Breathing Muscles Atrophy Quickly During Mechanical Ventilation

By Ed Edelson
HealthDay Reporter
Thursday, March 27, 2008; 4:00 AM

Copyright © 2008 ScoutNews, LLC. All rights reserved.

WEDNESDAY, March 26 (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."