Wave Intensity Analysis in the Pulmonary Artery

The mechanism governing how blood flows from the heart to the lungs depends on many factors including the pumping function of the right ventricle, properties of the arteries that carry the blood from the right ventricle to the lungs (pulmonary arteries), and the lungs themselves. Under normal conditions the pressure in the pulmonary arteries is well controlled and significantly lower than in the systemic circulation, however there are a number of conditions that lead to abnormally high pressures and significant morbidity and mortality. However different patients respond differently to similarly elevated pressures, leading doctors to believe that there must be differences in either the right ventricles, the properties of the arteries, or the lungs themselves. It can be difficult to determine the relative contributions of each of these factors on blood flow because their effects are superimposed on each other. 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. This protocol aims to determine the major influences on blood flow in the pulmonary arteries in health and disease, to help to understand why some patients are affected more than others by elevated pulmonary pressures.