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Researchers at Texas Health Presbyterian Hospital Dallas Investigate Better Ways to Treat Soldiers Wounded in Combat|
DALLAS — Dallas researchers are investigating how the human body responds to bleeding in hot conditions, findings that could shape how wounded soldiers in Afghanistan are treated on the battlefield.
The researchers at the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital Dallas, led by Craig Crandall, Ph.D., one of the country’s foremost experts on thermoregulation, will present their findings at the conference of Advanced Technology Applications for Combat Casualty Care.
“What we’ve discovered suggests that when soldiers experience blood loss while heat-stressed, which is common in a combat environment, their capacity to maintain adequate blood pressure is greatly compromised,” said Crandall, who is director of the IEEM’s Thermoregulation Laboratory and a professor at UT Southwestern Medical Center. “That quickly leads to unconsciousness and other potentially life-threatening medical problems.” Crandall said that his team’s finding opens up the idea that cooling an otherwise hyperthermic soldier who is injured in combat might help them survive. IVs or oral intake of fluids could also be used to cool a patient’s body temperature.
“Soldiers are often heat-stressed prior to being injured,” he said. “So knowing how a higher-than-normal body temperature affects blood pressure when someone loses blood is very important.”
The findings could also impact how firefighters and police officers are treated after suffering an injury, Crandall said.
“Firefighters are often in high-heat environments when fighting structure fires,” he said. “But firefighters and police officers are also outside wearing their full uniforms and are at higher than average risk for an injury that could involve bleedings. Construction workers who are outside in the summer heat of North Texas also face the same perils if they’re injured on the job.”
In the study, 11 male subjects in their 20s were fitted with a tube-lined, water-perfused suit to elevate skin and internal temperatures. While their body temperatures were increased, researchers monitored their arterial blood pressure, cardiac output (how much blood the heart is pumping) and vascular resistance.
The purpose of the study was to test whether drops in blood pressure caused during a simulated hemorrhagic challenge while heat-stressed are the result of an inadequate increase in vascular resistance or cardiac output. The body’s blood vessels typically stiffen, like putting your finger over the edge of a hose, when the person loses blood to compensate for less blood volume. That increases blood pressure and helps ensure blood and its vital nutrients get to the brain and other organs.
Whether the loss of blood pressure was due to this lack of vessel stiffening or a reduction in cardiac output because of the injury has not been known until now.
“Our results strongly suggest that when someone experiences blood loss while heat stressed, his or her ability to maintain a safe level of blood pressure is severely compromised due to inadequate increases in systemic vascular resistance, or stiffening of the vessels,” Crandall said.
“It is very interesting to observe how powerful the need to regulate body temperature is for humans,” said Dr. Benjamin D. Levine, professor of medicine and cardiology at UT Southwestern and director of the IEEM. “Even when bleeding causes a critical shortage of blood, there is an over-riding demand to send blood to the skin to keep the body cool. We have seen this compromise not only in young healthy individuals, but also patients with other limitations in cardiac function, such as those with heart failure.”
Levine added: “This may be why cardiac patients are the most susceptible to injury during heat waves like the one we are experiencing now. This new work by Dr. Crandall counters prevailing wisdom in some emergency medicine circles that a patient in shock should be ‘kept warm.’ Perhaps strategies to cool them quickly would be more appropriate.”
Other authors of the paper were Morten Overgaard, Thomas Seifert and Niels Secher of the University of Copenhagen in Denmark.
The study was funded by the National Institutes of Health.
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