Figure 18-8 Illustration demonstrating the principle of determination of cardiac output by using the indicator dilution technique. This model assumes that there is no recirculation. A known amount of dye (q) is injected at point A into a stream flowing at (mL/min). A mixed sample of the fluid flowing past point B is withdrawn at a constant rate through a densitometer. The change in dye concentration over time is depicted in a curve. Flow may be measured by dividing the amount of indicator injected upstream by the area under the downstream concentration curve. (From Berne RM, Levy MN: The cardiac pump. In Cardiovascular Physiology, 8th ed. St Louis, CV Mosby, 2001, pp 55–82.)