Journal of Applied Physiology, Vol 66, Issue 3 1455-1461, Copyright © 1989 by American Physiological Society
Effect of intestinal afferent stimulation on pattern of respiratory muscle activation
S. B. Gottfried and A. F. DiMarco
Department of Medicine, Montreal General Hospital, Meakins-Christie Laboratories, McGill University, Quebec, Canada.
The purpose of the present study was to examine the reflex effects of
mechanical stimulation of intestinal visceral afferents on the pattern of
respiratory muscle activation. In 14 dogs anesthetized with pentobarbital
sodium, electromyographic activity of the costal and crural diaphragm,
parasternal intercostal, and upper airway respiratory muscles was measured
during distension of the small intestine. Rib cage and abdominal motion and
tidal volume were also recorded. Distension produced an immediate apnea
(11.16 +/- 0.80 s). During the first postapneic breath, costal (43 +/- 7%
control) and crural (64 +/- 6% control) activity were reduced (P less than
0.001). In contrast, intercostal (137 +/- 11%) and upper airway muscle
activity, including alae nasi (157 +/- 16%), genioglossus (170 +/- 15%),
and posterior cricoarytenoid muscles (142 +/- 7%) all increased (P less
than 0.005). There was greater outward rib cage motion although the abdomen
moved paradoxically inward during inspiration, resulting in a reduction in
tidal volume (82 +/- 6% control) (P less than 0.005). Postvagotomy
distension produced a similar apnea and subsequent reduction in costal and
crural activity. However, enhancement of intercostal and upper airway
muscle activation was abolished and there was a greater fall in tidal
volume (65 +/- 14%). In conclusion, mechanical stimulation of intestinal
afferents affects the various inspiratory muscles differently; nonvagal
afferents produce an initial apnea and subsequent depression of diaphragm
activity whereas vagal pathways mediate selective enhancement of
intercostal and upper airway muscle activation.
