Speed and pressure characteristics of external anal sphincter
contractions.
Herdmann, J[diaeresis]org, Paul Enck, Paola Zacchi-Deutschbein, Ursula
Ostermann.
Department of Neurosurgery and Department of Gastroenterology,
Heinrich-Heine-University, D[umlaut]usseldorf, Germany
APStracts 2:0075G, 1995.
The principle of isochronism reflects constant contraction time for
varying strengths of muscle contraction. This principle was studied
for the innervation of the pelvic floor in humans using motor evoked
potentials (MEPs) and evoked pressure curves (EPCs) from the external
anal sphincter muscle (EAS). MEPs and EPCs were simultaneously
recorded following transcranial magnetic stimulation of the motor
cortex. Voluntary contractions were also studied. Contraction times
of the EAS were significantly longer in voluntary contractions (mean:
237msec) than in EPCs (mean: 90msec). Depending on either mode of
contraction, contraction times varied only slightly despite a wide
range of contraction strengths. It is shown, that the contractile
behavior of the EAS is a function of slow and fast twitch muscle
fiber distribution and that the principle of isochronism governs
motor performance not only of limb muscles but also of the EAS. There
exists a unique optimal working range of each muscle in order to meet
its individual function. Disturbance of this principle results in a
less efficient contraction with either inappropriate basic tone or
disturbed reflex activation in the EAS. Both are possible causes of
incontinence.
Received 8 November 1994; accepted in final form 20 March 1995.
APS Manuscript Number G446-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.