Mechanical ventilation can weaken lung muscles in as little as 18 hours of use, according to a new study that helps explain why weaning some patients from a ventilator is so difficult. The results suggest that the practice of providing ventilator support to "rest" a patient's respiratory muscles may encourage atrophy of the diaphragm and be counterproductive.

Researchers analyzed diaphragm biopsy specimens from 14 patients who were brain-dead and who'd been on a ventilator for 18 to 69 hours, and from 8 surgical patients who'd been on a ventilator for no more than 3 hours. They found that patients who'd been on a ventilator for longer periods had atrophy of diaphragm myofibers.

Researchers say their findings are consistent with increased breakdown of diaphragmatic proteins (proteolysis) during inactivity. They speculate that blocking or attenuating diaphragm proteolytic pathways in patients on ventilators might reduce problems with weaning.

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