One approach that has been used to look at this in other parts of the circulation (including in the systemic circulation and the coronary arteries) is to measure simultaneous pressure and flow, and apply a technique called wave intensity analysis (WIA). This technique can amongst other things, quantify the separate effects of wave reflection and the 'reservoir function' (or compliance) of the arteries, and in the systemic circulation WIA has increased the understanding of the mechanisms behind hypertension and the physiological changes of ageing. The pulmonary arteries are accepted to be very different from the systemic circulation and the mechanisms behind pulmonary hypertension are thought to be very different to those of systemic hypertension.