Venous Lymphedema

In the article, "Diagnosis and Treatment of Venous Lymphedema", Raju et al describe the phenomena of primary and secondary lymphedema.

http://www.jvascsurg.org/article/S0741-5214(11)01833-7/pdf

Primary lymphedema is congenital and is present from birth.  Secondary lymphedema occurs from damage and overload of the lymphatic system.  It is a concomitant symptom that sometimes occurs (20% to 30%) during later stages of CVD.  The occurrence is mostly likely much higher since secondary lymphedema is not always correctly identified and diagnosed.

As chronic venous disease (CVD) progresses to later stages, symptoms of lymphedema begin to emerge. These symptoms are referred to as secondary lymphedema or phlebolymphedema.

The article describes methods for the practitioner to use to distinguish between venous and lymphatic complications.

When a patient has leg swelling it is important to understand the origin of the swelling because it affects how the symptoms are treated.  The article gives the example of a patient who was diagnosed on clinical grounds as having primary lymphedema and was treated for several decades with compression, however the swelling in her legs did not subside (see Fig. 1 left below, ref article Fig 1.).  It was not until venography was done that it was realized that the complication was due to a stenosis in the iliac vein.  A stent was used to correct the stenosis.

The author highly recommends that the best way to diagnose the origin of a swollen leg is to use IVUS (intra-vascular ultrasound).  IVUS is a technique where a catheter with a transducer on the end is navigated through the venous vasculature and measures the ultrasound of the vein interior giving information about the venous perimeter, structure of the walls and whether there is a narrowing or occlusion.  IVUS is much like standard ultrasound in that it is an imaging technique.

The author makes an important point that IVUS is much preferred over venography when diagnosing the origin of swollen legs.  The reason is because venography can be misleading depending on the angle or viewpoint that the image is taken.  In venography contrast dye is injected into the vein and imaged.  As shown in Fig 3 below left (from ref article Fig 3) the vein looks normal.  However, the IVUS shown on the right indicates a stenosis.  The reason the venograph did not show the stenosis is because if the stenosis makes an ellipse and the image is taken along the long axis the vein will appear normal.

**The author strongly suggests that before diagnosing a patient as having primary lymphedema and referring patients for conservative therapy, IVUS should be routinely used to rule out the possibility of a venous complication.**

Calf Pump Dysfunction

The body has developed mechanisms to move blood from the lower leg back to the heart against gravity.  These mechanisms include 1) the calf muscle that squeezes the deep veins, pumping fluid upward, 2) valves in the veins that open to allow blood flow upward toward the heart and close to prevent reflux or blood flow downward and 3) respiratory function where deep breaths inward reduces venous pressure and promotes flow upward.

Chronic vein disease (CVD) results from a break-down or dysfunction of any one of these mechanisms.  Venous valve malfunction is often discussed.  However, what is often overlooked is that patients with CVD often have an inadequate calf pump.

Vascular Wall Shear Stress

Compression has been shown to alleviate symptoms of chronic venous insufficiency. However, the physiological mechanisms of how compression works on the vasculature is not fully understood.  It is held that vascular wall shear stress (WSS) plays a role in CVI prevention through compression.  

The article "Effects of elastic compression stockings on wall shear stress in deep and superficial veins of the calf" by S.P. Downie et al reviews priciples related to vascular WSS, compression and its role in CVI prevention.

http://ajpheart.physiology.org/content/ajpheart/294/5/H2112.full.pdf


As fluid flows through a tube, stresses develop.  Shear stress components have the greatest impact on the fluid/tube interface.  Similarly, wall shear stress (WSS) due to blood flow has the greatest effect on the outer endothelial layers of the lumen.  An excellent reference describing WSS and blood flow through the vasculature is the article by T.G. Papaioannou et al, "Vascular Wall Shear Stress: Basic Principles and Methods".  

http://www.hellenicjcardiol.org/archive/full_text/2005/1/2005_1_9.pdf