Basic Pre-Quiz, how did you do?

The Basic Pre-Quiz was 20 questions for prospective students to identify areas of study in preparation to attend the Dr Vodder Basic Course (now called Level 1).

The quiz was completed 512 times with a median pass rate of 65%.

Which is a good score (top score 100%, mean 61% ± 26%), and close to the pass mark required for the course (70%). There was an 89% completion rate and most people finished in under 8 minutes. What's more interesting though, is which answers did most people know? And which concepts were least understood?

The most correctly answered questions were the true/false options on the effects of MLD.
  1. True, MLD helps to remove circulating proteins from the tissues (91%).

  2. True, MLD initiates mechano-receptor mediated pain relief (85%).

Least understood were the intrinsic mechanisms of lymph-motoricity, and the effect of MLD on lymphatic pumping (<50%). Both are complex concepts, not helped by a good deal of misinformation available in the public realm. The most misunderstood questions in the original quiz are addressed below.

But if you want to jump straight into the revised quiz you'll find it here.
Thank you to everyone that contributed to the Basic Pre-Quiz

Most mis-understood concepts

Q: Which lymph vessels are NOT formed of lymphangions?

The correct answer is the initial lymph plexus, but only 40% got this correct, with thoracic duct incorrectly selected almost as often (38%). Other options were pre-collector (13%) and lymph collector (2%).

The thoracic duct, although the largest lymph vessel in the body and easily seen with the naked eye, is made of contiguous lymphangions (the portion of a vessel between two internal valves). These 'tiny hearts' are the functional unit of the collector vessels, and responsible for transporting the lymph and preventing lymph status. Initial lymph vessels have no internal valves and are not lymphangions.

The initial lymph plexus is a capillary like network specialised for lymph formation at the tissue / vessel interface.

Lymph is formed at the initial lymph vessels by uptake of the lymph-obligatory-loaded from the extra-cellular spaces. The formed lymph passes into pre-collector vessels which are the first lymphangions in the lymph pathway. End to end lymphangions form the rest of the lymph vessel system, including the thoracic duct. Read more about vessels and valves in the #TalkingLymph post on lymph flow here.

Q: Which of the following is an intrinsic mechanism of lymphatic pumping?

The only intrinsic mechanism among the options was the automyogenic property of lymphatic smooth muscle which was correctly selected only 49% of the time.

But I can see why people also selected

  • skeletal muscle contractions (25%)

  • MLD (15%)

  • intestinal peristalsis (11%)

All are factors which increase lymph flow, but although MLD does influence lymph pumping, it is an extrinsic mechanism. Skeletal muscle movements and intestinal peristalsis support lymph flow by varying external pressure to the lymph vessels, another extrinsic factor. Read more about lymphmotoricity in the #TalkingLymph post here.

Q: Does MLD increases lymphatic pumping by increasing tissue pressure?

This is a bit of a trick question because intuitively the answer is yes, MLD does increase lymphatic pumping. By applying specific stretch and shear forces on the lymph collectors MLD stimulates neural reflexes that initiate contraction of lymphatic smooth muscle. Read more in the #TalkingLymph post on MLD here. But the answers to this question in the quiz were split down the middle (true 50.4%, false 49.6%) and the problem is the second part of the question - by increasing tissue pressure. Again this appears correct because MLD does increases tissue pressure slightly which influences lymph formation at the initial lymph plexus, but increasing tissue pressure itself does not directly influence contraction of the lymph vessels. It is a subtle, and some might say pedantic point, and maybe a little ambiguous for a simple true false answer format. It is not in the revised quiz.

Q: What is a dynamic oedema?

Q: Does MLD increase filtration at the blood capillary?

These two questions were both high on the list of misunderstandings, with only just over 50% correctly answering that a dynamic oedema is a problem of excess capillary filtrate, and over 45% incorrectly stating that MLD increases the capillary filtrate. So let's review capillary filtrate.

The four main forces are;

  • hydro-static blood pressure (drives filtration)

  • hydro-static tissue pressure (opposes filtration)

  • oncotic blood pressure - blood protein level (opposes filtration, drives resorption)

  • onctoic tissue pressure - tissue protein level (supports filtration)

We can apply these forces to a model where the capillary is like a tap into the bath in which all body cells live. Nutrient rich fluid is delivered continuously from the capillary and the 'used' fluid is removed continuously by the action of the drain, ie the lymph system. Hydro-static blood pressure and oncotic tissue pressure are the forces that increase flow at the tap. They are opposed by blood oncotic pressure and hydro-static tissue pressure which are the forces that turn down the tap.

A pure dynamic oedema is a problem with the tap alone, the lymph system is probably working maximally, but the volume of fluid leaving the capillary is overwhelming, eg during congestive heart failure. If the problem is purely with the drain the term lymphoedema is used, but most people affected by oedema have multiple contributing factors and the term chronic oedema is a more useful term clinically.

To go back to the question Does MLD increase filtration at the blood capillary? It is well known that MLD increases lymphatic pumping but almost half of the quiz respondents thought it also increased the total capillary filtrate.

In fact MLD reduces filtration at the blood capillary in 3 ways.
  1. Small increase in hydro-static tissue pressure - MLD applies 20 - 40 mmHg pressure into the skin and underlying tissue

  2. Decreased oncotic tissue pressure - Increased lymphatic pumping removes tissue proteins

  3. Pre-capillary sphincter dilatation - increases blood velocity through the capillary (12%) but does not increase hydro-static blood pressure

The action at the pre-capillary sphincter is via sympathetic neural reflexes and you can read more about this in the #TalkingLymph post on the effects of MLD and stress here.

Differences at the capillary explain why MLD is indicated for chronic oedemas and pressure massage is not.

What about pressure massage? Pressure massage is usually aimed at deeper structures such as fascia, skeletal muscles and joints, and applies compressive forces to the skin and subcutaneous compartment. These forces are much higher than those used in MLD and could be well over 100mmHg and this may force excess fluid from the capillary.

Friction and repetitive pressure movements increase local blood flow which increases hydro-static capillary pressure. If the connective tissue bath belongs to someone with a functioning lymph system the increased lymph load up-regulates lymphmotoricity and the bath gets a lovely flush through. Read more about lymphmotoricity here.

If the bath belongs to someone with a compromised lymph system, any increase in capillary filtrate is a risk factor for triggering overt lymphoedema or exacerbating existing symptoms and is a relative contradiction to pressure massage.

To find a health professional trained in lymphoedema management