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, mm Hg) are associated with increases in left ventricular (LV) function which persist even after diastolic volume has returned to its initial value (Anrep effect). Likewise, increases in coronary arterial pressure (CAP, mm Hg) are associated with improved LV function (gardenhouse 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 AoP and CAP increases on function (peak systolic pressure: LVPmax, mm Hg; dP/dtmax, mm Hg/s; end-diastolic pressure: LVPed, mm Hg) and end-diastolic geometry (inner diameter: IDed, mm; wall thickness: WTed, mm; sonomicrometry). CAP-induced increases in coronary flow were prevented by admixing dextran to the perfusate. The experiments were performed on isolated, saline-perfused, working rabbit hearts. Increasing CAP from 60 to 80 mm Hg (n = 11) resulted in improved function: LVPmax 89 +/- 3 vs. 94 +/- 3, dP/dtmax 1160 +/- 50 vs. 1250 +/- 50, LVPed 17 +/- 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 LVPmax, dP/dtmax and LVPed increased (90 +/- 4 vs. 97 +/- 3, 1170 +/- 70 vs. 1270 +/- 90 and 18 +/- 1 vs. 19 +/- 1). IDed increased from 9.76 +/- 0.39 to 9.99 +/- 0.37 and WTed decreased from 6.08 +/- 0.22 to 5.86 +/- 0.25. After additionally increasing CAP to 80, function further improved (LVPmax: 101 +/- 3, dP/dtmax: 1310 +/- 80) while LVPed 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 function via the gardenhose effect and likely do not depend on simultaneous increases in coronary flow or oxygen supply. On the other hand, increases in AoP alone improve systolic function via the Frank-Starling mechanism. Increases in both pressures together amplify this effect. Increases in CAP and in AoP have opposing effects on IDed and WTed. In conclusion, the homeometric Anrep effect--at least in part--can be viewed as synergistic action of the Frank-Starling mechanism and the gardenhose effect for this experimental model.