A forearm exercise screening test for mitochondrial myopathy.
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 (Delta - 7 +/- 5%) than in subjects with muscular dystrophy (Delta - 38 +/- 2%; p = 0.00001) and healthy subjects (Delta - 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 (Delta - +/- 5%) compared with McArdle disease (Delta - 26 +/- 3%; p = 0.007).


CONCLUSIONS
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.
Jensen
Tina D
TD
Copenhagen Muscle Research Center, Department of Neurology, National University Hospital, Rigshospitalet, Copenhagen, Denmark.
Kazemi-Esfarjani
Pedram
P
Skomorowska
Elwira
E
Vissing
John
J
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D005080:Exercise Test / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D005542:Forearm; D006012:Glycogen Storage Disease Type V / Q000175:diagnosis / Q000503:physiopathology; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D017240:Mitochondrial Myopathies / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology; D009136:Muscular Dystrophies / Q000175:diagnosis / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology
D019344:Lactic Acid