In cardiac surgeries, when cardiopulmonary bypass (CPB) (or extracorporeal circulation (ECC)) is employed, the lungs are temporarily disconnected from the body. To minimize the risk of tissue damage or respiratory complications, the lungs are subjected to mild hypothermia. Incorporating dynamic heat transfer modeling offers the potential to enhance temperature regulation through a more advanced approach. A complex thermal model, based on a thermal two-port network, offers a wide frequency range applicability, making it suitable for modeling the human breathing frequencies. This modeling approach can also be adapted to incorporate the influence of blood flow, which serves as a natural temperature regulator in the human body. This is accomplished by combining the thermal two-port network with the bio-heat equation. The main contributions focus on introducing distinctive and simplified approximation models for the equivalent global impedance of thermal transfer within the lungs. These models, featuring minimal parameters, manifest comparable dynamic traits in the frequency domain, akin to the attributes of the two-port network model. This progress clears the way for broader utilization across various domains.Read less <