Venous flow restriction: the role of vein wall motion in venous admixture.

OBJECTIVE: There are wide differences in flow between vascular beds at rest, even more during stress. The hydrodynamic energy (Energy grade line or EGL) of venous outflows must also vary considerably between vascular beds. We explored the mechanism of venous admixture of differing energy flows using a mechanical model. MATERIALS AND METHODS: The model simulated two venous flows coalescing at a venous junction and then flowing through collapsible venous pumps. Flow rates and pressures were monitored when the venous pumps were full (steady state) and when they were compressed and allowed to refill inducing wall motion (pump flow). RESULTS: With increasing EGL differences between two coalescing venous flows, reduction or cessation (venous flow restriction) of the weaker flow occurred during steady state; higher base EGL of both flows ameliorated venous flow restriction and lower base EGL the opposite. Outflow obstruction favoured venous flow restriction. Pump action in the vicinity of the venous junction abolished venous flow restriction and maximized both venous flows. CONCLUSION: The model suggests a pivotal role for vein wall motion in venous admixture and regional perfusion. Observations in the model are explained on the basis of network flow principles and collapsible tube mechanics.

Venous valve station changes in "primary" and postthrombotic reflux: an analysis of 149 cases.

The purpose of this study was to analyze valve station changes noted during venous valve reconstruction and the associated outcome. One hundred and forty-nine valve reconstructions were available for analysis at the time of surgical exploration; the venous valve was graded according to valve station changes (VS grades) from zero through six. Ascending venography was analyzed by a similar grading system and the two methods were compared. The results of this analysis showed that valve station wall changes are frequently present in patients with deep venous reflux and pose technical challenges during valve reconstruction; the outcome, however, appears unaffected. Grade 0 to 1 valve station changes are predominantly due to "primary" reflux, with an occasional instance of postthrombotic etiology. Grade 2 or 3 valve station changes are roughly evenly divided between phlebosclerosis of primary reflux and postthrombotic etiologies. The mechanism of onset of reflux with preservation of valve cusps in the latter group of postthrombotic cases is probably different from currently accepted theories of evolution of postthrombotic changes. Postthrombotic valve damage is variable, and the valve station anatomy may be sufficiently preserved in some patients to allow direct valve repair.

Saphenectomy in the presence of chronic venous obstruction.

BACKGROUND: The results of saphenectomy in patients with morphologic and functional obstruction were compared with those in patients without obstruction. Excision of secondary saphenous varices associated with deep venous obstruction has long been considered contraindicated for fear of compromising its collateral contribution. Recent advances in accurate functional assessment of venous obstruction make it possible to test this concept. METHODS: Saphenectomy was carried out in 51 limbs without morphologic or functional obstruction and 64 limbs with varying grades of venous obstruction. Significant deep venous obstruction on ascending venography was present in the latter group. Functional assessment of obstruction was based on the arm/foot venous pressure differential technique, outflow fraction measurements, and outflow resistance calculations. Valve reconstruction was carried out in conjunction with saphenectomy in 81% of cases. RESULTS: Saphenectomy was clinically well tolerated in both groups, and there was no difference in outcome as measured by objective tests for obstruction; improvement in reflux and calf venous pump function was largely similar. Among seven limbs with severe preoperative venous obstruction (grade III or IV), five (70%) had significantly improved obstructive grading, presumably as a result of elimination of reflux flow. CONCLUSIONS: The traditional admonition against removal of secondary varices should be reexamined. Saphenectomy may be indicated in postthrombotic syndrome with mixed obstruction/reflux. The procedure is clinically well tolerated and without malsequelae. Improvement in reflux parameters without significant worsening of objective measures of obstruction is documented in this group.

Tube collapse and valve closure in ambulatory venous pressure regulation: studies with a mechanical model.

PURPOSE: To determine the role of valve closure and column segmentation in ambulatory venous pressure regulation. METHODS: Using a mechanical model consisting of a graduated adjustable valve and a collapsible tube, we studied the differential effects of valve closure and tube collapse on venous pressure regulation. By utilizing materials with differing wall properties for the infravalvular tube, the influence of wall property changes on tube function and pressure regulation was explored. RESULTS: Valve closure, per se, does not cause venous pressure reduction. Collapse of the tube below the valve is the primary pressure regulatory mechanism. The nonlinear volume-pressure relationship that exists in infravalvular tubes confers significant buffering properties to the collapsible tube, which tends to retain a near-constant pressure for a wide range of ejection fractions, residual tube volumes, and valve leaks. Changes in tube wall property affect this buffering action, at both the low and high ends of the physiological venous pressure range. CONCLUSIONS: The valve and the infravalvular venous segment should be considered together in venous pressure regulation. Tube collapse of the segment below the valve is the primary pressure regulatory mechanism. An understanding of the hydrodynamic principles involved in pressure regulation derived from this model will provide the basis for construction of more complex models to explore clinical physiology and dysfunction.

Durability of venous valve reconstruction techniques for "primary" and postthrombotic reflux.

PURPOSE: The durability of the variety of valve reconstruction techniques in "primary" reflux and postthrombotic reflux was studied. METHODS: A total of 423 valve repairs in 235 patients with a follow-up period ranging from 1 to 12 years were analyzed. End points for assessment consisted of ulcer recurrence and Doppler competence in serial duplex examination. Multivariate analysis with Cox proportional hazards model was used. RESULTS: Ulcer-free survival curves were similar for "primary" and postthrombotic reflux. No significant difference in ulcer recurrence was seen regardless of the technique used. Different results were obtained when valve competence instead of ulcer recurrence was used for assessment of durability. Reconstructions in "primary" reflux were more durable than those in postthrombotic reflux. Durability differences were also noted among different techniques. A cohort of posterior tibial repairs proved extraordinarily durable (0 failures in 23 repairs). CONCLUSION: Valve reconstruction in postthrombotic reflux can yield clinical results similar to those in "primary" reflux. Although any of the several described techniques can produce similar clinical results, Doppler competence suggests the following order for choice of procedures: (1) internal valvuloplasty, (2) prosthetic sleeve in situ, (3) external valvuloplasty, and (4) axillary vein transfer.