Exercise can protect both muscle and nerves from damage caused by the restoration of blood flow after injury or surgery, a study has found. Researchers from the University of Virginia (UVA) in the US are working to better understand how the body is damaged by the restoration of blood flow -- known as ischemia-reperfusion injury.
They are also trying to find ways to improve outcomes for people who suffer it, including surgery and trauma patients and soldiers injured on the battlefield. The new finding, published in the Journal of Applied Physiology. shows that pre-injury exercise has substantial benefits in terms of preserving both muscle and nerve.
"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," said Zhen Yan, the director of the Center for Skeletal Muscle Research at UVA.
Because of the damage caused by reperfusion injury, doctors now seek to limit the amount of time blood flow is cut off to no more than 90 minutes. "There are some situations where you have to stop bleeding to save life," Yan said.
"The way we often do that is by putting on a tourniquet, to completely stop the circulation until the patient can be taken to the emergency room. But there's an issue there. We cannot block it too long. The tissues will be dead. We have to restore the blood flow at some point, but it will cause reperfusion injury. There is a conundrum," he said.
The team developed a "reporter gene" called the MitoTimer to understand the effects of reperfusion injury on muscle and nerves. The reporter gene allowed them to measure the amount of "oxidative stress" to the cells' power plants, mitochondria when blood flow was restored.
The researchers found that pre-injury exercise clearly reduced the damage to both muscle and nerve, but it did not significantly reduce the amount of oxidative stress. "We know exercise made the muscle and nerve tougher. The protection is very clear," Yan said.
While the mechanism for that protection is not yet understood, Yan's previous research has shed light on what happens to muscle cells when blood flow is restored.
He likens it to wires being disconnected from a circuit board. He has even identified a compound that, in mice, helps protect the mitochondria in those circuit boards. "With this treatment, we found the circuit board, a structure called neuromuscular junction where the nerve is physically connected with muscle for control of its contraction, was preserved," Yan said.
"The wires remained connected. The function is normal. Therefore, recovery is much faster," he said. This drug could potentially prevent nerve damage caused by the restoration of blood flow and speed patients' recovery, researchers said.
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