The venous return simulator: comparison of simulated with measured ambulatory venous pressure in normal subjects and in venous valve incompetence.

BACKGROUND: To compare results of numerical simulation of lower limb venous return with those of in vivo measurements, in normal subjects, and those with venous incompetence. PATIENTS AND METHODS: the venous return simulator (VRS) is a mathematical model which takes into account architecture, dimensions, and compliance of the venous network, blood viscosity, valve function, and external pressures (muscular contraction, compression stockings). Using the laws of hydrodynamics, it provides calibres, pressures and flows throughout the network. Ambulatory venous pressure (AVP) computed for some theoretical examples of superficial and /or deep venous incompetence has been compared to in vivo values reported in literature. RESULTS: In a normal subject, computed AVP was 33 mmHg during walking and 30 mmHg with tiptoe exercise; the range of conventionally measured AVP is 20.6 - 27.9 mmHg during walking, and 29 - 32.5 mmHg during tiptoe exercise; In the case of great saphenous vein (GSV) incompetence, computed AVP was 34 or 57 mmHg, according to whether the distal GSV was competent or not. The range of AVP measured in superficial venous insufficiency is 27.6 - 61 mmHg, all but one of the published values lie between the low computed value corresponding to a short reflux and the high computed value due to a long distance reflux. AVP computed in two cases of deep venous incompetence was 44 and 71 mmHg, according to the extent of devalvulation, as compared with the 60 mmHg reported in one clinical study In patients with extensive combined incompetence, computed AVP was 75 mmHg, whilst the range of conventionally measured values was between 62 and 84 mmHg. CONCLUSIONS: the good agreement between computed and measured AVP in different cases of valve incompetence indicates that the VRS is quite a realistic model, with the potential to simulate the results of surgery or compression therapy.

[Digital simulation of venous and lymphatic edema and the effects of compression]. / Simulation numérique de l'œdème veinolymphatique et des effets de la compression.

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.