Body shuts down
As the body cools, the metabolism slows, reducing the need for oxygen. Limited blood circulation is directed to vital organs, including the brain, heart and kidneys, but not to non-vital organs such as the muscles, skin and periphery.
When hypothermia victims arrive in the emergency room, they are unresponsive and may have only one or two respirations per minute, compared to the 10-15 per minute that is normal. Doctors often cannot even detect a peripheral pulse to determine whether the heart is beating, Tveita said. In fact, victims of hypothermia may appear to be dead, even when they are not.
Understanding the body's physiological response to hypothermia became a popular research topic 40 years ago, when doctors wanted to use hypothermia during heart surgery. In fact, doctors did learn to use hypothermia to reduce oxygen consumption, to induce cardiac standstill and to restart the heart by rewarming, Tveita noted.
But research on hypothermia dropped off markedly after the surgical application was established. However, deaths from accidental hypothermia continue, and not just in the coldest climes. Tveita recalled the recent case of a person in a warmer climate who became hypothermic after being swept out to sea on a cold current.
Rats serve as model
"In this study, we wanted to find out if there are problems with low blood pressure, low pulse, low cardiac output (the volume of blood the heart can pump per minute), or with oxygen transport to the cells," Tveita said. In particular, the research team wanted to know if insufficient circulation leads to inadequate oxygen supply to the heart cells, which in turn leads to heart failure.
The researchers divided anesthetized rats into three groups: two hypothermic groups and a control group. They exposed one
Source:American Physiological Society