Left ventricular shape-luminal pressure relationship. An open-chest study

Left ventricular dimensions were measured in Cd2+ arrested (presumably diastolic), open-chest rats. Aortic pressure was maintained at 137 cm H2O (100 mm Hg) and left-ventricular (luminal) pressures were established and maintained at their chosen values, each by means of reservoir systems. The selected left-ventricular pressures were chosen to be within or to even broaden the range of conceivable diastolic pressures (-3 to 48 cm H2O). After in situ fixation with 4% formaldehyde and gelatin embedding, the hearts were serially sectioned in the apex base direction to obtain information at 11 levels (10, 20, . . . 90, 100%). Tracings of selected sections were made along the edge of the left ventricular lumen and the pericardial surface. Volumes, surface areas, and mean external and internal radii of the left ventricle were derived. To quantify the circularity of sections a form factor (FF) was introduced (FF = 1 for a circular cross-section and less than one for other shapes). Ventricular lengths, radial dimensions, endocardial and epicardial surface areas, and total and luminal volumes increased with the increasing intraventricular pressures; as expected, the wall simultaneously thinned. Though its appearance was altered by the wall thinning, the curving muscle fascicular pattern was present over the entire pressure range examined. Endocardial surface areas increased more than did the epicardial surface areas. The endocardial FF value increased (more circular) at each section level as the pressure increased. The epicardial FF relationship was apparently constant (0.798 +/- 0.014) for all section levels from 10% through 90%, regardless of luminal pressure. These results, when taken in conjunction with the results of our previous published studies, prompted the following speculation. The wall of the diastolic ventricle is a fluid-filled chamber with intramyocardial pressures that may be higher than ventricular pressures.