Consensus on Venous Hemodynamics in Primary Cvd

CONSENSUS ON VENOUS HEMODYNAMICSIN CHRONIC VENOUS DISEASE:

First part: Glossary

Rio de Janeiro 2005

World congress of UIP

C. Allegra, PL Antignani, A Cavezzi, P. Coleridge Smith, N. Labropoulos, P. Zamboni

Panel of experts:.Bergan, Brizzio,Cornu-Thenard,Cabrera, Cappelli, Comerota, De Simone, Eklof, Franceschi,Galeandro, Georgiev, Gloviczki, Grondin, Harada, Kistner, Junger, Lamasle, Mandolesi,Nicolaides, Partsch, Pepe, Pieri, Rabe, Ricci, Rosli, Schadeck, Staelens, Somejn, Van Rij, Vercelio, Vin.

Hydrostatic and ambulatory venous pressure

Pressure in the veins of the leg is determined by two main components, a hydrostatic component related to the weight of the column of blood corresponding to the hydrostatic pressure, and a hydrodynamic component related to 1-7 :

 pressure generated by contractions of the skeletal muscles of the lower limb muscular pump.

 the thoraco-abdominal pump activated by the respiratory mechanism

 residual venular pressure.

other pumps such as gluteal orfoot.

the vis a latere from the arterial pulse

These components are profoundly influenced by the action of the venous valves. During standing (without skeletal muscle activity) venous pressure in the leg is determined solelyby the hydrostatic component, because the valves are open.

We define as systole the skeletal muscle contractions directly compressing the veins, as during ambulation, and as diastole the subsequent phase of skeletal muscular relaxation 6. In muscular systole the proximal valves are open, and contraction increases the blood flow velocity within the deep leg veins. The corresponding velocities in the saphenous vein and sub-cutaneous tributaries are reduced. These haemodynamic effects are easily measurable in vivo using Doppler equipment. In muscular diastole, the valves are closed and the hydrostatic column becomes fragmented. Repeated contractions and relaxations, together with the synchronized opening and closing of valves,, lead to a progressive emptying of the deep venous system, accompanied by a substantial fall in deep venous pressure 8-10. This allows blood to flow from the superficial into the deep veins, and reduces the pressure in the superficial system. In the absence of competent valves and/or in the presence of obstruction in the deep veins, the deep venous pressure and volume fail to fall sufficiently with muscular exercise 1-10.

The relationship beween volume, pressure and diameter in veins.

The action of the valvulo-muscular pump, as described above, reduces both vein volume and pressure,11-13 When a vein is full, the relationship between vein volume and pressure (venous compliance) is linear 12-13. In contrast, during the filling phase, the volume/pressure relationship is not linear because an increase in volume produces little change in pressure. In filled veins, the linearity of the diameter/pressure relationship (Fig. 2) 17, or the relationship between residual volume (after exercise)/vein diameter has been established18. When vessel length is constant, volume and diameter are geometrically related because volume depends on the vein area and area is 1/4  D2. Vein diameter therefore reflects vein volume, with the former being easily assessed by the means of ultrasounds 14-20.

The linearity of these relationshipshas several implications:

-Increased diameter in a vein is related to the volume of blood.

-Changes in blood volume are related with changes in vein diameter, according to the compliance relationship.

-The relationship permits the extrapolation of useful parameters non-invasively.

Hierarchical order of emptying of the venous compartments of the lower extremity

The function of the venous system of lower limbs is to drain the blood toward the heart (cardiopete sense) whichever the direction of the venous pathways.

There are 3 anatomically and hemodynamically distinct compartments in the lower extremity: the superficial, the saphenous, and the deep 6,17,24-27. The borders of the compartments are outlined by the superficial and muscular fascia. These compartments will be termed as AC1 for the deep, AC2 for the saphenous, and AC3 for the superficial. Each anatomical compartment contains venous networks with different anatomical and functional significances. Network N1 represents deep veins located in AC1 compartment. Network N2 represents sub and intra-fascial superficial veins located in AC2 compartment (saphenoustrunks and Giacomini’s vein). Network N3 represents epi-fascial superficial veins located in AC3 compartment (saphenous tributaries and non-saphenous veins).

Finally, the pathways between different networks are defined by the network of connection (NC) such as perforators and any venous junctions.

In normal individuals the hierarchical order of emptying is from AC3 to AC2 or to AC1, or directly from AC3 to AC1. The hierarchical order of emptying is determined by a pressure gradient.

During standing the velocity in the veins is minimal and the highest intravenous pressure occurs beneath the longest hydrostatic column. As soon as the subject walks, the valvulo-muscular pump (VMP) of the lower limbs is activated. Alternate watertight closure of distal valves during systole of the valvulo-muscular pump, and proximal valves during the diastole, interrupts the liquid column, and reduces the overall the Hydrostatic Pressure. In addition, during muscular contraction there is increased blood flow velocity in the deep veins with a corresponding drop in the lateral pressure (Venturi’s effect). In contrast, distal pressure during systole is decreased by VMP. This creates a gradient among the veins in the different compartments.

