Journal of Applied Physiology, Vol 72, Issue 1 288-292, Copyright © 1992 by American Physiological Society
Effect of abdominal compression on diaphragmatic tendon organ activity
R. Revelette, S. Reynolds, D. Brown and R. Taylor
Department of Physiology and Biophysics, University of Kentucky, Lexington 40536-0084.
Previous studies suggest that afferents in the diaphragm participate in the
reflex reduction in phrenic nerve efferent activation when the length of
the diaphragm is increased by abdominal compression. The present study
determined the response of tendon organ afferents in the diaphragm to
increases in abdominal pressure. Five cats were anesthetized with
thiopental sodium (60 mg/kg ip to induce, supplemented intravenously).
Extracellular recordings from nine individual tendon organ afferents were
made from right cervical dorsal root ganglia 5 and 6. Right crural
electromyographic activity was recorded. The right extrathoracic phrenic
nerve was isolated and stimulated to identify tendon organs on the basis of
conduction velocity and response to twitch. The response to ramp-and-hold
stretch of the diaphragm was used as an additional test to differentiate
tendon organs from muscle spindles. The mean level of activity of the
tendon organs during the 1st s of the inspiratory phase was 47 +/- 10 (SD)
Hz. Abdominal compression was associated with a significant increase in the
activity of these afferents to 61 +/- 11 Hz. Results indicate that
increases in the activity of diaphragmatic tendon organs are associated
with moderate increases in abdominal pressure and are likely the result of
elevations in the active tension developed by the diaphragm. Combined with
results from previous studies, it is possible that diaphragmatic tendon
organs may play a role in the attenuation of respiratory muscle activation
when abdominal pressure is increased.
