Page 7, Architecture of the Circulation, Dr. D. Penney
Circulation time is the average time taken for a particle in the blood (e.g. erythrocyte) to traverse a distance in the circulation. It could be the time required, for example, for a particle to traverse the systemic and pulmonary circulations and return to the starting point. The circulation time is shortest through the coronary bed (major source of the recirculation problem in measuring cardiac output by the Fick method), longer through muscle, kidney, etc., and longest through the spleen, where erythrocytes are stored and old or damaged ones are removed. The body average is 40-60 seconds at rest; approximately the blood volume or one cardiac output (5 liters) is circulated each minute.
Circulation time is decreased by exercise, arteriovenous shunting, and a reduction in venous pooling. For the average erythrocyte, most of the time is spent in the veins; thus, the circulation time is more dependent on what happens in the veins than in the arteries or arterioles (i.e. veno-motion vs. vaso-motion). As discussed earlier, circulation time is commonly determined by dye dilution technique.
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