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Abstract
Background: The authors hypothesized that impaired oxygen extraction in mitochondrial myopathy (MM) results in a high oxygen saturation in venous effluent blood from working muscle and that this phenomenon can be used as a diagnostic tool for MM.
Methods: Twelve patients with MM, 10 patients with muscular dystrophy, and 12 healthy subjects were studied. All subjects performed intermittent static handgrip exercise (1/2 Hz) at 40% of maximal voluntary contraction (MVC) for 3 minutes. Cubital venous oxygen saturation and brachial artery flow were measured in the exercised arm.
Results: Exercise-induced venous oxygen desaturation was smaller in patients with MM (Δ − 7 ± 5%) than in subjects with muscular dystrophy (Δ − 38 ± 2%; p = 0.00001) and healthy subjects (Δ − 43 ± 2%; p = 0.0000002). MVC and exercise blood flow were similar in patients with MM (18 ± 3 kg; 436 ± 65 mL/min) and patients with muscular dystrophy (15 ± 3 kg; 460 ± 85 mL/min), but were higher in healthy subjects (32 ± 4 kg; 630 ± 58 mL/min; p < 0.03). In seven patients with MM and seven patients with McArdle disease, studied with a slightly different protocol, exercise-induced oxygen desaturation was also impaired in MM (Δ − ± 5%) compared with McArdle disease (Δ − 26 ± 3%; p = 0.007).
Conclusion: Oxygen desaturation in venous blood from exercising muscle is markedly lower in patients with mitochondrial myopathy than in subjects with other muscle diseases and healthy subjects, suggesting that a forearm exercise test can be a diagnostic screening tool for mitochondrial myopathy.
- Received September 6, 2001.
- Accepted February 15, 2002.
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