Left ventricular performance at high end-diastolic pressures in isolated, perfused dog hearts

In the isolated, blood-perfused heart of the dog, left ventricular developed pressure and developed mean wall stress were observed while the ventricle contracted at a constant, nearly isovolumic afterload and while end-diastolic pressure was raised to levels exceeding 100 mm Hg. Coronary perfusion pressure was maintained at the level of the peak systolic pressure. Dilatation of the mitral ring and consequent mitral regurgitation were avoided by left atrial plication. Normalized graphs of percent of peak developed pressure against end-diastolic pressure showed that developed pressure rose abruptly with diastolic pressure, peaked at a diastolic pressure of approximately 30 mm Hg, and declined 14.7% (±0.9 SE) at an end-diastolic pressure of 100 mm Hg. Likewise, developed mean wall stress rose abruptly with diastolic pressure, peaked at a higher diastolic pressure of approximately 50 mm Hg, and declined only 7.5% (±0.8 SE) from this peak at an end-diastolic pressure of 100 mm Hg. Similar findings were observed in hearts acutely depressed with propranolol. Electron micrographs showed sarcomere length to average 2.275µ and 2.300µ in ventricles fixed in diastole while subjected to pressures of 61 and 100 mm Hg, respectively, after potassium arrest, confirming the findings illustrated by the normalized graphs. These observations imply that in the isolated heart of the dog there is no loss of ventricular performance attributable to a descending limb of the Frank-Starling mechanism until the end-diastolic pressure exceeds 60 mm Hg and that this loss is minimal at diastolic pressures as high as 100 mm Hg.

Distribution of ions and water between tissue compartments in the perfused left ventricle of the rat heart

Left ventricles from rat hearts were perfused through the coronary blood vessels for periods up to 90 minutes with solution containing radioactively labeled sulfate, sucrose, urea, glycerol, or chloride. Urea and glycerol equilibrate with all of tissue water. By contrast, 35 SO 4 and sucrose- 14 C equilibrate very rapidly with 40% of total water and slowly with an additional 20%; they are excluded from 40% of the tissue water. The two "cellular" compartments (C 2 , which equilibrates slowly with SO 4 and sucrose, and C 3 , from which SO 4 and sucrose are excluded) both lose water when hearts are perfused with a solution made hypertonic with NaCl. Chemical analyses for K, Na, and Cl, and measurements of the rate of equilibration of 36 C1 show that C 2 has low contents of Cl and Na. Experiments in which extracellular NaCl was replaced osmole for osmole by KCl according to the method of Boyle and Conway suggest that the boundaries of C 2 and C 3 may have different ionic permeabilities. These observations indicate that the division of mammalian heart muscle into tissue compartments is more complex than conventionally assumed, a conclusion reached by Bozler for frog heart muscle. They are inconsistent with the usual assumption that cardiac cellular water is homogeneous.