Figure 2.

Maintained mitochondrial respiration in diaphragm muscle fibers. (A) Example of experimental recording of mitochondrial respiration in diaphragm muscle fibers. (Top) Oxygen concentration, which was maintained above 300 μM to avoid limitations in oxygen supply. (Bottom) Oxygen consumption per milligram wet weight muscle mass. Leak respiration is a measure of oxygen flux compensating for proton leakage from the intermembranous space through the inner membrane to the matrix. Maximal complex I–stimulated respiration is measured after addition of glutamate, malate and pyruvate, and ADP. Maximal uncoupled respiration is measured after adding succinate and FCCP [carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone] to dissipate the mitochondrial membrane potential. Uncoupled complex II–stimulated respiration is the oxygen consumption of complex II by blocking complex I with rotenone. No differences were observed in (B) leak respiration, (C) complex I–stimulated respiration, (D) maximal uncoupled respiration, and (E) uncoupled complex II–stimulated respiration between critically ill patients and control patients. Each data point represents the mean of two mitochondrial respiration measurements in a diaphragm biopsy of one patient. Data in B–E are presented as median and interquartile range. CI = complex I; CII = complex II; Crit. ill = critically ill; NS = not significant.