A measure of the total resistance to blood flow provided by the entire vascular system.
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A measure of the total resistance to blood flow provided by the entire vascular system.
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Vasculature throughout the entire body can be thought of as two separate circuits - one is the systemic circulation, while the other is the pulmonary circulation. Total peripheral resistance (TPR) is the sum of the resistance of all peripheral vasculature in the systemic circulation. This should not be confused with Pulmonary Vascular Resistance (PVR), which is the resistance in the pulmonary circulation.
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TPR is represented mathematically by the formula R = ΔP/Q.
In other words:
The numerator can be seen as representing the change in pressure that occurred immediately after having left the heart (i.e., mean arterial pressure) to when it finally returned to the heart via the IVC to the right atrium (i.e., mean venous pressure).
Mean Arterial Pressure (MAP) is the average of the aortic systolic and diastolic pressures.
Mean Venous Pressure is measured at the right atrium and is usually very low (normally around 4mm Hg). As a result, it is sometimes disregarded. A synonymous term is central venous pressure.
Peripheral resistance increases due to binding of norepinephrine and epinephrine to the α1 receptor on vascular smooth muscles. These hormones cause vasoconstriction, thus decreasing the radius of the vessels in the periphery. Resistance is inversely proportional to radius^4. Thus, a decreased radius will greatly increase the resistance.
Peripheral Resistance is also affected by the viscosity of the blood flowing through it. The viscosity of blood is normally associated with its osmolarity.
Peripheral Resistance is also dependent upon the capacitance of the blood vessel in through which the blood travels
An decrease in TPR(eg. during exercising) will result in an increased flow to tissues and an increased venous flow back to the heart. An increased TPR will decrease flow to tissues and decreased venous flow back to the heart.
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![]() | Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more | |
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