Cooling and rewarming for brain ischemia or injury: theoretical analysis.

A three-dimensional model is developed in this study to examine the transient and steady state temperature distribution in the brain during selective brain cooling (SBC) and subsequent rewarming. Selective brain cooling is induced through either wearing a cooling helmet or packing the head with ice. The ischemic region of the brain is simulated through reducing the blood perfusion rate to 20% of its normal value. The geometric and thermal properties and physiological characteristics for each layer, as well as the arterial blood temperature, are used as the input to the Pennes bioheat equation. Our data suggest that rapid cooling of the brain gray matter can be achieved by SBC on the head surface (26 min for adults versus 15 min for infants). Suboptimal thermal contact between the head surface and the coolant in most commercially available cooling helmets is suspected to be the main reason for delayed cooling in SBC as compared to the ice packing. The study has also demonstrated that the simulated 3 degrees C/h passive rewarming rate by exposing the head to room temperature after removing the source of cooling may be too rapid.