Pulmonary arterial wave intensity analysis in health and disease.

Wave intensity analysis (WIA) is a time-domain technique utilising high fidelity pressure and velocity measurements to determine the intensity, direction, type and timing of waves that may simultaneously exist. Travelling wavefronts represent elemental units of energy transmitted within and between the heart and blood vessels. Thus, WIA allows us to study ventricular-arterial interactions providing information on ventricular performance and the state of the circulation. In the pulmonary circulation WIA allows the study of upstream and downstream events that influence net pulmonary arterial blood flow. WIA was performed in the pulmonary arteries of anaesthetised open-chest sheep, determining a normal mean wave speed of 2.1 ms-1. Whilst wave reflection was minimal in healthy resting pulmonary arteries, two minor but clearly discernible backward travelling waves were identified that serve as important physiological markers. The first was an early systolic backward expansion wave representing open-end reflection from a site approximately 3 cm downstream, most likely from the main pulmonary bifurcation, and would serve to augment flow out of the right ventricle. The second was a late systolic backward compression wave representing closed-end reflection from a site approximately 20 cm downstream, most likely from the pulmonary microcirculation, and would serve to oppose flow out of the right ventricle. The open-end reflection was enhanced by increased pulmonary blood flow or circulating blood volume. With pulmonary vasoconstriction or obstruction, WIA was able to accurately determine the distance to the newly developed closed-end reflection site from which a backward compression arrives in mid-systole and opposes flow out of the right ventricle. In human volunteers with normal or diseased pulmonary vasculature, wave speed was shown to increase linearly with pulmonary vascular resistance. The difficulties in reproducing instantaneous pulmonary blood velocity accurately invivo limited assessment of reflected waves.