Page 20, hemodynamics, Dr. D. Penney
Vascular resistances come in many forms, and may be roughly divided into "functional", "fixed", and "passive" types. Functional resistance is that resistance which can be altered by the contraction or relaxation of vascular smooth muscle. Fixed resistance is due to arteriosclerosis, coarctation, shunts, etc. Passive resistances, on the other hand result for example from changes in vessel caliber due to decreased transmural pressure (arm over head) or to the pressure of organ or bone weight on a blood vessel.
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