Journal of Applied Physiology, Vol 68, Issue 1 35-43, Copyright © 1990 by American Physiological Society
Respiratory changes in diaphragmatic intramuscular pressure
M. Decramer, T. X. Jiang and M. B. Reid
Respiratory Division, Academic Hospital, Pellenberg, Belgium.
We attempted to measure diaphragmatic tension by measuring changes in
diaphragmatic intramuscular pressure (Pim) in the costal and crural parts
of the diaphragm in 10 supine anesthetized dogs with Gaeltec 12 CT
minitransducers. During phrenic nerve stimulation or direct stimulation of
the costal and crural parts of the diaphragm in an animal with the chest
and abdomen open, Pim invariably increased and a linear relationship
between Pim and the force exerted on the central tendon was found (r
greater than or equal to 0.93). During quiet inspiration Pim in general
decreased in the costal part (-3.9 +/- 3.3 cmH2O), whereas it either
increased or slightly decreased in the crural part (+3.3 +/- 9.4 cmH2O, P
less than 0.05). Similar differences were obtained during loaded and
occluded inspiration. After bilateral phrenicotomy Pim invariably decreased
during inspiration in both parts (costal -4.3 +/- 6.4 cmH2O, crural -3.1
+/- 0.6 cmH2O). Contrary to the expected changes in tension in the muscle,
but in conformity with the pressure applied to the muscle, Pim invariably
increased during passive inflation from functional residual capacity to
total lung capacity (costal +30 +/- 23 cmH2O, crural +18 +/- 18 cmH2O).
Similarly, during passive deflation from functional residual capacity to
residual volume, Pim invariably decreased (costal -12 +/- 19 cmH2O, crural
-12 +/- 14 cmH2O). In two experiments similar observations were made with
saline-filled catheters. We conclude that although Pim increases during
contraction as in other muscles, Pim during respiratory maneuvers is
primarily determined by the pleural and abdominal pressures applied to the
muscle rather than by the tension developed by it.
