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The\(\dot VCO_2 \)/\(\dot VO_2 \) relationship during heavy, constant work rate exercise reflects the rate of lactic acid accumulation

  • William Stringier
  • Karlman Wasserman
  • Richard Casaburi
Original Article

Abstract

Oxygen uptake (\(\dot VO_2 \)) kinetics have been reported to be modified when lactic acid accumulates; however little attention has been given to the simultaneous carbon dioxide production (\(\dot VCO_2 \)>) kinetics. To demonstrate how\(\dot VCO_2 \) changes as a function of\(\dot VO_2 \) when lactic acid is buffered by bicarbonate, eight healthy subjects performed 6-min constant work rate cycle ergometer exercise tests at moderate, heavy and very heavy exercise intensities.\(\dot VCO_2 \) and\(\dot VO_2 \) were measured breath-by-breath, and arterial blood samples were obtained every 7.5 s during the first 3 min of exercise, and were analyzed for pH, partial pressure of carbon dioxide, standard bicarbonate, and lactate.\(\dot VCO_2 \) abruptly increased relative to\(\dot VO_2 \) between 40 and 50 s after the start of exercise for the high exercise intensities. These gas exchange events were observed to correlate well with the time and\(\dot VO_2 \) at which lactic acid increased and plasma bicarbonate decreased (r = 0.90,r = 0.95, respectively). We conclude that bicarbonate buffering of lactic acid can be determined from the acceleration of\(\dot VCO_2 \) relative to\(\dot VO_2 \) kinetics in response to constant work rate exercise and the increase is quantitatively related to the magnitude of the lactic acid increase. This is easily visualized from a plot of\(\dot VCO_2 \) as a function of\(\dot VO_2 \).

Key words

Oxygen uptake kinetics Carbon dioxide output kinetics Lactate Standard bicarbonate Arterial blood gases 

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • William Stringier
    • 1
  • Karlman Wasserman
    • 1
  • Richard Casaburi
    • 1
  1. 1.Division of Respiratory and Critical Care, Physiology and MedicineHarbor-UCLA Medical CenterTorranceUSA

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