Total peripheral resistance
Template:WikiDoc Cardiology News Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Total peripheral resistance refers to the cumulative resistance of the thousands of arterioles in the body, or the lungs, respectively. It is approximately equal to the resistance of the arterioles, since the arterioles are the chief resistance vessels in the body.
Peripheral resistance occurs when arterioles are unable to completely relieve pressure in the arteries. When the heart contracts, blood enters the arteries faster than it can leave, and the arteries stretch from the pressure. Although the vessels return to their normal state during diastole, the heart will contract again before all the blood has completely flowed into the arterioles. This inhibits the arterioles' ability to fully relieve the pressure in the arteries, causing peripheral resistance.
Total Peripheral Resistance = Mean Arterial Pressure / Cardiac Output
The total peripheral resistance of healthy lung arterioles is typically about 15 to 20 percent that of the body, so pulmonary artery mean blood pressures are typically about 15-20% of aortic mean blood pressures.
As a consequence of the arteries being forced to work against peripheral resistance, there is substantial blood pressure even during diastole. Arterioles are sometimes referred to as resistance vessels because of their peripheral resistance.