Thermal Dynamics in Newborn and Juvenile Models Cooled by Total Liquid Ventilation

Background: Total liquid ventilation (TLV) consists in filling the lungs with a perfluorocarbon (PFC) and using a liquid ventilator to ensure a tidal volume of oxygenated, CO
₂
-free and temperature-controlled PFC. Having a much higher thermal capacity than air, liquid PFCs assume that the filled lungs become an efficient heat exchanger with pulmonary circulation. Objective: The objective of the present study was the development and validation of a parametric lumped thermal model of a subject in TLV. Methods: The lungs were modeled as one compartment in which the control volume varied as a function of the tidal volume. The heat transfer in the body was modeled as seven parallel compartments representing organs and tissues. The thermal model of the lungs and body was validated with two groups of lambs of different ages and weights (newborn and juvenile) undergoing an ultrafast mild therapeutic hypothermia induction by TLV. Results: The model error on all animals yielded a small mean error of -0.1 ± 0.4 °C for the femoral artery and 0.0 ± 0.1 °C for the pulmonary artery. Conclusion: The resulting experimental validation attests that the model provided an accurate estimation of the systemic arterial temperature and the venous return temperature. Significance: This comprehensive thermal model of the lungs and body has the advantage of closely modeling the rapid thermal dynamics in TLV. The model can explain how the time to achieve mild hypothermia between newborn and juvenile lambs remained similar despite of highly different physiological and ventilatory parameters. The strength of the model is its strong relationship with the physiological parameters of the subjects, which suggests its suitability for projection to humans.