TPR Basics

• Total Peripheral Resistance:

  • Resistance in this context basically means opposition to flow
  • The main opposition or resistance to blood flow is due to the friction that blood encounters as it passes through a vessel
  • Most friction is caused by blood interfacing with the vessel wall endothelium
  • The majority of resistance occurs in the systemic (peripheral) vessels at the level of the arterioles, hence the term total peripheral resistance
• Total Peripheral Resistance:

  • There are 3 important determinants of total peripheral resistance i.e. factors that affect the amount of friction encountered:
  • Blood viscosity
  • Vessel length
  • Radius of the blood vessel
  • These factors are unified in POISEUILLES LAW:
  • R = L8n / pi x r^4 - DONT NEED TO KNOW
  • A basic interpretation of the equation tells us that resistance is
  • proportional to vessel length & blood viscosity
  • & inversely proportional to the 4th power of the radius