The effects of the coronary capacitance on the interpretation of diastolic pressure- flow relationships

SUMMARY. The effects of coronary capacitance on instantaneous pressure-flow (P/F) relationships were analyzed using a theoretical model of coronary flow during diastole that included capacitance. The magnitude of the discrepancy between actual intramural and instantaneously derived P/F relationships was predicted to be dependent on the ratio of two natural decay constants (central aortic decay constant/intrinsic coronary decay constant). The effects of coronary capacitance are eliminated using constant pressure conditions. The instantaneous (dynamic) and constant pressure (static) P/F relationships were compared experimentally using a reservoir to provide constant pressure perfusion during prolonged diastoles in heart blocked dogs. In the presence of coronary tone, zero flow pressure intercepts (P) ̂ of 27.1 ± 6.6 and 11.0 ± 3.0 mm Hg were obtained under dynamic and constant pressure conditions respectively, P < 0.001. After maximal vasodilation,??s of 14.2 ± 4.5 mmHg and 10.7 ± 2.4 mmHg were obtained under dynamic and constant pressure conditions, respectively, P = NS. Pzf derived under constant pressure conditions were independent of the state of coronary vasomotor tone with a value about 11 mmHg. The slopes of the dynamic P/ F relationships tended to be greater than those derived from constant pressure conditions. This may suggest an additional component of increasing coronary resistance during diastole that could not b