Non-stationary theory of blood-borne tracers.

Although cardiac mechanical activity causes periodic fluctuations of the regional volumes and flows through the cardiac chambers and great vessels, hitherto, the developed theory of blood-borne tracers has rested upon stationarity of flow, volume and distribution of transit time. Allowing for an arbitrary indicator injection, a more general theory is presented that accounts for periodic changes in the transport laws, flows and volumes of the system. When indicator particles are not thoroughly mixed with the entering blood, the intracycle changes violate most of the stationary equations. However, assuming complete mixing of indicator at the system inlet, in concentrations that do not change during the single cycle, this enables generalized counterparts of some of the most important stationary relations to be established. The difference between the indicator mean transit time calculated from the stationary assumptions and the one which allows for periodic kinetics is illustrated in radioangiographic assessment of the left ventricular ejection fraction.