AJP - Heart and Circulatory Physiology, Vol 260, Issue 3 702-H712, Copyright © 1991 by American Physiological Society
Diastolic stiffness impairs left ventricular function during hypovolemic shock in pigs
K. R. Walley and D. J. Cooper
Pulmonary Research Laboratory, St. Paul's Hospital, University of British Columbia, Vancouver, Canada.
To determine the causes of impaired left ventricular function during
hypovolemic shock we measured diastolic and end-systolic pressure-volume
relationships and hemodynamics. Left ventricular pressure (Millar catheter)
and volume (3 ultrasonic crystal pairs) were measured in six open-chest,
chloralose-morphine anesthetized, juvenile pigs. After baseline
measurements, the pigs were bled and maintained at a mean aortic pressure
of 50 cmH2O for 7 +/- 1 h. After resuscitation with all shed blood, left
ventricular function was markedly impaired as indicated by increased
end-diastolic pressure (20.3 vs. 8.7 cmH2O at baseline, P less than 0.05),
decreased aortic pressure (36% of baseline, P less than 0.01), and
decreased stroke volume (50% of baseline, P less than 0.01). Systolic
contractility was increased (P less than 0.05), but diastolic compliance
was greatly reduced due to decreased diastolic maximum (52% of baseline, P
less than 0.01) and equilibrium volumes (57% of baseline, P less than
0.01). We conclude that impaired left ventricular function during
hypovolemic shock is due entirely to increased diastolic stiffness. These
results can theoretically be accounted for by a 20% reduction in myocardial
muscle length with no change in muscle stress-strain characteristics. This
may be the physiological expression of morphologically observed myocardial
"zonal lesions" of hypovolemic shock.
