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.