Diagnostic yield of the lactate stress test in respiratory chain disorders under absolute and relative workload.
Usually, the lactate stress test is carried under a constant, low workload maintained for 15 min, although there are indications that the lactate response to exercise is a function of the relative workload, and that a workload for only 5 min does not decrease its sensitivity. Thus, this study compared the diagnostic yield of the lactate stress test when carried out under a constant workload of 30 W (LSTA) and under a workload of 30% of maximum (LSTR), and when the workload was maintained for 5 and 15 min. In 16 patients with respiratory chain disorders, 12 women, four men, aged 27--88 years, the LSTA and LSTR were carried out on 2 different days, within 48 h. For both tests serum lactate was determined before, during and after a 15-min workload on a bicycle. Upper reference limits at rest, 5, 10, 15 min after starting, and 15 min after finishing the exercise were 1.9, 2.0, 2.0, 2.0, and 1.6 mmol/l for the LSTA, and 2.3, 3.0, 3.2, 3.4 and 2.7 mmol/l for the LSTR. The sensitivity was 88% for the LSTA and 63% for the LSTR. The specificity of the LSTA was 94%. The diagnostic yield of both tests was similar when the workload was maintained for 5 or 15 min. In conclusion, the LSTA should be preferred to the LSTR. Three lactate determinations during 15 min have no advantage over a single lactate determination after a 5 min workload of 30 W.
Finsterer
J
J
Ludwig Boltzmann Institute for Research in Neuromuscular Disorders, Postfach 348, 1180 Vienna, Austria. fij@2nr.nkr.magiwien.gv.at
Milvay
E
E
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004579:Electron Transport / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000032:analysis* / Q000097:blood*; D008297:Male; D008875:Middle Aged; D017240:Mitochondrial Myopathies / Q000097:blood* / Q000175:diagnosis* / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology; D016526:Workload
D019344:Lactic Acid