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Left coronary pressure-flow relations of the beating and arrested rabbit heart at different ventricular volumes
P Sipkema1, J J Takkenberg, P E Zeeuwe
1Laboratory for Physiology, Vrije Universiteit (ICaR-VU), Amsterdam, The Netherlands. p.sipkema.physiol@med.vu.nl
Objective:
To study the effect of cardiac contraction on left coronary artery pressure-flow relations at different vascular volumes and to compare these relations in the beating heart with those in the heart arrested in systole and diastole.
Methods:
Maximally vasodilated, Tyrode perfused, rabbit hearts (n = 6) with an intra-ventricular balloon were used. The left coronary artery was separately perfused via a cannula in the left main coronary artery. The slopes and the intercepts of left coronary pressure-flow relations were determined in the beating and arrested heart at different chamber volumes. A 3-factor design with repeated measures was used to compare the effect of three factors: phase of contraction (systole and diastole), chamber volume (V0 and V1, left ventricular end-diastolic pressure 1.4 and 20 mm Hg, respectively) and the type of contraction (beating and arrested; a measure of capacitive effects).
Results:
The phase of contraction has a significant effect on the intercepts (> 40 mmHg, p = 0.00032) but not on the slopes of the pressure-flow relations. Chamber volume had a small effect on the intercepts (< 5 mm Hg, p = 0.037), but not on the slopes of the pressure-flow relations. The type of contraction has a significant effect on the slopes (approximately 10%, p = 0.00021) but not on the intercepts of the pressure-flow relations.
Conclusions:
In the isolated Tyrode perfused rabbit heart left coronary pressure-flow relations are mainly determined by contraction, while left ventricular chamber volume and capacitive effects contribute little.