Journal of Applied Physiology, Vol 66, Issue 1 384-391, Copyright © 1989 by American Physiological Society

ARTICLES

Differential responses of expiratory muscles to chemical stimuli in awake dogs

C. A. Smith, D. M. Ainsworth, K. S. Henderson and J. A. Dempsey
John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin School of Medicine, Madison 53705.

We assessed respiratory muscle response patterns to chemoreceptor stimuli (hypercapnia, hypoxia, normocapnic hypoxia, almitrine, and almitrine + CO2) in six awake dogs. Mean electromyogram (EMG) activities were measured in the crural (CR) diaphragm, triangularis sterni (TS), and transversus abdominis (TA). Hypercapnia and normocapnic hypoxia caused mild to marked hyperpnea [2-5 times control inspiratory flow (VI)] and increased activity in CR diaphragm, TS, and TA. When hypocapnia was permitted to develop during hypoxia and almitrine-induced moderate hyperpnea, CR diaphragm activity increased, whereas TS and TA activities usually did not change or were reduced below control. Over time in hypercapnia, CR diaphragm, TS, and TA were augmented and maintained at these levels over many minutes; with hypoxic hyperventilation CR diaphragm, TS, and TA were first augmented but then CR diaphragm remained augmented while TS and, less consistently, TA were inhibited over time. Marked hyperpnea (4-5 times control) due to carotid body stimulation increased TA and TS EMG activity despite an accompanying hypocapnia. We conclude that in the intact awake dog 1) carotid body stimulation augments the activity of both inspiratory and expiratory muscles; 2) hypocapnia overrides the augmenting effect of carotid body stimulation on expiratory muscles during moderate hyperpnea, usually resulting in either no change or inhibition; 3) at higher levels of hyperpnea both chemoreceptor stimulation and stimulatory effects secondary to a high ventilatory output favor expiratory muscle activation; these effects override any inhibitory effects of a coincident hypocapnia; and 4) expiratory muscles of the rib cage/abdomen may be augmented/inhibited independently of one another.

This article has been cited by other articles:

				J. L. Smith, J. E. Butler, P. G. Martin, R. A. McBain, and J. L. Taylor Increased ventilation does not impair maximal voluntary contractions of the elbow flexors J Appl Physiol, June 1, 2008; 104(6): 1674 - 1682. [Abstract] [Full Text] [PDF]

				A. De Troyer, P. A. Kirkwood, and T. A. Wilson Respiratory Action of the Intercostal Muscles Physiol Rev, April 1, 2005; 85(2): 717 - 756. [Abstract] [Full Text] [PDF]

				D. C. Poole, W. L. Sexton, B. J. Behnke, C. S. Ferguson, K. S. Hageman, and T. I. Musch Respiratory muscle blood flows during physiological and chemical hyperpnea in the rat J Appl Physiol, January 1, 2000; 88(1): 186 - 194. [Abstract] [Full Text] [PDF]