In Vivo Magnetic Resonance Spectroscopy

Background Skeletal muscle metabolic abnormalities have been described in patients with heart failure that are independent of total limb perfusion, histochemical changes, and muscle mass. However, these skeletal muscle metabolic abnormalities may result from tissue hypoxia caused by maldistribution of flow. Myoglobin is an 02 binding protein that can indirectly assess tissue hypoxia. Methods and Results In vivo measurement of deoxymyoglobin was performed by use of proton ('H) magnetic resonance spectroscopy in 16 heart failure (HF) (left ventricular ejection fraction=20±6%; Vo2=14.5±5.1 mL/kg per minute) and 7 healthy (Nl) subjects. Simultaneous phosphorus ("P) magnetic resonance spectroscopy and near-infrared spectroscopy also were obtained to examine muscle metabolism and oxygenation. Supine calf plantarflexion was performed every 4 seconds. Incremental steady-state work was performed. A second exercise protocol studied rapid incremental (RAMP) exercise with plantarflexion every 2 seconds. Arterial occlusion at end exercise provided physiological calibration for myoglobin and hemoglobin signals. With steady-state exercise, the work slope, ie, inorganic phosphorus to phosphocreatine ratios versus work, was significantly greater in patients with heart failure (Nl: 0.18±0.08; HF: 0.40±0.32 W-'; P<.05). Intracellular pH was reduced