[Digital simulation of venous and lymphatic edema and the effects of compression]

Compression therapy for venous and lymphatic edema of the lower limbs raises a major challenge concerning the optimal pressure ensuring both efficacy and patient compliance. We present a mathematical model of tissue fluid transfers which is aimed at determining the lowest pressure required to prevent edema.

The model is based on a set of equations, derived from published experimental data, which describe the fluid and solute transfers between blood, interstitium and lymphatics, and the mechanical properties of interstitial compartment. It enables us to compute the changes in tissue volume, at the ankle level, resulting from increases of capillary pressure in case of venous insufficiency, and from an impairment of lymph drainage; as well as the effect of various external pressures upon this volume.

An increase of capillary pressure to 40 and 50 mmHg results in an ankle edema which is completely prevented by an external pressure of 10 mmHg. This result is in keeping with the observation by Partsch that vesperal leg swelling is reduced by low compression stockings. The dose effect reported in this study is also found by simulation. The complete blockade of lymphatic return leads to an edema, the prevention of which requires a counterpressure of at least 30 mmHg. When an increase of venous pressure to 60 mmHg, and a reduction by 2/3 of lymphatic drainage are combined, simulating chronic venous insufficiency, the resulting edema is prevented by a 25 mmHg counterpressure.

These first results of simulation are in reasonable agreement with clinical experience. As nearly every combination of disturbances may be simulated, the computer model could help to understand and treat edemas, as long as their cause can be identified.