Coronary Pressure-Flow Relation in Excised Canine Heart

We investigated the change in the instantaneous diastolic left coronary pressure-flow relation (DPFR) when the pressure surrounding the heart (SHP), right heart pressure (RHP), and left heart pressure (LHP) were systematically varied. Eight excised and maximally vasodilated canine hearts placed in an air-tight chamber were used. To obtain a capacitance-free DPFR, coronary perfusion pressure was slowly decreased (about 2 mm Hg/sec) during a prolonged diastole . The zero-flow pressure (Pf = 0) and the slope of the DPFR were analyzed. The mean values of the slope did not change significantly throughout the interventions. The mean value of Pf=0 in the control state (SHP = RHP = LHP = 0 mm Hg) was 6.0±2.0 mm Hg (mean±SD, n = 8), significantly higher than the venous outflow pressure, RHP (p<0.00l), and the other two pressures (p<0.00l). When SHP was raised to 15 and 30 mm Hg, while the other pressures remained at 0 mm Hg, the mean values of Pf=0 increased to 20.9 ±2.4 and 35.6 ±3.1 mm Hg (p<0Ml and /?<0.0005, respectively, vs. control). The mean values of Pf = 0 when only RHP was elevated to 15 and 30 mm Hg were 16.0±1.5 and 29.3±1.5 mm Hg (p<0.001 and /;<0.0005 vs. control). On elevation of LHP to 15 and 30 mm Hg, the mean values of Pf = 0 were 12.0 ±2.8 and 17.3±3.6 mm Hg (p<0.0l and p<0.01 vs. control). When both SHP and LHP were almost evenly elevated to about 15 and 30 mm Hg, the mean values of Pf = 0 were raised to 22.0 ±2 .9 and 35.3 ±3.2 mm Hg, respectively. These mean values were not significantly different from those when only SHP was elevated to the comparable levels. The observation that Pf = 0 exceeded RHP in the control state and that RHP, which was elevated above the preceding Pf=0, was identical with the present Pf=O supports the vascular waterfall mechanism when RHP is low. Furthermore, the evidence that the degree of DPFR shift was almost linearly dependent on the SHP level rather than on the LHP level indicates that the pressure on the epicardial side is one of the factors that determines the pressure at the top of the vascular waterfall. (Circulation Research 1988;63:788-797)