Effects of left ventricular diastolic pressure on the pressure-flow relation of the coronary circulation during physiological vasodilatation

Summary: A study to analyse the effects of left ventricular diastolic pressure on coronary pressure-flow relations during physiological vasodilatation was carried out in 14 anaesthetised dogs. The left circumflex artery was perfused at controlled pressures via an extracorporeal circuit and vasodilatation induced by 15 s occlusion of coronary flow. The relation between end diastolic coronary perfusion pressure and flow at peak hyperaemia was linear above 40 mmHg (group 1, n = 7) and became curvilinear at perfusion pressures below 40 mmHg (group 2, n = 7). At a mean left ventricular end diastolic pressure of 8.6(0.8) mmHg the mean zero flow intercept (P_int) in group 1 was 22.5(2.3) mmHg. Graded increases in left ventricular end diastolic pressure by infusion of blood resulted in a parallel rightward shift of the vasodilated pressure-flow relation (P_int = 1.06×LVEDP+13.8 mmHg, r = 0.87). The curvilinear relations at low perfusion pressures in group 2 had lower zero flow intercept pressures (P_int = 4.8(0.7) mmHg at left ventricular end diastolic pressure 6.6(1.5) mmHg). As with group 1, graded increases in left ventricular end diastolic pressure caused a rightward shift of the pressure-flow relation, with a direct relation between left ventricular end diastolic pressure and zero flow intercept (P_int = 0.93×LVEDP+3.9 mmHg, r = 0.89). Diastolic coronary pressure-flow relations during physiological vasodilatation are essentially linear at perfusion pressures >40 mmHg but are appreciably curved at lower pressures. Increases in left ventricular end diastolic pressure cause a parallel rightward shift of the linear region of the pressure-flow relation. Left ventricular diastolic pressure appears to be a major determinant of the zero flow intercept extrapolated from the curved low pressure region.