Am. J. Respir. Crit. Care Med., Vol 155, No. 5, 05 1997, 1575-1582.
Relaxation is impaired in the diaphragm muscle of the cardiomyopathic Syrian hamster
C Coirault, D Chemla, JC Pourny, F Lambert, B Riou and Y Lecarpentier
INSERM 451-Laboratoire d'Optique Appliquee-ENSTA-Ecole Polytechnique, Departement d'Anethesie-Reanimation, Universite Paris VI, France.
Relaxation was examined in diaphragm muscle strips of cardiomyopathic
Syrian hamsters and control hamsters. Isotonic lengthening velocity and
isometric tension decay were analyzed over the load continuum in response
to twitch. For each load level (P), we measured the maximum extent of
shortening (deltaL), the peak lengthening velocity (VL), and the peak rate
of tension decline (-dP/dtmax). The kinetics of sarcomere length (SL) were
simultaneously measured by laser diffraction. In an attempt to account for
the influence of shortening and/or load on relaxation, we calculated the
slopes of the VL - deltaL and -dP/dtmax - P relationships. In both groups,
there was a direct relationship between (1) VL and deltaL and (2) -dP/dtmax
and P. In myopathic hamsters, we observed a decrease in the slope of the VL
- deltaL relationship (p < 0.05), a decrease in VL at any common value
of both muscle and sarcomere extent of shortening, and an increase in the
duration of overall lengthening. Isometric tension decay was significantly
prolonged in myopathic muscle strips, while the -dP/dtmax - P relationship
was not significantly different than in controls. At low-to-medium loads,
SLs at the onset of tension decline were greater in myopathy. These data
indicate that relaxation of the diaphragm was both slowed and prolonged in
myopathic Syrian hamsters.
