The authors’ reply: We are grateful to Drs Murakami and Morimoto for their insightful comments about our recent publication1 on the importance of aortic reservoir in directing coronary blood flow. We agree that preservation of coronary blood flow depends on a delicate balance between the aortic driving pressure,2 and the run-off of blood through the myocardium into the coronary microcirculation. Experimental data show that for much of systole, coronary blood flow is relatively sluggish (5–10 cm/s) and that it is not until diastole, when pressures at the microcirculatory end of the coronary artery fall at a significantly faster rate than those in the aorta, that blood flow is markedly increased.

Using new techniques such as wave intensity analysis, it is possible to observe and systematically quantify these changes in pressure (fig 1), and observe the waves directing coronary flow.3 4 Such techniques in combination with aortic reservoir pressure analysis may well provide further insight in situations, such as those outlined by the Murakami and Morimoto, when disease states can coexist at both the aortic and myocardial ends of the coronary artery.

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Figure 1

Separation of pressure into proximal and distal originating components in the left anterior descending artery. Pressure was separated into proximal and distal originating pressure by wave intensity analysis. During systole, blood flow is low as proximal and distal originating pressures are approximately equal and it is only during diastole, when distal originating pressure falls markedly, that blood flow increases significantly.