these vessels are compliant at the low intraluminal at which they typically operate (1–5 cm H 2 O).…”