Variations of Blood Pooling in Coronary Vascular Beds

Abstract

The myocardium is highly vascular, consisting of 10% — 15% of blood at diastolic volume. Thereby coronary blood volume (CBV) affects both coronary hemodynamics and myocardial properties. The aims of this study were to assess: (a) variations of CBV in beating hearts with heart rate (HR) changes and (b) the effects of coronary venous pressure (VP) on diastolic myocardial properties. (a) To assess CBV, we measured myocardial volume in LV-isovolumically beating and vasodilated dog hearts mounted in a newly-developed pressure type plethysmography system. HR varied from 60 to 180 bpm when perfusion pressure (PP) was maintained constant at approximately either 70 or 40 mmHg. Mean CBV decreased linearly with reduced RR intervals at both PP, the decrease being significantly larger at a PP of 70, i.e., CBV = 3.5 × RR — 1.8 (PP = 70) vs CBV = 2.1 × RR — 1.0 (PP = 40), P < 0.005. These results suggest that HR and PP play important interdependent roles in determining CBV. (b) To assess the effect of CBV on diastolic myocardial distensibility, we studied excised, LV isovolumic dog hearts in which VP and right ventricular pressure (RVP) were manipulated separately. LV wall volume was determined by subepicardial segment length at end-diastole. Both VP and RVP were increased, from 0 to 30 mmHg, over a range of LV volumes. Left ventricular end-diastolic pressure (LVEDP) (mmHg) data are shown in the Table.