Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system. The resistance offered by the systemic circulation is known as the systemic vascular resistance (SVR) or may sometimes be called by the older term total peripheral resistance (TPR), while the resistance offered by the pulmonary circulation is known as the pulmonary vascular resistance (PVR). Vasoconstriction (i.e., decrease in blood vessel diameter) increases resistance, whereas vasodilation (increase in diameter) decreases resistance. Blood flow and cardiac function is related to blood pressure and inversely related to vascular resistance.