TEMPORAL SEQUENCE OF ENDOTOXIN-INDUCED SYSTOLIC AND DIASTOLIC MYOCARDIAL DEPRESSION IN RABBITS

Twelve anesthetized rabbits received endotoxin (175 +/- 38 mug/kg iv, mean +/- SD) to evaluate the temporal sequence of alterations in left ventricular (LV) function. LV volume was calculated from LV minor- and long-axis diameters, and wall thickness was measured with sonomicrome ters. Hypotension, acidosis, and hypoxia were immediately corrected to eliminate these causes of myocardial depression. LV dilation develope d early (1.2 +/- 0.5 h) with a significant (21 +/- 23%) increase in en d-diastolic volume measured at a LV end-diastolic pressure of 5 +/- 6 mmHg. The LV stiffness did not change, and the LV dilation did not pro gressively worsen. Significant systolic depression developed later (2. 8 +/- 1.0 h) with a 32 +/- 22% increase in end-systolic volume measure d at a LV end-systolic pressure of 69 +/- 9 mmHg. The late preterminal phase (4.1 +/- 0.8 h) was characterized by a progressive increase in end-systolic volume (73 +/- 41% above control) and a significant (53 /- 34%) increase in tau, the time constant of LV pressure fall. Diasto lic abnormalities (LV dilation and increased tau) were not attributabl e to depressed contractility or altered hemodynamics. We conclude that endotoxin impairs systolic and diastolic LV function with distinct di fferences in time course. This suggests that contractility, relaxation , and passive LV properties are impaired by different endotoxin-mediat ed pathways and/or have different sensitivities to endotoxin.