Current Technology Unlikely to Help

Graphic of blood flow in brain

Many ongoing clinical trials try to reduce brain temperatures through cooling units incorporated into hats or other devices that surround the head. However, the new findings suggest in most patients such techniques will be unable to defeat the natural temperature regulation built into the brain via the blood system.

Scientists at Washington University School of Medicine in St. Louis used rats to validate a "cold shielding" effect of blood flow that they previously predicted theoretically. The shielding effect, created by large quantities of warm blood that continually perfuse brain tissue, prevents a drop in temperatures around the head from penetrating beyond a certain depth in the brain.

"In adult humans, the characteristic length that this kind of cold assault appears to penetrate is approximately a tenth of an inch, leaving the temperature of approximately 6 inches of brain tissue unchanged," says senior author Dmitriy Yablonskiy, Ph.D., professor of radiology at the School of Medicine and of physics in Arts and Sciences.

The amount of blood flowing through brain tissue determines the extent of the shielding effect. Young children, infants and in particular newborns have smaller brains with lower blood flow and may be more susceptible to a cooling unit around the head. But for other patients, Yablonskiy asserts, a different approach is needed.

"Now that we know our theory is valid, we can use what we know about blood flow in various types of patients, calculate the characteristic length of this cold shield and make predictions on what the temperature distribution in the brain will be like," Yablonskiy says.

Yablonskiy notes that other approaches to induce hypothermia currently under consideration include cooling the entire body all at once and inserting cooling devices into the arteries that supply the brain with blood.; Source: Washington University School of Medicine