All these mechanisms follow hydrodynamic laws but are not yet quantified in clinical practice.

According to the pressure gradient the flow is directed from AC3 and AC2 to AC1 through the perforator veins and the SFJ and SPJ. During muscular relaxation the valves are closed and the hydrostatic column in the compartments is fragmented.

Escape points

An escape point is a site of flow diversion between one compartment to another .

Reflux

Any retrograde flow in a vein can be defined as reflux. Reflux can be associated with or without an escape point (e.g. GSV reflux with or without incompetence of the terminal valve). Reflux is only the result of the gravitational forces.

In veins, reflux can be studied with many maneuvers. These are:

a)muscular-related maneuvers (active and passive). Muscular contraction allows assessment of the flow direction in muscular systole; muscular relaxation may produce opposite effects in muscular diastole. During relaxation in normal veins, the antegrade or retrograde flow will stop almost immediately as the valves close quickly.

b) compression of the varicose clusters.

c)Valsalva’s maneuver.

d)postural (positional) manouvres

Valsalva’s manoeuver is positive whenit induces reflux during abdomino-thoracic contraction, and negative if no flow is induced. During abdomino-thoracic relaxation, flow is initially increased before it becomes normal.

Hemodynamics of reflux in superficial veins and concept of re-entry.

Reflux may occurr as a “private circulation” starting at an escape point (EP) and ending the re-entry point(usually a re-entry perforating vein). In figure 11 an incompetent saphenous vein returnsblood from the sapheno-femoral junction (EP) to the deep veins of the calf through perforating veins (RP) (normal or abnormal) during the diastole. Thus, partof deep venous blood remains “excluded” from the general circulation in a “private circulation”.(insert reference of Trendelenburg).

Duration of reflux

The duration of reflux dependson vein diameter and on the capacity of the reservoir to be filled. The cut-off points for abnormal duration of reflux proposed for different sites are shown in Table I. Future research should establish quantitative criteria (volume/duration) of reflux.

. Table I summarizes the different values reported in literature for abnormal reflux.

GSV

SSV

Perforators

Femoral vein

Popliteal vein

Author

> 0.5 sec

> 0.5 sec

> 0.35 sec

> 1 sec

> 1 sec

Labropoulos

Interpretation of bidirectional flow in perforators

A normal perforator exhibits inward flow only: an outward flow indicates an abnormal perforator. However in abnormal perforating veins bidirectional flow (inward and outward flow) has to be investigated in detail. When the outward flow is present in diastole, this is considered reflux with an escape point; in contrast, when inward flow is present in diastole the perforator actsfunctionallyas a re-entry point to the deep veins.

At the moment, this working definition of venous dysfunction requires further refinements (concept of net flow by time, by quantification of flow, etc).

Development of reflux

The reason why veins become incompetent in primary CVD is unknown. There is significant evidence for a combination of valve pathologic fragility (venous wall disease) and excessive pressure conditions that render the affected (veins) valves incompetent. Such disease is most often seen in N3 and N2,especially in the GSV system. Most studies have shown that primary disease starts in the superficial veins and progresses into the perforator and deep veins. Reflux in the superficial veins progresses in an ascending and descending manner. It can be also isolated or multifocal. Reflux in the N3 and N2 as discussed above may affect the function of perforator and deep veins.

The incompetence diagnosis should be defined when an out flow , during the dynamic test, is detected. We can have a SYSTOLIC REFLUX (during the muscular contraction that engages the movement) and a DIASTOLIC REFLUX ( during the relaxation phase)

The SYSTOLIC REFLUX is typical for an INCOMPETENCE of a TERMINAL PERFORATOR (the lowest perforator along the hydrostatic column) without incompetence of the deep veins.

The DIASTOLIC REFLUX is typical for an INCOMPETENCE of a NON-TERMINAL PERFORATOR (the perforators placed along the hydrostatic column).

The SYSTO-DIASTOLIC REFLUX is typical for an INCOMPETENCE of a PERFORATOR with incompetence or obstruction of the deep veins.

The re-entry concept should be correlated with the function of perforators that is the blood drainage in the deep system during the systolic and diastolic phase.

In an incompetent terminal perforator (re-entry perforator) a systolic reflux can be detected. But if the quantity of blood that renters during the diastolic phase is higher than that which comes out during the systolic phase, the perforator can be defined as incompetent but sufficient to develop its function. As demonstrated by the tourniquet test where we can see the varicose veins emptying even if a systolic reflux through the perforators is detectable. It depends on the quantity of blood that comes out in relation to the quantity that renters.

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