Venous foot pump

[Gerrard Farrell]

I read somewhere that the venous foot pump can be viewed as priming the calf pump in a fashion that resembles the atria priming the ventricles .

With regard to how the foot pump functions , the idea that the vessels of the plantar venous plexus are stretched during weight bearing , and that this stretching empties them , still persists . I believe that this idea is demonstrably wrong .

An article published in 2012 ,E Lindsay et al ,(see below ) lays out the argument for a vessel stretch mechanism very well .

Here are 2 quotes from the article -

1 When weight is applied to the sole of the foot, the plantar arch is flattened. The resulting longitudinal stretching of the veins allows the blood to be pumped along the long and short saphenous veins into the deep calf veins, even when the patient is in the upright position.

2 Gardner and Fox also found that ‘weight bearing on a flaccid hemiplegic leg with the knee locked also caused flow in the femoral vein’, indicating that the foot pump may be functional in paraplegic legs. It has also been suggested that stretching the arch without weight bearing may be sufficient to empty the veins (Gardner and Fox, 1983).

The problem with the stretch to empty theory is that veins are viscoelastic and stretching them will not effectively empty them .

Here is a simple experiment that is even cheaper than my previous HP sauce efforts .
I filled a simple latex glove with cold water . Then I got someone to hold the fingers whilst I pulled up on the open end of said glove to stretch it . Far from the glove emptying ,more room was created for addition water .

I was pretty certain of what would happen before I started but thought I would check anyway .

Any thoughts ?


Short-stretch compression bandages and the foot pump - Nursing Times

https://www.nursingtimes.net/.../030624Short-stretch-compression-bandages-and-the-f...




by E Lindsay - Cited by 2 - Related articles
9 Nov 2012 - leg, focusing on calf-muscle function and the action of the foot pump. They discovered that the plantar venous plexus fills when the foot is ..

[Dan Robbins]

Re: Venous foot pump

Hi Gerrard,

One of the major issues with the sauce and glove experiments you describe is the lack of valves. In human leg the valves prevent the pooling (which is the effect you are seeing in the open glove). A second issue is that the open glove and judging by the mess you described from the sauce bottle, fluids were not in a sealed/closed system. Without a closed system fluids will not be affected by Boyle's law and Bernoulli's principle. It is also worth noting that Unlike water, blood is non-Newtonian as its viscosity increases at low flow velocities - this could mean that rate of the various muscles pump actions and/or the heart beat could change the influence on blood flow (from muscle pumps or forces).

I am not an expert in vascular biomechanics and only have limited knowledge of the foot, calf and respiratory pumps; therefore I cannot offer direct answers/solutions. I would suggest that you would get better results if you designed an experiment on blood flow in humans. If you use something like Laser Doppler or ultrasound imaging you could assess foot and'or calf pump influences on leg blood flow in a seated position without too much hassle. You could potentially extend this to movements such as squatting for comparison. If you have access to more advanced (expensive) equipment, you may be able to assess walking/running.

Regards
Dan

[Gerrard Farrell]

Re: Venous foot pump

Hi Dan
Taking the second part of your reply first , I have to say I agree that more advanced studies into certain aspects of venous return ( centrifugal effects ) in the lower limb are required than can be provided by a bottle of sauce .

With regard to the glove experiment as a means of demonstrating that stretching out veins does not make for an effective pump , I feel something that simple is really all that is required .

But let's say you take a length of vein , valves and all ,fill it with blood and tie off the bottom end . Now hold the vein upright and stretch .Yes the circumference will decrease but the length will increase giving little change in volume and a very ineffective pump .
You mentioned Bernoulli's principle ,above , but that is about the conservation of energy whilst the foot pump is all about generating energy .

The main people in the foot pump story are AMN Garder and RH Fox ( although many others have played a role before and since ) . They wrote " We have discovered a venous pump mechanism in the sole of the human foot that is able to return blood from the leg up into the abdomen with no assistance from muscular action " . And to a certain extent they had . It just that ,in my opinion , they misunderstood the mechanism by which their pump worked .

