Journal of Applied Physiology, Vol 64, Issue 2 846-853, Copyright © 1988 by American Physiological Society
Rib cage and abdominal expiratory muscle responses to CO2 and esophageal distension
E. van Lunteren, M. A. Haxhiu, N. S. Cherniack and J. S. Arnold
Department of Medicine, University Hospitals of Cleveland, Ohio.
The present study compared the responses of rib cage and abdominal
expiratory muscles to chemical and mechanical stimuli. In
pentobarbital-anesthetized spontaneously breathing dogs, electromyograms
(EMG) were recorded from the triangularis sterni (TS) and transverse
abdominis (TA) muscles using bipolar intramuscular wire electrodes. During
resting oxygen breathing, both muscles were electrically active during
expiration. Progressive hyperoxic hypercapnia significantly augmented the
expiratory activity of both the TA and the TS. However, the mean percent
increases in electrical activity in response to CO2 were substantially
greater for the TA than for the TS at all PCO2 levels greater than 50 Torr
(P less than 0.01). Occlusion of the airway at end inspiration
significantly delayed the onset of TS EMG (from 0.35 +/- 0.07 to 3.35 +/-
0.67 sec; P less than 0.002) and decreased TS EMG rate of rise (P less than
0.002), but did not significantly alter these parameters for the TA.
Esophageal distension increased TS EMG in all dogs (by mean of 220 +/- 64%;
P less than 0.01), but in contrast decreased TA EMG in all dogs (by a mean
of 63 +/- 12%; P less than 0.001). The response to esophageal distention
occurred in a graded manner and appeared to be mediated predominantly via
vagal afferents. We concluded that expiratory muscles of the rib cage and
abdomen manifest substantial differences in their electrical responses to
chemoreceptor, pulmonary stretch receptor, and esophageal mechanoreceptor
stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
