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One way to measure cardiac output (in l/min) is to inject a small quantity of dye (usually indocyanine green - ICG) into the venous blood stream close to the heart through a catheter. The dye mixes with the blood, and a sample of arterial blood is drawn off through another catheter and passed through an optical densitometer to detect the concentration of dye. The concentration rises rapidly and then falls. The rate at which blood passes through the heart can be calculated from the area under the curve of concentration and a knowledge of the quantity of dye introduced.
This is an invasive method and the dye is slightly toxic and so it is normally used in conjunction with other invasive procedures during cardiac catheterization in the cardiac catheter laboratory.
The apparatus consists of a high-speed motorized syringe pump, a densitometer sensitive to transmission at 805 nm (for ICG), and a small computer.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details