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Breathing Muscles Atrophy Quickly During Mechanical Ventilation

Finding could one day help ICU patients get off respirator faster, researcher says

WEDNESDAY, March 26, 2008 (HealthDay News) -- A study showing the rapid weakening of unused breathing muscles during mechanical respiration could lead to improved survival for people who are put on ventilators in intensive care units, researchers say.

"What we think our work does is open the possibility of pharmacologically blocking the signaling pathways that mediate atrophy of these fibers," said study author Dr. Sanford Levine, a professor of surgery at the University of Pennsylvania. He is the lead author of a report on the finding, published in the March 27 issue of the New England Journal of Medicine.

Levine and his colleagues looked at the microscopic condition of muscle fibers from the diaphragms of 14 brain-dead organ donors placed on mechanical ventilation for 18 hours or more and similar fibers from eight people who had mechanical ventilation for two to three hours because of lung surgery.

Earlier work in rats by another member of the research team, Scott K. Powers of the University of Florida, showed rapid breakdown of diaphragm muscle fibers during prolonged mechanical ventilation, Levine said. In the human studies, he said, "the results were pretty much what we saw in the animal studies, a 57 percent decrease in the cross-section of slow fibers, a 53 percent decrease in the fast fibers."

"We were quite amazed at the rapidity with which atrophy developed," Levine said.

About one-third of patients in intensive care are mechanically ventilated, with a machine generating a controlled flow of air to the respiratory system. There has been a running controversy about how much rest the diaphragm muscles should get, Levine said: "If you rest these muscles completely, are you going to get into trouble?"

At least one study has shown that periodically stopping mechanical ventilation, a "wake-up-and-breathe" protocol, improves results. The detailed results of the new study give molecular backing to that idea.

The findings also raise the possibility of blocking the pathways that cause muscle degeneration, Levine said. "There are more than one pathways, which probably are not completely separate," he said. "These pathways signal reactive oxygen species to set off this signaling. There could be pharmacological agents we could give to patients who go onto mechanical ventilation and hopefully have a major impact on getting them off the ventilator."

It is "quite an important study," said Gary C. Sieck, chairman of the department of physiology and biomedical engineering at the Mayo Clinic, and co-author of an accompanying editorial. "There have been studies in animals in the past," he said. "This is the first study to actually show in humans how sharply mechanical ventilation can lead to decrease in the strength of respiratory muscles."

In terms of medial practice, "this may call for a change, to get patients off mechanical ventilators as early as possible," Sieck said.

What the study shows is that too much inactivity can be bad for respiratory muscles, he said. "Resting these muscles could be comparable to bed rest for patients," he said. "You get weaker with bed rest. And astronauts in space come back with weakened muscles."

More information

Learn about mechanical ventilation from the American Thoracic Society.

SOURCES: Sanford Levine, M.D., professor, surgery, University of Pennsylvania, Philadelphia; Gary C. Sieck, Ph.D., chairman, department of physiology and biomechanical engineering, Mayo Clinic, Rochester, Minn.; March 27, 2008, New England Journal of Medicine
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