EFFECT OF CHANGES IN AORTIC PRESSURE AND IN CORONARY ARTERIAL-PRESSURE ON LEFT-VENTRICULAR GEOMETRY AND FUNCTION ANREP VS GARDENHOSE EFFECT

Sudden increases in aortic pressure (AoP, mmHg) are associated with in creases in left ventricular (LV) function which persist even after dia stolic volume has returned to its initial value (Anrep effect). Likewi se, increases in coronary arterial pressure (CAP, mmHg) are associated with improved LV function (gardenhose effect). In situ, increases in AoP are paralleled by increases in both CAP and coronary blood flow, i .e., oxygen supply. We investigated the individual contributions of Ao P and CAP increases on function (peak systolic pressure: LVP(max), mmH g; dP/dt(max), mmHg/s; end-diastolic pressure: LVP(ed), mmHg) and end- diastolic geometry (inner diameter: IDed, mm; wall thickness: WTed, mm ; sonomicrometry). CAP-induced increases in coronary flow were prevent ed by admiring dextran to the perfusate. The experiments were performe d on isolated, saline-perfused, working rabbit hearts. Increasing CAP from 60 to 80 mmHg (n = 11) resulted in improved function: LVP(max) 89 +/- 3 vs. 94 +/- 3, dP/dt(max) 1160 +/- 50 vs. 1250 +/- 50, LVP(ed) 1 7 +/- 1 vs. 16 +/- 1 (mean +/- SEM). IDed decreased from 9.96 +/- 0.25 to 9.64 +/- 0.33 and WTed increased from 6.02 +/- 0.16 to 6.15 +/- 0. 17. In a second series, AoP was increased from 60 to 80 (n = 9). Both LVP(max), dP/dt(max) and LVP(ed) increased (90 +/- 4 vs. 97 +/- 3, 117 0 +/- 70 vs. 1270 +/- 90 and 18 +/- 1 vs. 19 +/- 1). IDed increased fr om 9.76 +/- 0.39 to 9.99 +/- 0.37 and WTed decreased from 6.08 +/- 0.2 2 to 5.86 +/- 0.25. After additionally increasing CAP to 80, function further improved (LVP(max): 101 +/- 3, dP/dt(max): 1310 +/- 80) while LVP(ed) decreased (18 +/- 1). This time, IDed decreased to 9.71 +/- 0. 36 and WTed increased to 6.03 +/- 0.26. Increases in CAP improve LV fu nction via the gardenhose effect and likely do not depend on simultane ous increases in coronary flow or oxygen supply. On the other hand, in creases in AoP alone improve systolic function via the Frank-Starling mechanism. Increases in both pressures together amplify this effect. I ncreases in CAP and in AoP have opposing effects on IDed and WTed. In conclusion, the homeometric Anrep effect - at least in part - can be v iewed as synergistic action of the Frank-Starling mechanism and the ga rdenhose effect for this experimental model.