title: Left ventricular systolic resistance in rats with hypertension and hypertrophy.
abstract: Traditional indexes of ventricular performance often fail to identify differences between the normal and hypertrophied ventricle. This may not be the case for load-independent mechanical properties, elastance, and resistance. Accordingly, we derived these properties of the intact left ventricle (LV) in 25-wk-old male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto controls (WKY) using in-situ and isolated hearts. We found that 1) pump performance was similar in SHR and WKY, both at base line and after dextran; 2) the peak systolic elastance (Emax) was higher and theoretical maximum flow (Qmax, inverse of ventricular resistance) was lower in SHR; (3) slopes of peak isovolumetric pressure-volume and stress-strain relations were significantly higher in SHR; and 4) although end-diastolic pressure-volume relation for SHR was shifted to the right, there was no difference in end-diastolic stress-strain relations. Thus elastance in hypertrophied LV is augmented due to both an increase in muscle mass and the force-generating capacity of the myocardium. Furthermore, we propose that the decrease in Qmax seen in SHR reflects a change in certain velocity-dependent properties of the myocardium, whereas the preservation of pump performance is a result of the opposing effects of increased Emax and decreased Qmax. These observations underscore the importance of quantifying systolic resistance, together with elastance, for a better assessment of the LV as a mechanical pump.
authors.affiliation: Cardiovascular Institute, Michael Reese Hospital and Medical Center, University of Chicago Pritzker School of Medicine, Illinois 60616.
authors.forename: S G
authors.initials: SG
authors.lastname: Shroff
authors.forename: W
authors.initials: W
authors.lastname: Motz
mesh_terms: D000818:Animals; D001794:Blood Pressure; D006332:Cardiomegaly / Q000503:physiopathology*; D004548:Elasticity; D006321:Heart / Q000503:physiopathology*; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008433:Mathematics; D008955:Models, Cardiovascular; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012016:Reference Values; D013599:Systole; D014655:Vascular Resistance; D016276:Ventricular Function