EFFECTS OF PRELOAD ON REGIONAL NONISCHEMIC END-SYSTOLIC PERFORMANCE

Background Nonischemic segmental performance, assessed by end-systolic measures of shortening and thickening, decreases during ischemia, The se changes in performance are likely to be dependent on the size, and, possibly, the site of the ischemic zone. This study was designed to e xamine the effect of preload, independently from ischemic zone size, o n nonischemic end-systolic performance. Methods Twelve beagles were in strumented with sonomicrometers and micromanometer pressure gauges. En d-systolic pressure length and thickness relationship data were obtain ed during vena caval balloon inflation, Control data were obtained bot h in left anterior descending and in left circumflex regions at left v entricular end-diastolic pressures of 5, 10 and 15 mmHg, The left circ umflex artery was occluded for 90 s and nonischemic end-systolic press ure length and thickness data were obtained at each diastolic pressure , A 20 min recovery period was allowed between coronary occlusions, Re sults The isovolumic bulge in the ischemic area was more pronounced at an end-diastolic pressure of 5 mmHg than it was at an end-diastolic p ressure of 15 mmHg, The slope of the nonischemic end-systolic pressure length and thickness relationships decreased at an end-diastolic pres sure of 5 mmHg, whereas at 10 and 15 mmHg the slope of these relations hips did not change significantly. The shift in the nonischemic end-sy stolic pressure-length relationship to the right was more pronounced a t a low end-diastolic pressure (5 mmHg) than it was at a high end-dias tolic pressure (15 mmHg). Similarly, the extent of the shift in the en d-systolic pressure-thickness relationship to the left was more marked at a low end-diastolic pressure than it was at the higher end-diastol ic pressure, Conclusion Regional ischemia decreases the end-systolic p erformance of the nonischemic region. The extent of the shift and the degree to which the slopes of the nonischemic end-systolic relations d ecrease are influenced by loading conditions.