Abdominal muscle fatigue following maximum ventilation in man.
Kyroussis, Dimitris, Gary H Mills, Michael I Polkey, Carl-Hugo
Hamnegard, Nicholaos Koulouris, Malcolm Green, and John Moxham.
Royal Brompton and King's College Hospitals, London, U.K.
APStracts 3:0228A, 1996.
Abdominal muscles are the principal muscles of active expiration. To
investigate the possibility of abdominal muscle low frequency fatigue
following maximum ventilation in man we stimulated the nerve roots
supplying the abdominal muscles. We used a magnetic stimulator
(Magstim 200) powering a 90mm circular coil and studied six normal
subjects. To assess the optimum level of stimulation and posture we
stimulated at each intervertebral level between T7 and L1 in the
prone, supine and seated positions. At T10 we used increasing power
outputs to assess the pressure-power relationship. Care was taken to
avoid muscle potentiation. Twitch gastric pressure (Pga) was recorded
using a balloon tipped catheter. Mean (SD) baseline twitch Pga prone
at T10 was 23.5 (5.4) cm H2O . Within occasion mean (SD) twitch Pga
coefficient of variation (COV) was 4.6% (1.1). Twitch Pga was
measured, in the prone position with stimulation over T10 before and
after 2 minutes maximum isocapnic ventilation (MIV). 20 minutes after
MIV mean twitch Pga (SD) fell by 17% (9.1) (p=0.03) and remained low
90 minutes after MIV. We conclude that following maximum ventilation
in man there is reduction of twitch Pga and therefore low frequency
fatigue of abdominal muscles.
Received 18 July 1995; accepted in final form 17 April 1996.
APS Manuscript Number A781-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96