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Mixed venous CO2 tension during exercise.

J H Auchincloss, R Gilbert, M Kuppinger

    Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology
    |June 1, 1980
    PubMed
    Summary
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    The Collier method for estimating CO2 tension is more reliable than the Defares method during exercise tests. This finding is crucial for accurately assessing cardiac output in both healthy individuals and those with coronary artery disease.

    Area of Science:

    • Physiology
    • Cardiovascular Research
    • Pulmonary Function Testing

    Background:

    • Accurate estimation of mixed venous CO2 tension is vital for assessing cardiac output.
    • Two common methods, the Defares (extrapolation) and Collier (equilibrium) CO2 rebreathing techniques, are used for this purpose.
    • Comparative analysis of these methods, particularly during exercise, is necessary to determine their clinical utility.

    Purpose of the Study:

    • To compare the Defares CO2 rebreathing method with the corrected Collier method for estimating mixed venous CO2 tension.
    • To evaluate the reliability and consistency of both methods in adult subjects, including those with coronary artery disease, during treadmill exercise.
    • To determine which method is superior for exercise evaluation of cardiac output.

    Main Methods:

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    • A total of 95 adult subjects (25 with coronary artery disease) participated in the study.
    • Mixed venous CO2 tension was measured using both the Defares and Collier CO2 rebreathing methods during treadmill exercise at 123 W.
    • Collier values were corrected for downstream effects, while Defares values remained uncorrected. Duplicate determinations and paired comparisons were performed.

    Main Results:

    • Both methods yielded similar mean values in normal subjects during 123 W treadmill exercise.
    • The Collier method demonstrated higher reliability with a coefficient of variation (CV) of 2.5% compared to the Defares method's CV of 4.5% in duplicate determinations.
    • Defares values showed variability, averaging higher or lower than Collier values based on technique and analysis, whereas Collier values were unaffected by rebreathing duration (10 vs. 15 s).

    Conclusions:

    • The corrected Collier CO2 rebreathing method is more reliable and consistent than the uncorrected Defares method for estimating mixed venous CO2 tension during exercise.
    • The Collier technique is recommended for exercise evaluation of cardiac output in both healthy and diseased subjects, particularly when aiming for specific workloads (82 or 123 W) in single test sessions.
    • The findings support the superiority of the Collier method for practical clinical application in exercise physiology assessments.