Effect of Vasomotor Tone on Coronary Flow Impediment in Systole

Summary

We have studied the effect of cardiac contraction on coronary arterial flow, in the isolated blood-perfused donor-supported rat heat, with vasomotor tone present and after maximal vasodilation with adenosine (n = 6). A balloon in the left ventricle made it possible to change ventricular volume and thus pressure at a constant contractile state. Extra systolic potentiation was used to change cardiac contractility. Coronary pressure and flow measurements were performed at constant vasomotor tone as judged from stable diastolic coronary flow. The effects of developed left ventricular pressure, i.e., systolic minus diastolic pressure (devP_lv, in mmHg) and developed ventricular elastance i.e., systolic minus diastolic elastance (devE_lv, in mmHg/ml) on coronary blood flow (CBF) amplitude defined as diastolic minus systolic flow (ΔCBF, in ml/g.min) were determined through multiple regression of the form: ΔCBF = Sp.devP_lv + S_E-devE_er + I, with S_P in ml/(g.min.mmHg), S_E in ml²/(g.min.mmHg) and I in ml/(g.min). In the control vasoactive state we found (mean ± SD): ΔCBF = (0.015 ± 0.005) devP_lv + (0.0026 ± 0.014) devE_lv + (0.19 ± 0.60). Maximal vasodilation increased coronary flow in diastole by a factor of 4.06 ± 0.70. The sensitivity to devP_lv and devE_lv increased by a factor of 5.40 ± 3.35 and 4.23 ± 0.61, respectively. These factors were not different. We therefore conclude contrary to the findings in the cat and rabbit and dog heart that left ventricular pressure has an effect on coronary flow impediment during maximal vasodilation and that vasodilation increases diastolic flow and the coronary flow amplitude by a similar factor.