EFFECT OF AORTIC IMPEDANCE ON PRELOAD-AFTERLOAD MISMATCH IN CANINE HEARTS IN-SITU

The aim was to examine the influence of the independent increase of ao rtic wall characteristics from vascular resistance on global left vent ricular (LV) function in intact hearts. In 11 anesthetized dogs, aorti c stiffness was increased by a constriction of the thoracic aorta usin g a stiff tube, and then, in nine dogs, total systemic resistance (TSR ) was increased by an infusion of angiotensin II. During the above pro cedures, aortic input impedance and LV dimension were measured. Aortic input impedance spectra revealed the steady increase in the moduli at high frequencies by aortic constriction, indicating the increase in a ortic stiffness. At the stage of increased aortic characteristic imped ance (Zc) (134 % of control) without a change in TSR, both LV end-dias tolic diameter (LVEDD, 99 %, p < 0.01) and stroke volume (SV, 95 %, p < 0.01) decreased significantly without a change in LV end-systolic di ameter (LVESD). During the increase in TSR produced by angiotensin II (128 % of control) without a change in Zc, LVEDD tended to increase an d LVESD significantly increased (103 %, p < 0.01), associated with a d ecrease in SV (94 %, p < 0.01). LV systolic mean wall stress was incre ased by angiotensin II (118 %, p < 0.01), whereas it was unchanged by aortic constriction. In conclusion, the isolated increase in aortic st iffness without a change in TSR was associated with a reduction in LV preload and SV.