Role of cardiopulmonary exercise test in patients with mitochondrial myopathies

BACKGROUND: Exercise tests has been used in the diagnosis of metabolic myop athies. If there is an anormal response pattern in mild mitochondrial myopa thy (MM) and her role in the initial suspect diagnostic is unknown, SUBJECTS AND METHODS: Prospective study of 26 patients with mitochondrial m yopathy (15 men, 11 women) and a control group of 14 sedentary volunteers ( 9 men, 5 woman) with similar antropometric characteristics. We have maked p ulmonary function tests and treadmill exercise with serial venous sampling of blood lactate, piruvate, ketone bodies, free fatty acids and creatinkina se. RESULTS: Patients with MM showed exercise limitation with lower maximal pow er (MM = 143 [47] vatts, C = 187 [40] vatts, p = 0.006), maximal oxygen upt ake (MM = 27 [8] ml/min/kg, C = 40 [7] ml/min/kg, p = 0.001) and maximal ox ygen pulse (MM = 11 [3] ml/beat, C = 14 [3] ml/beat, p = 0.006). For the sa me oxygen uptake the heart rate was higher and the anaerobic threshold was earlier in MM patients (MM = 48% [14], C = 62% [12], p = 0.01). We found a considerable slower maximal oxygen uptake in patients with lipid increase i n muscle biopsy (n = 15). Acetoacetate curves, beta-hydroxybutirate, free f atty acids and creatinkinase were similar in both groups. The exercise test was pathologic in 17/26 of the patients. The sensitivity of the exercise t est for maximal oxygen uptake was 0.65. CONCLUSIONS: The cardiopulmonary exercise test is a useful test in the susp ect initial diagnostic of patients with mild mitochondrial myopathy because the majority of patients show a pathologic test.