We examined the 'vascular waterfall' hypothesis, which proposes that coronary flow is unaffected by elevations in outflow pressure until the latter reaches a critical threshold level, in 29 isolated canine hearts. In fibrillating hearts vasodilated with adenosine or carbocromen, coronary flow and the coronary pressure-flow relation were not affected by changes in great cardiac vein pressure (P(GCV)) below a threshold value of 11±0.9 (mean ± SEM) mm Hg. Further elevations of P(GCV) reduced flow and shifted the pressure-flow relation to the right, increasing its pressure-axis intercept (P(f=0)). When vasomotor tone was augmented with vasopressin, threshold P(GCV) increased to 25±2.7 mm Hg (p<0.001). Once again, the pressure-flow relation was unaffected by changes in P(GCV) below the threshold value and shifted to the right when this value was exceeded. The amount by which spontaneous values of P(f=0) exceeded threshold values of P(GCV) was greater when vasomotor tone was augmented than during vasodilation. P(f=0) continued to exceed P(GCV) when the latter was raised above the threshold level. Both P(f=0) and threshold values of P(GCV) were less during a long diastole than during ventricular fibrillation. We reached the following conclusions. 1) During changes in P(GCV) below a threshold value, the coronary circulation exhibits traditional waterfall behavior. 2) The threshold pressure for altering waterfall behavior is affected by vascular tone and mechanical activity. 3) P(f=0) remains above P(GCV) when the latter is increased above the threshold value needed to alter flow.
- coronary pressure-flow relations
- vascular waterfall
- zero-flow pressure
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine