Theoretical and experimental evaluation of a simple cooling pad for inducing hypothermia in the brain and in the spinal cord following traumatic spinal cord injury

This dissertation investigates the temperature in the torso and head during selective hypothermia using a cooling pad. The Pennes bioheat equation and finite element analysis are used to predict the temperatures in the spinal cord, the brain and the cerebrospinal fluid (CSF) during hypothermia. Following 30 minutes of cooling (Tcool = 20°C), the temperature in the CSF and the spinal cord is reduced by more than 2.5°C. The spinal cord temperature is sensitive to the spinal cord blood perfusion rate, the cooling temperature, the cooling pad width, and the CSF velocity. The temperature in the grey matter is reduced by approximately 1°C, while the temperature in the white matter remains normal after 90 minutes of cooling. Ischemia in the grey matter increases cooling extent to the brain. For the in vivo animal study, a cooling pad is used to induce hypothermia in rats to test its effectiveness in a biological environment. Coolant is circulated through the pad to induce mild or moderate hypothermia in spinal cord. During mild hypothermia, the temperature on the back and in the spine is reduced by 8.76+/-0.31°C and 6.67+/-0.1°C, respectively. The temperature in the spine and on the back is reduced by 11.88+/-3.85°C and 17.9+/-1.46°C, respectively, during moderate hypothermia. A difference between the brain and rectal temperatures suggests mild cooling in the brain tissue. A numerical model of the rat head and torso is developed to compare the experimental and theoretical predictions of the tissue temperatures following mild and moderate hypothermia. Theoretical predictions and experimental measurements in both the torso and head regions are in reasonable agreement. However, differences between the experimentally acquired and theoretically predicted temperatures in the brain may be due to the blood flow response to cooling in the brain tissue and imperfect mixing of the warm CSF and cold spinal fluid. The present study provides a foundation for developing a cooling protocol to prevent secondary injury to neurological tissue following traumatic injury that affects the entire central nervous system (CNS).