A measure of the opposition encountered by the blood as it flows through blood vessels. It is the sum of all the regional individual resistances to arterial blood as it passes through the many and varied circuits to body organs and tissues. Peripheral resistance is caused by friction between the blood and the walls of blood vessels. It varies inversely to the fourth power of the radius of the vessel. Thus, if the radius is halved, resistance increases 16-fold enabling substantial blood flow changes to be effected by relatively small adjustments to the radius of the vessels (see shunting). Peripheral resistance is an important indicator of cardiovascular fitness. Physical training can favourably and significantly lower total peripheral resistance, reducing the load on the heart.
Subjects: Sports and Exercise Medicine.