AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 5 673-R677, Copyright © 1983 by American Physiological Society
A bladder contractility constant
J. C. Byrne and A. Tozeren
Muscle contractility can be characterized by two related properties: force
and velocity. The initial velocity of a tetanic contraction is inversely
related to preload. This was demonstrated experimentally by Hill and
quantified in his well-known empiric equation. Subsequent investigators
argued that a theoretical maximum contractile element velocity (V max)
could be predicted from the rate of change of isometric force. V max has
been applied clinically in heart studies, prompting others to use similar
methods to evaluate bladder contractility. These attempts have so far been
unsuccessful. The present study shows for whole canine bladders that the
time to reach maximum isometric force from the moment of onset of active
contraction is a constant independent of muscle length, preload, and
maximum force. This can be expressed as a frequency constant (omega) whose
calculation appears similar to that for V max. In contrast to V max, omega
is obtained only from the active component of pressure.
