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

Abstract

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.