Hypothermic brain protection strategies using thermal models
Doctor of Philosophy
The brain is the organ at greatest risk of injury during periods of reduced blood flow; to prevent tissue death and protect organ function in such conditions, hypothermia is used. The primary goal of this research is to use a thermal model as a tool to develop and optimize hypothermic protection methods for the brain tissue given the fact that the cooling time, as well as the degree of temperature reduction required for successful outcome are still uncertain, and the knowledge of brain temperature is desirable during clinical treatment, but highly destructive. To improve the existing thermal models of brain, the effect of the temperature over the metabolic heat generation, and the regulatory processes that control the cerebral blood perfusion were incorporated in this project. The proposed thermal model was validated using data obtained from experiments of perinatal asphyxia, and different cooling strategies on swine. The temperature calculations show the same behavior and tendencies observed experimentally, and the importance of accurate thermal properties and anatomy in the temperature prediction is observed. Based on these observations, a realistic geometric model of the human head obtained from tomographic data was created to study cooling and rewarming during brain ischemia produced by circulatory arrest and stroke. The calculations performed have helped to understand the importance of the tissue temperature gradients in the success of hypothermic therapies. The calculations show that hypothermic cardiopulmonary bypass (CPB) together with external head cooling help reduce the temperature gradients within the head during periods of reduced blood flow, and reduce the temperature increase in the deep tissue produced by the residual cerebral metabolic activity. The results of this research can be used in the refinement of cooling techniques used in the treatment of brain injury, ischemia, asphyxia and to improve organ protection during surgery.
Physiology; Biomedical engineering; Mechanical engineering