Am. J. Respir. Crit. Care Med.,
Volume 163, Number 1, January 2001, 49-54
Response of the Canine Internal Intercostal Muscles
to Chest Wall Vibration
DIMITRI
LEDUC,
ERIC
BRUNKO,
and
ANDRÉ
DE TROYER
Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine, and Chest Service, Erasme University Hospital, Brussels; Intensive Care
Unit, Saint-Pierre University Hospital, Brussels; and Brain Research Unit, Brussels School of Medicine, Brussels, Belgium
Although high-frequency mechanical vibration of the rib cage reduces dyspnea, its effects on the respiratory muscles are largely unknown. We have previously shown that in anesthetized dogs,
vibrating the rib cage during inspiration elicits a marked increase
in the inspiratory electromyographic (EMG) activity recorded from
the external intercostal muscles but does not affect tidal volume (VT). In the present studies, we have tested the hypothesis that the maintenance of VT results from the concomitant contraction of the internal interosseous (expiratory) intercostals. When the rib
cage was vibrated (40 Hz) during hyperventilation-induced apnea,
a prominent activity was recorded from the external intercostals but no activity was recorded from the internal intercostals, including when the muscles were lengthened by passive inflation. The
internal intercostals remained also silent when vibration was applied during spontaneous inspiration, and the phasic expiratory
EMG activity recorded from them was unaltered when vibration
was applied during expiration. Thus, the internal interosseous intercostals in dogs are much less sensitive to vibration than the external intercostals, and they do not interfere with the action of
these latter during rib cage vibration. This lack of sensitivity might
be the result of a reflex inhibition of the muscle spindle afferents
by afferents from external intercostal muscle spindles.
