Journal of Applied Physiology, Vol 41, Issue 3 316-322, Copyright © 1976 by American Physiological Society
Uterine work in parturition
T. J. Kriewall
This paper presents a theoretical analysis relating work expended by the
uterus to the synergistic relationship between intrauterine pressure (IUP)
and cervical dilatation (CD). By utilizing a geometrical model for the
fetal presenting part which is assumed to be in contact with the cervix,
the changes in internal volume of the uterus with each contraction can be
shown to be functionally related to cervical dilatation. Thus work,
expressed in terms of foot-pounds, can be calculated using the integral of
pressure times incremental volume. By simulating intrauterine pressure and
cervical dilatation with continuous analytical wave forms, the alterations
required in uterine work to dilate the cervix are calculated for various
wave-form aberrations which are seen in clinical situations. The wave-form
aberrations are applied to an elastic cervical model as well as a
viscoelastic model. Using the principles of thermodynamics the areas of the
fetouterine complex which absorb the work generated by the contractions are
defined. It is shown that the efficiency of the contractions to dilate the
cervix can be calculated by evaluating the work expended in these various
areas of energy absorption. The purpose of this paper is to present the
theory upon which clinical findings in obstetrics can be based so that
conclusions drawn will be technically sound.
