Fig. (1).

Difference between the pressure-flow relationship in systemic and coronary arteries. It can be seen that in a systemic artery changes in pressure and flow closely follow each other. In systole they both increase whilst in diastole they both decrease (upper panel). In the coronary circulation (lower panel) this is not the case. After an initial period in systole when pressure and flow increase together, flow velocity plateaus whilst pressure continues to increase. In early diastole it can be seen that pressure falls rapidly whilst flow velocity increases. Such a paradoxical relationship in early diastole cannot be explained by the traditional haemodynamic model of the systemic vessel.