Am. J. Respir. Crit. Care Med., Vol 149, No. 1, Jan 1994, 168-173.
The comparative effects of elastase-induced emphysema on costal and crural diaphragm and parasternal intercostal muscle contractility
SG Kelsen, WP Sexauer, IA Mardini and GJ Criner
Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania.
Chronically, hyperinflated human subjects with chronic obstructive
pulmonary disease and animals with experimentally induced emphysema
generate greater than expected levels of transdiaphragmatic pressure at
high lung volume because of adaptive changes in the length-tension
relationship of the costal diaphragm. The ability to lower intrathoracic
pressure during inspiration depends on the mechanical action of all the
inspiratory muscles acting in concert. However, the effect of chronic
hyperinflation on the mechanical action of inspiratory muscles other than
the costal diaphragm remains unknown. This study compares the effect of
chronic hyperinflation in the form of elastase-induced emphysema on the
contractile properties of the three major inspiratory muscles of the
hamster (i.e., the costal and crural diaphragm and parasternal
intercostals). Muscles were studied in vitro 6 months after emphysema was
induced by intratracheal injection of elastase. Saline-injected animals
served as controls. TLC in the elastase-injected hamsters was significantly
greater than in controls (12.5 +/- 0.8 ml versus 9.0 +/- 0.3 ml, p <
0.002). Maximal tetanic tension, time to peak tension, maximal velocity of
shortening, and the force-velocity relationship differed among the three
muscles but for any given muscle were similar in control and emphysematous
animals. In contrast, the fiber length optimal for tension generation (Lo)
not only differed across muscles but was significantly shorter in the
costal diaphragm of emphysematous animals compared with control animals.
However, Lo of the parasternal intercostal and crural diaphragm was similar
in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)
