Brain hypothermia induced by a temperature reduction of the spinal fluid using a torso-cooling pad is evaluated as a cooling alternative for traumatic injury patients. A theoretical model of the human head is developed to include its tissue structures and their contribution to local heat transfer. The Pennes bioheat equation and finite element analysis are used to predict the temperature distribution in the head region. The energy balance in the cerebrospinal fluid (CSF) layer surrounding the brain during mixing of the CSF and cold spinal fluid is also formulated to predict the CSF temperature reduction. Results show that the presence of cooled CSF around the brain provides mild cooling (approximately 1 degrees C) to the grey matter within 3000 s (50 min) with a cooling capacity of approximately 22 W. However, large temperature variations (approximately 3.5 degrees C) still occur in the grey matter. This approach is more effective during ischemia because it promotes deeper cooling penetration and results in larger temperature reductions; the average grey matter temperature decreases to 35.4 degrees C. Cooling in the white matter is limited and only occurs under ischemic conditions. The non-invasive nature of the torso-cooling pad and its ability to quickly induce hypothermia to the brain tissue are beneficial to traumatic injury patients.

Although significant damage is caused by the mechanics of the traumatic spinal cord injury (SCI), secondary injury that follows is often times even more dangerous. It occurs within the first 12–24 hours following the injury and can last up to 5–10 days, depending on the severity of the injury [1]. Secondary injury causes physiological disturbances that disrupt the body’s homeostasis like initiating a cellular inflammatory response at the injury site and increasing the release of free radicals. An overabundance of free radicals contributes to tissue ischemia, cerebral edema, and disruption of the spine-blood barrier. The use of hypothermia (<35°C) as a therapeutic agent has been shown effective in providing neuroprotection from secondary injury [2]. Research has shown the benefits of hypothermia include decreasing oxygen consumption, free radical generation, neurotransmitter release, inflammation, and metabolic demands [3–5]. Even a temperature decrease of 1–2°C can be beneficial at the cellular level [4,6]. However, these studies use techniques that can be invasive. This research evaluates the effectiveness of using a non-invasive cooling pad on the torso to reduce the spinal cord temperature by at least 2°C.

In vivo experiments have been performed to test the effectiveness of a torso-cooling pad to reduce the temperature in the spinal cord and brain in rats. Coolant was circulated through the cooling pad to provide either mild or moderate cooling. Temperatures in the brain tissue, on the head surface, and on the spine and back surfaces were measured. During mild cooling, the temperature on the back surface was 22.82 +/- 2.43 degrees C compared to 29.34 +/- 1.94 degrees C on the spine surface. The temperature on the back surface during moderate cooling was 13.66 +/- 1.28 degrees C compared to 24.12 +/- 5.7 degrees C on the spine surface. Although the temperature in the brain tissue did not drastically deviate from its baseline value during cooling, there was a difference between the rectal and brain temperatures during cooling, which suggests mild hypothermia in the brain tissue. Using experimental data, theoretical models of the rat head and torso were developed to predict the regional temperatures and to validate the rat models. There was good agreement between the theoretical and experimental temperatures in the torso region. Differences between the predicted and measured temperatures in the brain are likely to be the result of imperfect mixing between the cold spinal fluid and the warm cerebrospinal fluid that surrounds the brain.

The Pennes bioheat equation and finite element method (FEM) are used to solve for the temperature distributions in the spinal cord and cerebrospinal fluid (CSF) during 30 min of cooling for spinal cord injury (SCI) patients. The average CSF and spinal cord temperatures are reduced by 3.48 and 2.72 degrees C, respectively. The 100-mm wide pad provides the desired cooling and uses the least amount of material. The presence of zero-average CSF oscillation under normal conditions decreases the cooling extent in the spinal cord due to the introduction of warm CSF surrounding the spinal cord. The temperature decrease in the spinal cord is more than doubled when the temperature at the back of the torso is lowered from 20 to 0 degrees C. Spinal cord ischemia, often observed after traumatic spinal cord injury, promotes cooling penetration. The proposed technique can reduce the spinal cord temperature by 2 degrees C within 30 min and may be a feasible treatment for traumatic SCI.

Traumatic injury causes mechanical tissue disruption that immediately follows a traumatic event. After the initial event, secondary injury often occurs. It is a cellular and molecular response to external trauma, including ischemia, inflammation, apoptosis, necrosis, and edema in the central nervous system (CNS). Since secondary injuries can lead to paralysis and permanent neurological damage, most current treatment are devoted to delaying or preventing secondary neurological injury.