A STANDARDIZED BICYCLE ERGOMETER TEST IN THE DIAGNOSIS AND MONITORINGOF MITOCHONDRIAL MYOPATHIES

Exercise tests are widely used as simple, noninvasive screening method s in the differential diagnosis of metabolic myopathies. Exercise prot ocols have not been standardized with regard to duration of the test, workload, or monitored metabolic parameters. Potentially interfering p arameters such as gender or maximal isometric force of the individuals have not been investigated. Here we describe a standardized bicycle e rgometry protocol with a stepwise increasing workload between 30 and 1 00 watts.The Venous lactate/pyruvate (L/P) ratio proved to be the one clinically most useful parameter in the functional diagnosis of mitoch ondrial myopathies with pathological exercise Values in all nine exami ned patients.Additionally, the effects of coenzyme Q therapy in these patients were most clearly mirrored by changes in the L/P ratio. Nonsp ecifically elevated venous lactate concentrations above 5 mmol/l are r arely found in healthy female volunteers with low maximal isometric fo rce of the M. quadriceps femoris. Other parameters such as serum free fatty acids, ketone bodies, intermediate products of the Krebs cycle o r spirometric investigations add only little additional information.Th e exercise test described may be useful as an additional investigation in the differential diagnosis of metabolic myopathies.