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Re: Difficulty explaining VO2max

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  • Ian Shrier
    I think it is important that everyone remember that: Cardiac output = HR * stroke volume The ejection fraction is not in the equation. Stroke volume increases
    Message 1 of 4 , Mar 1, 2009
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      I think it is important that everyone remember that:

      Cardiac output = HR * stroke volume

      The ejection fraction is not in the equation.

      Stroke volume increases if there is an increase in end-systolic volume
      or a decrease in end-diastolic volume. The ejection fraction is simply
      a function of these.

      A normal heart has an ejection fraction above 60%. Ejection fractions
      lower than 60% mean the person is starting to have heart failure.
      Ejection fractions less than 50% are associated with increased
      mortality and ejection fractions less then 40% represent moderate to
      severe heart failure.

      If you start at 60% ejection fraction, it is impossible to double it
      to 120%. This is why Carl Foster said the most liberal estimate would
      be from 60% to 80%. Note that this is a 33% increase and not a 60%-80%
      increase as Catherine Bacon says below.

      And of course, there is the increased a-v extraction noted by previous
      answers.

      So, to keep it simple, the increase in VO2max comes partly from an
      increase in cardiac output (which comes because of a mix of an
      increase in stroke volume and HR), and an and partly from an increase
      in a-v extraction.


      Of course, we don't usually exercise at VO2max so the changes with
      exercise may be very different when exercising at VO2 max vs
      submaximal exercise. I went looking for a table at VO2max but couldn't
      get one online. Here is a table from a paper in JAP in 2009 in middle-
      aged men cycling at 60-65% of VO2max. Note that most of the increase
      in stroke volume does come from ejection fraction in this table, and
      cardiac output increases are therefore due to HR and "ejection-
      fraction related increases in stroke volume". At very high heart rates
      experienced at VO2max, there is less time for the heart to fill, end-
      systolic volume therefore decreases, and this leads to decreases in
      stroke volume (not sure if ejection fraction declines but I think so).
    • Foster Carl C
      The study I referenced earlier is listed below. There were other data contemporary with this, by Steven Rerych for Duke, that was substantially similar. I
      Message 2 of 4 , Mar 1, 2009
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        The study I referenced earlier is listed below.   There were other data contemporary with this, by Steven Rerych for Duke, that was substantially similar.  I think the citation was Annals of Surgery, but not sure without going to find it.

         

        To get a VO2 of 6L, assuming 15 gm% hgb concentration, you have an a-v O2 difference of 150 ml/L.

        Therefore in terms of the Fick equation

        VO2=CO*a-v O2difference

        6000=CO*150

        CO=40 L/min

        CO=HR*SV=HR*EDV*EF

        40000ml=200*EDV*0.8

        40000=EDV*160

        EDV=250 ml

        This is a big heart, but not out of the range of what is reported (or calculated ) from literature values.

        More than a generation ago, the Swedes used green dye and reported occasional CO values of 40 L/min in athletes.

         

        Assuming a resting VO2 of 300 ml/min, a HR of 50, an EF of 0.6 and an a-vO2 difference of 50 ml/L

        300=CO*50

        CO=6 L/min

        6000 ml/min = 50*0.6*EDV

        EDV=200 ml

         

        Thus, in terms of the original question

        HR*4

        avO2 difference *3

        EF*1.33

        EDV*1.25

        CO*4*1.33*1.25=6.65

        SV*1.66

         

        Reference

        AnholmJD, Foster C, Carpenter J, Pollock ML, Hellman CK, Schmidt DH:  Effect of habitual exercise on the left ventricular response to exercise.  J Appl Physiol 52: 1648-1651, 1982.

         

        Carl Foster

         

         


        From: sportscience@yahoogroups.com [mailto:sportscience@yahoogroups.com] On Behalf Of Ian Shrier
        Sent: Sunday, March 01, 2009 6:13 AM
        To: sportscience@yahoogroups.com
        Subject: Re: Difficulty explaining VO2max

         

        I think it is important that everyone remember that:

        Cardiac output = HR * stroke volume

        The ejection fraction is not in the equation.

        Stroke volume increases if there is an increase in end-systolic volume
        or a decrease in end-diastolic volume. The ejection fraction is simply
        a function of these.

        A normal heart has an ejection fraction above 60%. Ejection fractions
        lower than 60% mean the person is starting to have heart failure.
        Ejection fractions less than 50% are associated with increased
        mortality and ejection fractions less then 40% represent moderate to
        severe heart failure.

        If you start at 60% ejection fraction, it is impossible to double it
        to 120%. This is why Carl Foster said the most liberal estimate would
        be from 60% to 80%. Note that this is a 33% increase and not a 60%-80%
        increase as Catherine Bacon says below.

        And of course, there is the increased a-v extraction noted by previous
        answers.

        So, to keep it simple, the increase in VO2max comes partly from an
        increase in cardiac output (which comes because of a mix of an
        increase in stroke volume and HR), and an and partly from an increase
        in a-v extraction.

        Of course, we don't usually exercise at VO2max so the changes with
        exercise may be very different when exercising at VO2 max vs
        submaximal exercise. I went looking for a table at VO2max but couldn't
        get one online. Here is a table from a paper in JAP in 2009 in middle-
        aged men cycling at 60-65% of VO2max. Note that most of the increase
        in stroke volume does come from ejection fraction in this table, and
        cardiac output increases are therefore due to HR and "ejection-
        fraction related increases in stroke volume". At very high heart rates
        experienced at VO2max, there is less time for the heart to fill, end-
        systolic volume therefore decreases, and this leads to decreases in
        stroke volume (not sure if ejection fraction declines but I think so).

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