Numerical study on cooling characteristics in the distal airway model of the non-heart-beating donor lung cooled by hypothermic ventilation

Abstract

Hypothermic ventilation can protect non-heart-beating donor lung against warm ischemia noninvasively in vivo, and has been expected to solve the problem of severe shortage of donor lung. However, a lack of knowledge of the heat and mass transfer mechanisms during whole process limits the application of this technique in clinical practice. In this case, we investigated the cooling characteristics of this process in a 3D distal airway represent generations 12–19 (G12-19) model, and computational fluid dynamics (CFD) method was used for calculation. The influence of ventilation conditions including Reynolds number (Re), inlet temperature (Tin) and the strengthening effect of droplet spraying were considered. Numerical results indicate that smaller Re instead favor internal cooling in the distal airway. For example, the variation of Re from 10 to 40 will make the outlet temperature of G19 increased from 22.2 °C to 35.9 °C after thermal equilibration (Tin = 10 °C). Adding droplets spraying could improve the cooling efficiency in the distal airway compared with cold air only. Without complete evaporation of the droplets inside the airway (i.e. Re = 10, Tin = 10 °C), the outlet temperature was effectively reduced by 44.0% for G12-15 airway and 51.9% for G16-19 acinus compared to ventilation alone. These findings reveal the reasons for the poor cooling effect of distal airway and can be used to optimize the hypothermic ventilation technique in future.