Estimation of the Pressure Drop Required for Lymph Flow through Initial Lymphatic Networks

Abstract

Background: Lymphatic function is critical for maintaining interstitial fluid balance and is linked to multiple pathological conditions. While smooth muscle contractile mechanisms responsible for fluid flow through collecting lymphatic vessels are well studied, how fluid flows into and through initial lymphatic networks remains poorly understood. The objective of this study was to estimate the pressure difference needed for flow through an intact initial lymphatic network. Methods and Results: Pressure drops were computed for real and theoretical networks with varying branch orders using a segmental Poiseuille flow model. Vessel geometries per branch order were based on measurements from adult Wistar rat mesenteric initial lymphatic networks. For computational predications based on real network geometries and combinations of low or high output velocities (2 mm/s, 4 mm/s) and viscosities (1 cp, 1.5 cp), pressure drops were estimated to range 0.31-2.57 mmHg. The anatomical data for the real networks were also used to create a set of theoretical networks in order to identify possible minimum and maximum pressure drops. The pressure difference range for the theoretical networks was 0.16-3.16 mmHg. Conclusions:The results support the possibility for suction pressures generated from cyclic smooth muscle contractions of upstream collecting lymphatics being sufficient for fluid flow through an initial lymphatic network.

Lymphatic Vessel Network Structure and Physiology

“…The geometry of networks also contributes to the overall efficiency of flow. Based on the network geometry of initial lymphatics and precollectors in rat mesentery, computational models estimate that a downstream pressure drop in the range of 0.3 to nearly 3.0 mmHg is needed for reasonable flow through the network (999). While precollectors have traditionally been thought to be passive conduits that lead to collecting lymphatics, how such a gradient is established is poorly understood.…”

“…There has been some evidence for the presence of discontinuous circular smooth muscle cells (1196) that may assist with movement of lymph. Another popular concept is that the downstream collecting lymphatics, through pumping, cause a suction effect (473, 999). Additional work is needed to elucidate these mechanisms.…”

Demonstration and Analysis of the Suction Effect for Pumping Lymph from Tissue Beds at Subatmospheric Pressure

“…Schmid-Schönbein 9 estimated for a hypothetical tissue cylinder of 1 mm radius drained by an initial lymphatic of 10 µm radius that the pressure drop required for adequate transport of fluid from the tissue space to the initial lymphatic would be only 0.12 cmH 2 O. Furthermore, a recent study estimated the viscous pressure drop through an initial lymphatic network to range from 0.4 to 3.5 cmH 2 O 24 . These estimates indicate that the transient pressure drops during suction suffice to open the primary valves and facilitate lymph formation.…”

“…The resistance provided by the upstream initial lymphatics, estimated by Sloas et al . 24 , was included in both our experiments and models. In isolated vessels pumping with an increased inflow resistance upstream, additional work was required for the passive re-expansion of the vessel to draw fluid in.…”

“…The total upstream resistance (after adding the additional resistance) was similar to that reported by Sloas et al . 24 , who estimated the flow resistance of an excised network of initial lymphatics leading to collecting lymphatics. Thus, the requirement for pipettes to perform these experiments simulates the conditions experienced by these vessels in vivo .…”