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Peripheral resistance is the resistance of the arteries to blood flow. As the arteries constrict, the resistance increases and as they dilate, resistance decreases.

Peripheral resistance is determined by three factors:

  1. Autonomic activity: sympathetic activity constricts peripheral arteries.
  2. Pharmacologic agents: vasoconstrictor drugs increase resistance while vasodilator drugs decrease it.
  3. Blood viscosity: increased viscosity increases resistance.