Impaired Muscle Metabolic Function in a Mitochondrial Myopathy Patient

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0098 PURPOSE: Mitochondrial myopathy (MM) is a metabolic disorder, which may impair functional capacity during exercise and limit daily activity. We examined metabolic function in a 25-year old female patient with a possible mitochondrial disorder and an age matched healthy subject using simultaneous near infrared spectroscopy (NIRS) and 31P magnetic resonance spectroscopy (MRS) measures. METHODS: The MM patient and the healthy subject performed 12-second all out dynamic plantar flexion exercise and submaximal steady state (SS) plantar flexion exercise in a 2 Tesla, 75 cm bore MRS magnet. In both exercise protocols, subjects stopped the exercise when the medial gastrocnemius muscle phosphocreatine (PCr) level declined to 50% of the resting PCr. Muscle deoxygenation, reoxygenation, PCr, inorganic phosphate (Pi), ATP, and muscle pH during exercise and recovery were calculated from NIRS and MRS spectra. RESULTS: Compared to the healthy subject, the MM patient exhibited much slower rates of reoxygenation (T50: 15 s vs. 230 s) and PCr resynthesis (KPCr = 2.10 min−1 vs. 1.20 min−1) after 12-second exercise. At the onset of SS exercise, the MM patient showed much faster PCr breakdown (dPCr/dt: −4.12 %/s vs. −1.13 %/s) while Hb/Mb-deoxygenation was minimal compared to the healthy subject. In addition, the MM patient reached 50% of her resting PCr much faster than the healthy subject during steady state exercise protocol (1.5 minutes vs. 5 minutes). CONCLUSIONS: The nominal deoxygenation and faster PCr breakdown during exercise and the nominal reoxygenation and slower PCr resynthesis rates during recovery for the MM patient, indicate impaired mitochondrial oxidative capacity. These results suggest that NIRS may provide a reliable and relatively inexpensive means of assessing mitochondrial myopathies compared to MRS. Supported by NIH HL 44125