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  • Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology
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Reliability of the cardiac output measurement with the indirect Fick-principle for CO2 during exercise

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Cardiac output measurements were performed during 50 exercise tests in 16 normal subjects employing the indirect Fick principle for CO2. During sub-maximal steady state exercise the plateau CO2 tension (\(P_{plat CO_2 } \)) was estimated with a rebreathing procedure. The mixed venous CO2 tension (\(P_{\bar v CO_2 } \)) was calculated by subtracting the alveolocapillary CO2 tension difference from the\(P_{plat CO_2 } \). Compared with data from the literature the most valid calculation of the cardiac output was obtained by using the\(P_{\bar v CO_2 } \). Cardiac output values, calculated via the\(P_{plat CO_2 } \) turned out to be too low.

The reproducibility was tested by repitition of 18 exercise tests at least after 5 days. The relative standard error of a single observation was 4.1% for the cardiac output, which was found to be as good as that of invasive measurements.

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van Herwaarden, C.L.A., Binkhorst, R.A., Fennis, J.F.M. et al. Reliability of the cardiac output measurement with the indirect Fick-principle for CO2 during exercise. Pflügers Arch. 385, 21–23 (1980). https://doi.org/10.1007/BF00583910

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Key words

  • Cardiac output
  • CO2 rebreathing
  • Exercise