Regional end-systolic pressure-length relationships using a volume-loading technique in the intact pig heart.
The purpose of this study was to characterize left ventricular systolic elastances as derived from pressure-segment length and pressure-diameter relationships, and to compare the resulting regional and global elastances to known changes in inotropy. Left ventricular pressure-segment length and pressure-diameter were varied in a series of consecutive beats by means of a volume-loading technique, and both regional and global relationships at 20-msec intervals throughout systole were found to be nonlinear and to exhibit hysteresis. In eight animals, regional hysteresis was present after vagotomy, propranolol (1.0 mg/kg), and atropine (0.1 mg/kg), and was present no matter whether hearts were loaded by volume (45-60 ml/sec) or by pressure (partial aortic occlusion) over a similar range of left ventricular systolic pressures. Elastance was linearly approximated by the slope of the major axis of the hysteresis loops. In each instance, elastance increased to a maximum and then decreased, thus defining end-systole. In seven animals, maximum elastance-length and -diameter were compared before and after treatments with dobutamine (5-13 micrograms/kg per min) and propranolol (6-51 micrograms/kg per min), or after induction of global ischemia. Dobutamine increased maximum elastance-diameter by 37% (P less than 0.01) and maximum elastance-length by 159% (P less than 0.05). Propranolol decreased maximum elastance-diameter by 27% (P less than 0.05) and maximum elastance-length by 6% (P = NS). Global ischemia (50% reduction in coronary flow) did not significantly change either maximum elastance-diameter or -length. However, with ischemia, the diameter intercept of maximum elastance-diameter increased by 24% (P less than 0.025), and the time to maximum elastance-length decreased by 33% (P less than 0.01). Comparing all interventions, the percent changes in maximum elastance-length and -diameter related directly but with a low correlation coefficient (r = 0.49). These differences in regional and global elastance suggest a complex relationship between regional and global myocardial mechanics, and may not necessarily reflect specific changes in contractility.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002306:Cardiac Volume; D003327:Coronary Disease / Q000503:physiopathology; D003331:Coronary Vessels / Q000502:physiology / Q000503:physiopathology; D004280:Dobutamine / Q000494:pharmacology; D004548:Elasticity; D005260:Female; D006321:Heart / Q000502:physiology* / Q000503:physiopathology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D011312:Pressure; D011433:Propranolol / Q000494:pharmacology; D013552:Swine; D013599:Systole
D004280:Dobutamine; D011433:Propranolol