Cardiac Hypertrophy Notes.TXT

Created : 2013-02-22
Revised : 2013-02-22
Author : Tom Coleman

Placing an additional load on the heart leads to increased
heart mass and contractile protein. The load can be either
continuous (aortic stenosis, regurg, hypertension) or
intermittent (athletic training).

Mechanisms are unknown, so I had to postulate a trophic
factor to connect load with protein dynamics.

Ventricle data from Scharhag.
                       Control Trained
                       ------- -------
V-O2-Max ((mL/Min)/kG)   42       68
LV/RV Mass              2.6      2.6
LV/RV EDV              0.99     1.05
LV/RV Stroke Volume    0.98     0.95

Left Ventricle
--------------
Mass (G)                148      200
EDV (mL)                125      167
Stroke Volume (mL)       74       99
Ejection Fraction (%)    59       59

Right Ventricle
---------------
Mass (G)                 56       77
EDV (mL)                128      160
Stroke Volume (mL)       79      102
Ejection Fraction (%)    62       63

One important take away here is that training induces
hypertrophy on both sides of the heart.

Some numbers for left ventricle mass (G) from Pluim.

                   Mass
                   ----
Control             174
Endurance Trained   249
Strength Trained    267
Combined Training   288

Mass in heart disease can go even higher. I looking for
suitable references.

Prolonged bed rest decreases ventricular mass. HumMod
starts up in a bed rest setting. Here are % decreases in
left ventricle mass with bedrest and spaceflight from
Dorfman (D), Perhonen (P) and Levine (L).

                        % Change
                        --------
Bed rest - 6 weeks (P)     -8%
Bed rest - 12 weeks (P)   -15.6%
Spaceflight (P)           -12%
Bed rest - 8.6 weeks (D)   -9%  (25% in RV)
Bed rest - 2 weeks (L)     -5%

So here is the proposed contractile protein multiplier.

                      Multiplier
                      ----------
Bed Rest                1.0
Normal Activity         1.1
Training                1.6
Severe Heart Disease    2.5

Persistance of Trophic Factor ===============================

Myocardial protein turns over on a regular basis. The trophic
factor increases anabolism. When the factor decreases,
anabolism decreases also. The process has a rather long
half-life, as suggested by the bed rest data above.

Coyle measured V-O2-Max is highly trained athletes as they
detrained. Of course, the decrease was due to both heart and
muscle factors, but it gives a hint.

          V-O2-Max (L/Min)
          ----------------
Trained     4.22
12 Days     3.93
21 Days     3.94
56 Days     3.67
84 Days     3.56

Morad measured the fall in left ventricle mass after aortic
valve replacement.

           LV Mass (G/M^2)   Estimate (G)
           ---------------  -------------
Immediate       174              313
1.6 Years       120              216
8.1 Years       105              189

With severe disease, there may be long-term structural
changes that are more fixed than training changes.

I think that I try a tau of 40 days.

Stimulus for Trophic Factor =================================

Fox argues that it is the intensity of training sessons that
improves V-O2-Max. Note that cardiac work will be 5 times
normal or above.

References ==================================================

Coyle, E.F. et.al. Time course of loss of adaptations after
stopping prolonged intense endurance training. J. Appl.
Physiol. 57(6):1857-1864, 1984.

Dorfman, T.A. et.al. Cardiac atrophy in women following bed
rest. J. Appl. Physiol. 103(1):8-16, 2007.

Fox, E.L. et.al. Frequency and duration of interval training
programs and changes in aerobic power. J. Appl. Physiol.
38(3):481-484, 1975.

Levine, B.D. et.al. Cardiac atrophy after bed-rest
deconditioning. Circulation 96:517-525, 1997.

Morad, E.S. et.at. Time course of regression of left
ventricular hypertrophy after aortic valve replacement.
Circulation 77(6):1345-1355, 1988.

Perhonen, M.A. et.al. Cardiac atrophy after bed rest and
spaceflight. J. Appl. Physiol. 91(2):645-653, 2001.

Pluim, B.M. et.al. The athlete's heart. A meta-analysis of
cardiac structure and function. Circulation 100:336-344, 1999.

Scharhag, J. et.al. Athlete's heart. Right and left ventricular
mass and function in male endurance athletes and untrained
individuals determined by magnetic resonance imaging.  J. Amer.
Coll. Cardiol. 40(10):1856-1863, 2002.

End