On the mechanism of the mediolateral gradient of parasternal
activation.
Troyer, Andr[acute]e De, Alexandre Legrand, Ghislaine Gayan-Ramirez,
Matteo Cappello, and Marc Decramer.
Laboratory of Cardiorespiratory Physiology, Brussels School of
Medicine, and Chest Service, Erasme University Hospital, 1070
Brussels; and Respiratory Muscle Research Unit and Respiratory
Division, University Hospital, Gasthuisberg, 3000 Leuven, Belgium
APStracts 3:0007A, 1996.
Recent studies have shown that in spontaneously breathing dogs, the
parasternal intercostals are activated according to a mediolateral
gradient. To assess the mechanism of this regionalization of
activity, we have assessed the pattern of activation of these muscles
after section of the dorsal roots, and we have examined the
topographic distribution of the muscle fiber-types from the sternum
to the chondrocostal junctions. The pattern of parasternal activity
after dorsal rhizotomy was similar in all respects to that previously
observed in intact animals. Thus, activity in the medial parasternal
bundles at the onset of inspiration frequently preceded activity in
the middle bundles, and no activity was recorded from the lateral
bundles. The amount of medial activity, when expressed as a
percentage of the activity recorded during supramaximal, tetanic
stimulation of the internal intercostal nerve (maximal activity), was
also consistently greater than the amount of middle activity (52.6
+/- 4.6 vs. 23.1 +/- 2.6% max; P< 0.001). Furthermore, the
medial, middle, and lateral parasternal bundles had a higher
proportion of S0 fibers than FOG fibers; no topographic difference in
fiber-type distribution was observed. We conclude, therefore, that
the mediolateral gradient of parasternal activity is probably due to
the unequal distribution of central inputs throughout the pool of
[alpha]-motoneurones.
Received 21 February 1995; accepted in final form 13 December
1995.
APS Manuscript Number A195-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96