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Osmotic flows across the blood-joint barrier
1Department of Physiology, St George's Hospital Medical School, London.
Annals of the Rheumatic Diseases
|July 1, 1987
Summary
Plasma colloid osmotic pressure (COP) controls synovial fluid. Albumin COP effectively drives fluid absorption across the blood-joint barrier, while small solutes are less effective. Joint fluid absorption is linearly related to plasma COP.
Area of Science:
- Physiology
- Biophysics
- Rheumatology
Background:
- The blood-joint barrier regulates synovial fluid volume and joint effusions.
- Plasma colloid osmotic pressure (COP) is a critical factor influencing fluid dynamics within joints.
Purpose of the Study:
- To directly investigate the impact of plasma COP on trans-synovial fluid flow in rabbit knees.
- To quantify the effectiveness of albumin and small solutes in driving osmotic flow across the blood-joint barrier.
Main Methods:
- Directly perfusing the synovial microcirculation of rabbit knees with blood of varying COP.
- Infusing intra-articular fluid to expand joint volume.
- Measuring trans-synovial flow in response to altered plasma COP and intra-articular pressures.
Main Results:
- Joint fluid absorption demonstrated a linear correlation with plasma COP.
- Albumin's COP was 78% as effective as expected across the blood-joint interface.
- Hyperosmolar solutions of small solutes, like glucose, induced transient osmotic flows but were significantly less effective than albumin.
- Synovial hydraulic permeability increased under pathological intra-articular pressures.
Conclusions:
- Plasma COP is a primary determinant of synovial fluid absorption.
- Albumin is a key driver of fluid movement across the blood-joint barrier, though with reduced efficacy.
- The increased hydraulic permeability of synovium at high pressures may contribute to joint effusion kinetics.