The use of artificial schemata for teaching the mechanical principles of the circulation is properly considered one of the most valuable of our laboratory methods.
As arterial pressure—the driving force of the blood— is a function of three variables, the output of the pump, vascular elasticity and peripheral resistance, when these factors are known, the calculation of the blood velocity and blood pressure in any part of the vascular circuit would appear to be a matter of gratifying simplicity. But when we study the hemodynamics of the living animal, especially when in clinical work the vascular apparatus departs more or less from normal, deductions made from principles established by the use of artificial machines will lead us far astray from the truth. The error involved is not in the teachings of the schema as a schema, but in our poor logic in trying to measure the workings of a very
SEWALL H. EXPERIMENTS ON VENOUS BLOOD PRESSURE AND ITS RELATIONS TO ARTERIAL PRESSURE IN MAN. JAMA. 1906;XLVII(16):1279–1289. doi:10.1001/jama.1906.25210160043001n
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