Journal of Applied Physiology, Vol 68, Issue 3 868-875, Copyright © 1990 by American Physiological Society
Respiratory changes in parasternal intercostal intramuscular pressure
P. Leenaerts and M. Decramer
Respiratory Division, Katholieke Universiteit Leuven, Belgium.
In an attempt to obtain insight in the forces developed by the parasternal
intercostal muscles during breathing, changes in parasternal intramuscular
pressure (PIP) were measured in 14 supine anesthetized dogs using a
microtransducer method. In six animals, during bilateral parasternal
stimulation a linear relationship between contractile force exerted on the
rib and PIP was demonstrated (r greater than 0.95). In eight animals,
during quiet active inspiration, substantial (55 +/- 11.5 cmH2O) PIP was
developed. During inspiratory resistive loading and airway occlusion the
inspiratory rise in PIP increased in proportion to the inspiratory fall in
pleural pressure (r = 0.82). Phrenicotomy and vagotomy resulted in an
increase in the inspiratory rise in PIP of 21% and 99%, respectively.
During passive deflation, when the parasternal intercostals were passively
lengthened, large rises (320 +/- 221 cmH2O) in intramuscular pressure were
observed. During passive inflation intramuscular pressure remained constant
or even decreased slightly (-8 +/- 25 cmH2O) as expected on the basis of
the passive shortening of the muscles. PIP thus invariably increased when
tension increased either actively or passively. From PIP it is clear that
the parasternals exert significant forces on the ribs during respiratory
maneuvers.
