Influence of global inspiratory muscle fatigue on breathing during
exercise.
Paweliwiski, Sheng Yan, Alain P. Gauthier, and Peter T. Macklem.
Meakins-Christie Laboratories, McGill University Clinics, Royal
Victoria Hospital and the Montreal Chest Hospital, Montreal, Quebec,
Canada
APStracts 2:0516A, 1995.
We evaluated the effect of global inspiratory muscle fatigue (GF) on
respiratory muscle control during exercise at 30%, 60% and 90% of
maximum power output in normal subjects. Fatigue was induced by
breathing against high inspiratory resistance until exhaustion.
Esophageal and gastric pressures, anteroposterior displacement of rib
cage and abdomen, breathing pattern and perceived breathlessness were
measured. Induction of GF had no effect on ventilatory parameters
during mild and moderate exercise. It altered however ventilatory
response to heavy exercise by increasing breathing frequency and
minute ventilation with minor changes in tidal volume. This was
accompanied by an increase in perceived breathlessness. GF
significantly increased both tonic and phasic activity of abdominal
muscles that allowed: the diaphragm to maintain its function while
developing less pressure; the same tidal volume with lesser
shortening of the rib cage inspiratory muscles; relaxation of the
abdominal muscles to contribute to lung inflation. The increased work
performed by the abdominal muscles may however lead to reduction in
their strength. GF may impair exercise performance in some healthy
subjects, that is probably not related to excessive breathlessness or
other ventilatory factors. We conclude that respiratory system is
remarkably adaptable in maintaining ventilation during exercise even
with impaired inspiratory muscle contractility.
Received 5 October 1994; accepted in final form 2 November 1995.
APS Manuscript Number A1034-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95