Quantitation of changes in lymph protein concentration during lymph node transit

Area of Science:

• Physiology
• Lymphatic System Biology
• Fluid Dynamics

Background:

• Investigator assumption: interstitial fluid and lymph protein concentrations are identical post-lymph node.
• Lack of quantitative data on lymph node modification of lymph.

Purpose of the Study:

• Quantify lymph modification by the popliteal lymph node in dogs.
• Compare prenodal and postnodal lymph protein concentrations and colloid osmotic pressure.

Main Methods:

• In situ perfusion of isolated dog popliteal lymph nodes at physiological flow rates.
• Infusion of homologous plasma or diluted plasma to assess fluid and protein transfer.
• Direct comparison of prenodal and postnodal lymph parameters.

Main Results:

• Lymph nodes actively modify lymph protein concentration and colloid osmotic pressure via fluid transfer.
• Dilution observed with undiluted plasma infusion; concentration with diluted plasma.
• Nearly all changes (98%) explained by protein-free fluid transfer.
• No lymph modification occurred at an "equilibrium colloid osmotic pressure" (60% of plasma).
• Concentrating-diluting mechanism intensified with decreased perfusion rate or deviation from equilibrium pressure.

Conclusions:

• Lymph nodes modify lymph protein concentration and colloid osmotic pressure unless equilibrium is met.
• The assumption of postnodal lymph representing interstitial fluid is likely incorrect, particularly at low physiological lymph flows.