American journal of physiology. Lung cellular and molecular physiology
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Am. J. Physiol. Lung Cell Mol. Physiol. · Aug 2011
Diaphragm muscle fiber function and structure in humans with hemidiaphragm paralysis.
Recent studies proposed that mechanical inactivity of the human diaphragm during mechanical ventilation rapidly causes diaphragm atrophy and weakness. However, conclusive evidence for the notion that diaphragm weakness is a direct consequence of mechanical inactivity is lacking. To study the effect of hemidiaphragm paralysis on diaphragm muscle fiber function and structure in humans, biopsies were obtained from the paralyzed hemidiaphragm in eight patients with hemidiaphragm paralysis. ⋯ The cross-sectional area of slow fibers was reduced after 2 wk of paralysis; that of fast fibers was preserved up to 8 wk. The expression of the E3 ligases MAFbx and MuRF-1 and proteasome activity was not significantly upregulated in diaphragm fibers following paralysis, not even after 72 and 88 wk of paralysis, at which time marked atrophy of slow and fast diaphragm fibers had occurred. Diaphragm muscle fiber atrophy and weakness following hemidiaphragm paralysis develops slowly and takes months to occur.