Dynamics of flow, resistance, and intramural vascular volume in canine coronary circulation

Varying coronary volume will vary vascular resistance and thereby have an e ffect on coronary hemodynamics. Six ventricular septa were isolated from an esthetized dogs, dispersed in a biaxial stretch apparatus at diastolic stre ss, and perfused artificially with an oxygenated perfluorochemical emulsion at maximal. vasodilation. Flow and thickness were measured continuously by an electromagnetic flow probe and sonomicrometer. Pressure was varied sinu soidally around 30, 50, and 70 mmHg with an amplitude of 7.5 mmHg; frequenc ies ranged between 0.015 and 7 Hz. Bode plots of admittance (flow/pressure) and capacitance (scaled thickness/pressure) were constructed. A two-compar tment model was used in which the resistances vary with volume. Realistic v alues of microvascular compliance (similar to 0.3 ml.mmHg(-1).100 g(-1)) we re found. Values 10 times higher were then found when resistances were forc ed to be constant. We concluded that volume dependence of resistances have to,be taken into account when dynamic or static pressure flow relations are studied and conceal the effect of a large intramyocardial compliance on ar terial hemodynamics.