Journal of Applied Physiology, Vol 55, Issue 2 307-315, Copyright © 1983 by American Physiological Society
Expiratory threshold load under extracorporeal circulation: effects of vagal afferents
Y. Jammes, P. T. Bye, R. L. Pardy, C. Katsardis, S. Esau and C. Roussos
Nine anesthetized dogs breathed against an expiratory threshold load (ETL)
applied by switching the expiratory circuit into a column of H2O to a depth
of 20-30 cm. Arterial blood gas tensions were maintained in the normal
range by placing the dogs under arteriovenous bypass to avoid any
uncontrolled chemostimulation. There was an increase in integrated
electromyogram activity of the diaphragm with the ETL. This was rarely
observed after cold block of the vagus nerves which also reduced the evoked
expiratory activity. The ventilatory response to hypercapnia was greatly
depressed under loaded breathing whether vagal afferents were intact or
blocked by cold. Both inspiratory drive and ventilatory timing were
affected, suggesting that the central integration of chemosensitive
afferents was altered. Proof of supraspinal projections of proprioceptive
inputs from abdominal muscles was provided by the demonstration of changes
in ventilatory timing during selective activation of muscle spindles in
abdominal muscles by high-frequency mechanical vibration applied to the
linea alba. Thus these observations suggest that during ETL breathing, a
possible interaction exists between chemoreflex drive and proprioceptive
afferents.
