Poiseuille’s equation describes the relationship between fluid viscosity, pressure, tubing diameter, and flow, yet it is not known if cold organ perfusion systems follow this equation. We investigated these relationships in an ex vivo model and aimed to offer some rationale for equipment selection. Increasing the cannula size from 14 to 20？Fr increased flow rate by a mean (SD) of 13 (12)%. Marshall’s hyperosmolar citrate was three times less viscous than UW solution, but flows were only 45% faster. Doubling the bag pressure led to a mean (SD) flow rate increase of only 19 (13)%, not twice the rate. When external pressure devices were used, 100？mmHg of continuous pressure increased flow by a mean (SD) of 43 (17)% when compared to the same pressure applied initially only. Poiseuille’s equation was not followed; this is most likely due to “slipping” of preservation fluid within the plastic tubing. Cannula size made little difference over the ranges examined; flows are primarily determined by bag pressure and fluid viscosity. External infusor devices require continuous pressurisation to deliver high flow. Future studies examining the impact of perfusion variables on graft outcomes should include detailed equipment descriptions. “This paper is dedicated to Professor Paul Callaghan FRS, who died during its completion” 1. Introduction Adequate organ preservation is essential to subsequent graft function and is therefore fundamental to successful organ transplantation. Despite the introduction of machine perfusion [1–6], the overwhelming majority of organ procurements still take place with standard techniques using intravascular instillation of cooled preservation fluids and cold storage. However, although preservation fluids have been investigated extensively [7–10], comparatively little research has been carried out on the optimal method of delivering them [11]. Preservation fluid pressure appears to influence graft function [12–17], but it is also likely that fluid flow rate is clinically important, as heat transfer, and therefore organ cooling, is flow-dependent [18], and rapid organ cooling has been shown to improve cellular and organ viability [19, 20]. These two variables are interrelated, and many clinicians would assume that Poiseuille’s equation adequately describes this relationship. Poiseuille’s equation states that fluid flow rate ( ) through a tube is inversely proportional to tube length ( ) and fluid viscosity ( ) and is proportional to the pressure drop across the tube ( ) and the tube radius ( ) to the fourth power [21]: However, Poiseuille’s
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