Effect of plasma volume loss during graded exercise testing on blood lactate concentration.
Previous studies have shown that plasma volume (PV) loss can be a confounding variable in the interpretation of changes in blood constituents. We examined the effect of PV loss on three features of the blood lactate versus work-rate relationship, namely, slight blood lactate increase during the early stages of graded exercise testing (GXT); work rate at the onset of a systematic increase in blood lactate, i.e., lactate threshold (LT); and work rate at a blood lactate concentration of 4 mM, i.e., onset of blood lactate accumulation (OBLA). Fourteen subjects underwent cycle ergometer GXT. Blood samples were obtained at rest and at the end of each 3-min work-rate increment and analyzed for hematocrit and lactate concentration. For exercise levels up to and including LT, PV loss was relatively stable at approximately 2.8%. Beyond LT, PV loss accelerated. From the first work rate to LT, blood lactate concentration uncorrected for PV loss increased 0.24 +/- 0.07 mM (P < 0.05). After correction for PV loss, the increase was 0.21 +/- 0.08 mM (P < 0.05). These mean increases were not significantly different from each other. For the four exercise levels above LT common to most subjects, PV-corrected lactate values were significantly lower than uncorrected values. Correction of lactate values for PV loss did not alter LT for any subject, but it did result in a significant increase in OBLA. Thus, PV loss has the potential to be a confounding variable for the interpretation of blood lactate parameters that are determined at exercise levels above LT.
Davis
James A
JA
Laboratory of Applied Physiology, Department of Kinesiology, California State University/Long Beach, Long Beach, CA 90840-4901, USA. jad@csulb.edu
Rozenek
Ralph
R
Decicco
Derek M
DM
Carizzi
Michael T
MT
Pham
Patrick H
PH
D000328:Adult; D019963:Clinical Chemistry Tests / Q000379:methods* / Q000592:standards; D005080:Exercise Test; D005260:Female; D006400:Hematocrit; D006801:Humans; D007773:Lactates / Q000032:analysis / Q000097:blood*; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D010953:Plasma Volume / Q000502:physiology*
D007773:Lactates