CONSENSUS ON VENOUS HEMODYNAMICS IN 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 or foot.
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 solely
by 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
established 18. 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 relationships has 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 (saphenous trunks and Giacomini’s vein). Network N3 represents epifascial superficial veins located in AC3 compartment (saphenous tributaries and nonsaphenous 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 valvulomuscular 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 when it 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 returns blood from the sapheno-femoral junction (EP) to the deep veins of
the calf through perforating veins (RP) (normal or abnormal) during the diastole. Thus,
part of deep venous blood remains “excluded” from the general circulation in a “private
circulation”.(insert reference of Trendelenburg).
Duration of reflux
The duration of reflux depends on 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
> 0.5 sec
> 0.5 sec
> 0.35 sec
Femoral
vein
> 1 sec
Popliteal
vein
> 1 sec
Author
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 acts functionally as 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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