Impairment of muscular metabolism in chronic respiratory failure. A human 31 P MRS study

The calf muscle metabolism of 7 patients with stable chronic respiratory failure (PaO 2 below 65 Torr) was studied using 31 P NMR spectroscopy. NMR spectra were acquired at rest, during the course of 360 pedal movements at 20, 35 and 50% of the maximal voluntary contraction (MVC) and during recovery. Eight normal aged‐matched subjects served as a control group. In resting muscle, no significant differences were observed between both groups as regards intracellular pH, inorganic phosphate/phosphocreatine (P i /PCr) and β‐ATP/PCr + Pi + phosphomonoester (PME) ratios. Although effective power outputs were similar for both groups at each work level, patients exhibited a higher P i /PCr ratio than healthy controls (3.19 ± 1.01 vs 0.49 ± 0.05 at 50% MVC; p < 0.01) and a lower pH i (6.65 ± 0.11 vs 7.06 ± 0.02 at 50% MVC; p < 0.01). Moreover, PCr resynthesis during recovery was slower in patients than in control subjects ( t 1/2 PCr = 1.26 ± 0.30 vs 0.47 ± 0.05 min; p = 0.01). These results suggest impairment of aerobic capacity in a non‐ventilatory working muscle, probably due to hypoxemia in patients with chronic respiratory failure.