Effect of chest wall vibration on the canine diaphragm during breathing.

High-frequency mechanical vibration of the ribcage reduces dyspnoea in patients with chronic obstructive pulmonary disease, and the suggestion has been made that this effect might be related to a decrease in central respiratory drive resulting from an increase in afferent inputs from intercostal muscles. In the present studies, the effects of ribcage vibration on central respiratory drive have been assessed without the confounding influence of conscious reactions. The electromyographic (EMG) activity of the diaphragm and the changes in pleural (Ppl) and abdominal (Pab) pressure were measured in six anaesthetized, spontaneously-breathing dogs while the rostral, the middle, or the caudal portion of the ribcage was vibrated at intervals during inspiration. The EMG activity of the external and parasternal intercostals was also measured. Ribcage vibration consistently elicited a marked increase in the inspiratory EMG activity recorded from the external intercostals, thus indicating that the procedure did activate intercostal muscle spindles. However, no alteration in diaphragmatic or parasternal intercostal EMG activity was seen in any animal. Transdiaphragmatic pressure and the relationship between deltaPab and deltaPpl during inspiration were also unaltered. The authors conclude that ribcage vibration and, with it, stimulation of external intercostal muscle spindles has no significant influence on phrenic motoneurones or on medullary inspiratory neurones. It is unlikely, therefore, that the beneficial effect of the procedure on dyspnoea results from a specific reduction in central respiratory drive.