Impaired oxygen extraction in metabolic myopathies: detection and quantification by near-infrared spectroscopy.
Patients with mitochondrial myopathies (MM) or myophosphorylase deficiency (McArdle's disease, McA) show impaired capacity for O(2) extraction, low maximal aerobic power, and reduced exercise tolerance. Non-invasive tools are needed to quantify the metabolic impairment. Six patients with MM, 6 with McA, 25 with symptoms of metabolic myopathy but negative biopsy (patient-controls, P-CTRL) and 20 controls (CTRL) underwent an incremental cycloergometric test. Pulmonary O(2) uptake (VO(2)) and vastus lateralis oxygenation indices (by near-infrared spectroscopy, NIRS) were determined. Concentration changes of deoxygenated hemoglobin and myoglobin (Delta[deoxy(Hb + Mb)]) were considered an index of O(2) extraction. Delta[deoxy(Hb + Mb)] peak (percent limb ischemia) was lower in MM (25.3 +/- 12.0%) and McA (18.7 +/- 7.3) than in P-CTRL (62.4 +/- 3.9) and CTRL (71.3 +/- 3.9) subjects. VO(2) peak and Delta[deoxy(Hb + Mb)] peak were linearly related (r(2) = 0.83). In these patients, NIRS is a tool to detect and quantify non-invasively the metabolic impairment, which may be useful in the follow-up of patients and in the assessment of therapies and interventions.
Grassi
Bruno
B
Department of Science and Biomedical Technologies, University of Milan, LITA-Via Fratelli Cervi 93, I-20090 Segrate, MI, Italy. bruno.grassi@unimi.it
Marzorati
Mauro
M
Lanfranconi
Francesca
F
Ferri
Alessandra
A
Longaretti
Miriam
M
Stucchi
Andrea
A
Vago
Paola
P
Marconi
Claudio
C
Morandi
Lucia
L
D000328:Adult; D000368:Aged; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D006012:Glycogen Storage Disease Type V / Q000175:diagnosis* / Q000378:metabolism* / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D006454:Hemoglobins / Q000032:analysis / Q000378:metabolism; D006801:Humans; D008297:Male; D017240:Mitochondrial Myopathies / Q000175:diagnosis* / Q000378:metabolism* / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology; D009211:Myoglobin / Q000378:metabolism; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology; D011237:Predictive Value of Tests; D012016:Reference Values; D019265:Spectroscopy, Near-Infrared / Q000379:methods* / Q000639:trends
D006454:Hemoglobins; D009211:Myoglobin