Capillary filtration pressure


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Capillary filtration pressure

  1. 1. Understanding Capillary Filtration Pressure Casey Christy, MA, ATC, CSCS
  2. 2. Key Terms • Capillary Hydrostatic Pressure (CHP): pressure exerted by water in the blood which forces fluid out of the capillary • Tissue Hydrostatic Pressure (THP): pressure that forces fluid back into the capillary
  3. 3. Key Terms • Capillary Oncotic Pressure (COP): pressure that pulls fluid back into the capillary • Tissue Oncotic Pressure (TOP): pressure that pulls fluid out of the capillary as a result of free proteins attracting fluid Note that “oncotic pressure” is also known as “colloid osmotic pressure”
  4. 4. Sum of Forces • Capillary Filtration Pressure (CFP) is expressed as an equation: • CFP= (CHP+TOP) – (THP+COP)
  5. 5. Capillary Filtration PRessure • Here it is again spelled out: Capillary Filtration Pressure = (Capillary Hydrostatic Pressure + Tissue Oncotic Pressure) minus (Tissue Hydrostatic Pressure + Capillary Oncotic Pressure)
  6. 6. Capillary Filtration PRessure • The sum of these forces that make up CFP determines which way fluid travels and is also known as “Starling Forces” • Normal (non-injured) CFP is slightly positive
  7. 7. Starling Forces Tissue Oncotic Pressure Capillary Hydrostatic Pressure Tissue Hydrostatic Pressure Capillary Tissue Capillary Oncotic Pressure
  8. 8. Capillary Filtration PRessure • Hydrostatic forces “push” fluids • Oncotic forces “draw” fluids
  9. 9. Capillary Filtration PRessure • CHP is normally positive at the arteriolar end of the capillary, causing fluid to move out of the capillary and into the tissue • At the venular end of the capillary, forces are different to allow resorption of fluid back into the capillary
  10. 10. When Injury Occurs • When an injury occurs Capillary Filtration Pressure (CHP) changes as a result of increased Tissue Oncotic Pressure (TOP), causing edema accumulation in the tissue • Read on to see why…
  11. 11. When Injury Occurs • When an injury occurs, free proteins escape into the tissue as a result of increased capillary permeability, tissue debris, or blood vessel bleeding • This increases Tissue Oncotic Pressure (TOP) which draws fluid into the tissue resulting in edema and
  12. 12. When Injury Occurs • Normally (no injury), 2/3 of the fluid leaving the capillary is reabsorbed into the capillary, and the rest is picked up by the lymphatic system • With an injury, this system is overloaded since more fluid is exiting the capillary than can be absorbed
  13. 13. When Injury Occurs • In summary, capillary filtration pressure increases when an injury occurs, leading to fluid buildup in the tissues
  14. 14. Reference • Knight and Draper, Therapeutic Modalities: The Art and Science