"Ischemia reperfusion injury" is the medical term for injuries that stem from the renewed flow of blood through injured and healing tissue. It often affects patients who received traumatic injuries or underwent surgeries, as well as soldiers who got wounded on the battlefield.
A University of Virginia (UVA) research team led by Dr. Zhen Yan were determined to come up with an effective means of reducing blood flow-related injuries for these patients. Yan specialized in the cellular benefits of physical exercise. He reported that working out before the injury-causing event made it much less likely for muscles and nerves to sustain additional physical damage.
"Exercise-trained mice had a much better recovery, evidenced by less nerve damage, less muscle damage and less reduction of contractile function [in the muscle] immediately after injury and days later," Yan explained. (Related: 6 Months of aerobic exercise can improve neurocognition among older people, says study.)
First responders and first aid providers sometimes need to keep a victim from bleeding out. Many use a tourniquet to halt blood circulation until the patient reaches the emergency room and receives replacement blood.
However, stopping blood flow makes ischemia reperfusion injuries all the more likely. To prevent blood flow from causing further damage to already-injured wounds, circulation should only be cut off for a maximum of 90 minutes.
In order to evaluate the effects of reperfusion injury on both muscles and nerves, the UVA researchers created a mouse model. Mice were allowed to exercise in the form of voluntary running. Then they were subjected to surgical operations.
Furthermore, the researchers evaluated the level of oxidative stress experienced by the mitochondria of the cells once blood began flowing through the area again.
They found that mice that did physical exercises before their injury displayed reduced levels of damage from ischemia reperfusion. Pre-injury workouts strengthened the muscles and nerves, which protected the cells from getting damaged by restored blood flow. However, exercise did not reduce the amount of oxidative stress experienced by the tissues.
An earlier study by Yan examined the activity of muscle cells during the loss and restoration of blood flow. He compared the cells to circuit boards that were normally hooked up to wires but could get disconnected.
In that experiment, he treated the mice with a compound that protected the mitochondria of muscle cells from harm. Specifically, it shielded a structure called a neuromuscular junction, where the muscle and the nerve are physically linked in order to regulate the contraction of the muscle.
The compound protected the neuromuscular junction from taking any damage. In the future, a refined version could be adapted for emergency medical use by humans.
"On the battlefield, a simple thing to do is to put a bandage around the limb to block the circulation, to block the bleeding," Yan explained in a press release. "But at a certain point, you have to re-establish circulation, and our approach could offer a way to minimize the collateral damage and get better outcomes."
It appeared that physical exercise achieves the same protective effect as the compound. However, exercise used a different means of protecting the neuromuscular junction from getting damaged by ischemia reperfusion.