Journal of Applied Physiology, Vol 60, Issue 3 841-845, Copyright © 1986 by American Physiological Society
Differential recruitment of expiratory muscles during opossum development
J. P. Farber
Relationships between time-averaged electromyogram (EMG) discharge in
abdominal (ABD) and lateralintercostal (IC) muscles (interspaces 1-10) were
evaluated when Inactin-anesthetized supine opossums between 20 and 100 days
of age were challenged by positive-pressure breathing (PPB) (3, 6, and 8
cmH2O). Expiratory activity upon initiation of PPB was observed in ABD
muscles after the 30th postnatal day; recruitment of IC muscles requires
further maturation. For example, at a PPB level of 6 cmH2O, animals up to
50-55 days of age recruited IC muscles from the lowest three interspaces on
44% of the occasions where ABD muscles were activated; in older animals the
incidence of IC recruitment increased to 87%. Additionally, the occurrence
of IC relative to ABD recruitment increased with increasing levels of PPB;
IC muscles of highest interspaces (1-3) were activated less often at all
pressures. At the onset of PPB, ABD muscles were usually recruited before
IC muscles; this effect was more prominent in the younger animals. During
the 5th min of PPB, ABD muscles were recruited earlier in expiration than
IC muscles in the majority of animals at all ages. Since IC and ABD motor
groups are activated from similar levels of the spinal cord, the delayed
maturation of IC muscle responses to PPB may reflect developmental
processes involving reflexes from the chest or abdomen, and/or may be a
function of nonrespiratory utilization (i.e., postural) of ABD and IC
muscles.
