AJP - Heart and Circulatory Physiology, Vol 234, Issue 1 88-H93, Copyright © 1978 by American Physiological Society
Contractile state of hypertrophied left ventricle in long-standing volume overload
W. H. Newman
The purpose of this investigation was to evaluate the contribution of
hypertrophy, the length-tension phenomenon, and inotropism to adaptation of
the left ventricle (LV) to volume overload of up to 3 yr duration. Overload
was produced in dogs by heart block, and contractile state was evaluated
with a Walton-Brodie arch. Recording of contractile force (CF) in grams vs.
muscle length from the LV indicated that dogs with hypertrophy were
functioning at a higher point on the ascending limb of the length-tension
curve than normals (76 percent Lmax in hypertrophy vs. 61 percent Lmax in
normal). Additionally, in hypertrophy, all points on the length-tension
curve above 80 percent Lmax were significantly elevated. None of these
changes were seen in dogs in which block was induced on the day of the
experiment. When CF was normalized for hypertrophy and expressed as CF/cm2,
the length-tension curves were practically superimposable. These data
suggest that adaptation was accomplished by hypertrophy, a shift up the
length-tension curve without a depression of inotropic state.
