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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, which is the resistance in the pulmonary vasculature.
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Measurement
TPR is represented mathematically by the formula R = P/F. Where R is TPR, P is the change in pressure across the system vasculature, and F is the flow through the vasculature. In other words:
Total Peripheral Resistance = (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output
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. Methods of measuring Mean Arterial Pressure and Cardiac Output are described on the wiki pages for those respective topics.
Causes of Change in TPR
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 it osmolarity.
Peripheral Resistance is also dependent upon the capacitance of the blood vessel in through which the blood travels
See also
References
- An introduction to vascular biology [electronic resource] : from basic science to clinical practice / edited by Beverley J. Hunt ... [et al.]. Cambridge, UK ; New York : Cambridge University Press, c2002.
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