Vascular Resistance

Vascular resistance is a term used to define the resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance (SVR), while the resistance offered by the vasculature of the lungs is known as the pulmonary vascular resistance (PVR). The systemic vascular resistance may also be referred to as the total peripheral resistance. Vasoconstriction (i.e., decrease in blood vessel diameter) increases SVR, whereas vasodilation (increase in diameter) decreases SVR.

Units for measuring vascular resistance are dyn·s·cm−5, pascal seconds per cubic metre (Pa·s/m³) or, for ease of deriving it by pressure (measured in mmHg) and cardiac output (measured in l/min), it can be given in mmHg·min/l. This is numerically equivalent to hybrid reference units (HRU), also known as Wood units, frequently used by pediatric cardiologists. To convert from Wood units to MPa·s/m3 you must multiply by 8, or to dyn·s·cm−5 you must multiply by 80.