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  • Title: The effect of progressive exercise on the equilibrium rebreathing cardiac output method.
    Author: Auchincloss JH, Gilbert R, Morales R, Peppi D.
    Journal: Med Sci Sports Exerc; 1991 Sep; 23(9):1111-5. PubMed ID: 1943634.
    Abstract:
    The equilibrium CO2 rebreathing method has been used in the study of exercise cardiac output (Q) in health and disease, but the requirement for a steady state has usually limited its application to step function exercise. This limits testing to only a few levels of exertion in a laboratory session. We have devised a treadmill test where the grade is flat at the beginning and rises continuously at 1%.min-1 after stable measurements are obtained during level walking. The walking speed is determined by the subject's comfort and tolerance for fast walking. In series I seven normal subjects were studied with this protocol, and an automated system was employed for estimation of Q and oxygen uptake (VO2). For comparison of steady state and progressive tests, an interpolation method was devised which furnished a value of Q (progressive) that could exist at the value of VO2 obtained during the steady state. The average difference in Q so estimated between the steady state and the unsteady state was 0.3 l.min-1, SD = 1.7. This difference was less than the difference between averages of duplicate values of Q obtained during the steady state (1.11.min-1, SD = 16), and the difference between the two differences was not significant. Based on 51 determinations of Q and VO2 in eight normal subjects the unsteady state procedure furnished an average value of the relation slope of delta Q/delta VO2(-1) of 4.8 l.l-1. We conclude that the equilibrium CO2 method can be used to depict the Q, VO2 relationship over the range of VO2 at which rebreathing is tolerable.
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