| Developing a targeted cooling approach to quickly induce brain hypothermia while avoiding systemic complications is a challenge facing engineers and clinicians, even if the neuroprotective benefits of brain hypothermia have been demonstrated by animal studies and clinical trials. In this research, a theoretical and experimental approach is conducted to investigate the temperature distributions in the neck and brain for selectively cooling the arterial blood with a newly developed interstitial cooling device. In the theoretical simulation, a combination of vascular model and continuum model is developed to simulate the temperature fields in both the neck and brain regions. Brain hypothermia is induced by inserting a cooling device in the neck muscle and placing it on the common carotid artery to cool the arterial blood supplied to the brain. Parametric studies are conducted to test the sensitivity of various factors on the temperature distribution. It has shown that the length of the device, temperature of the device, and the tissue gap between the device and the blood vessel are the dominant factors that determine the effectiveness of this cooling approach. Under the current design parameters, the device is capable of inducing a temperature drop of 2.75°C along the common carotid artery and it results in a total of 88 W of heat carried away from the arterial blood. Temperature reduction in the brain tissue is almost uniform and up to 3.1°C temperature drop is achieved within one hour. Although the degree of the cooling in the arterial blood is inversely proportional to the blood flow rate of the arteries, the total heat loss from the arterial blood does not vary significantly if the blood flow rate changes during the cooling. Brain hypothermia can be achieved within one hour under the current design. In the in vivo experimental study, the developed cooling device is applied to an animal model to test its performance in a biological environment. Coolant is circulating inside the cooling device to achieve either mild or moderate cooling in the neck and brain tissue. For the mild cooling (cooling device surface temperature is 18.7 +/- 4.5°C), the temperature reductions are 2.16 +/- 0.63°C, 2.09 +/- 0.60°C, 1.87 +/- 0.59°C and 1.58 +/- 0.88°C at sites of brain-5 mm, brain-2 mm, skull, and scalp, respectively. After the surface temperature of the cooling device is further decreased to 12.8 +/- 2.8°C (moderate cooling), the temperature reduction in the head increases more than 85% to 3.69 +/- 3.21°C, 3.68 +/- 2.99°C, 3.34 +/- 2.50°C and 2.51 +/- 1.02°C, respectively. The experimental results are later used to validate the theoretical model. Our theoretically predicted brain temperatures show a good agreement with the experiment data. The current study helps understand heat transfer in tissue during cooling. It also lays the foundation for developing a reliable cooling device and a cooling system to be implemented in large animal studies and future clinic trials in applications such as stroke, head injury, open heart and neck surgeries, etc. |