They carried out a series of experiment including introducing a contrast medium into the deep plantar veins . Toe flexing did not move the contrast medium out of the veins but weight bearing did so the pump does not work by muscular contraction alone .

How does this powerful pump work ?
In my opinion ,during weight bearing , the bony arch of the foot lowers and the plantar fascia , which is continuous between medial and lateral aspects of the foot ,is stretched . The muscles between the two elements are subject to a volume which is trying to reduce ,and this results in increased intermuscluar pressure .

This powers the foot pump . No muscle to compress means a far less effective pump . Muscle with some tone will produce a more effective pump etc

Gerry

[Gerrard Farrell]

Re: Venous foot pump

A very interesting paper was just published by the Karl Zelik lab on soft tissue work during early gait (see below ) . Such soft tissue work would include the deformation of the heel pad and compression / distortion of the other tissues of the foot .

It seems to me that the compression of the tissues that lie between the bony arch of the foot and the plantar fascia would also play a large role in the soft tissue work done by the foot .
If that is indeed the case then one might expect to see a lower contribution from this source when walking uphill but a higher , and later contribution when walking downhill (foot slapping action ) .

I would be very interested to hear what Karl and Eric think of the above .

Gerry

Paper Foot and shoe responsible for majority of soft tissue work in early ...

https://www.ncbi.nlm.nih.gov/pubmed/30769210

by EC Honert - 2019
12 Feb 2019 - Foot and shoe responsible for majority of soft tissue work in early stance of walking. Honert EC(1), Zelik KE(2). Author information: (1)Dept. of ...

[Gerrard Farrell]

Re: Venous foot pump

Anyone who might have read my last few posts will be aware that my experimental equipment consists of a half empty bottle of HP sauce and a water filled surgical glove . This is more of the same !

The post above mentions a paper , very recently published by Hornet and Zelik , which looks at soft tissue work in the early stance of walking .

The post also raises the question of whether the tissues between the bony arch of the foot and the plantar fascia are compressed during gait and so contribute to soft tissue work .

So let's take the surgical glove, adapt it ,and use it to demonstrate tissue compression between the bony arch and the foot .

Take the glove ,empty it of water and tie off the fingers . Now turn it inside out and fill it again with water . Now tie off the top of the glove so that you have a small water filled sphere .
Next , place your cupped hand ,palm down , on a table . The lateral border of the hand lies flat on the table but the medial aspect will form an arch analogous to the medial arch of the foot .

Now place the water filled sphere under the arch /cupped hand , then press down to represent the lowering of the bony arch of the foot during weight acceptance during gait . You will notice that the sphere is compressed between the hand and the table (analogous to the plantar fascia ) and so it bulges inwards . Now place your free hand so that it stops the water filled sphere from bulging inwards ( this hand represents the medial part of the plantar fascia ) .You can appreciate how the water trapped in the glove is now pressurized as the cupped hand is pressed down .

Note ; in the case of the foot this system will not prevent the foot from pronating as the bony arch and the fascia will lower towards the ground as part of the same unit . Instead the intrinsics will act as
(1) a pressurized core reducing shear forces between the components of the bony arch
(2) an energy sump (soft tissue work )
(3) a pump for moving blood out of the plantar venous plexus


The intrinsic can of course do all of the above whilst at the same time acting to shorten the foot or reduce pronation , if they contract with sufficient force . The mechanism by which these muscles can contract whilst under transverse pressure is explained in this thread .(below )

Any thoughts ?

Hydraulically discrete fascicles in skeletal muscle [Archive ...


https://biomch-l.isbweb.org/archive/...p/t-28655.html



13 Feb 2016 - 2 posts - 1 author
If the perimysium is sufficiently impermeable then might it be possible that each fascicle is able to function as a hydraulically discrete unit with ...

[Gerrard Farrell]

Re: Venous foot pump

The WHOLE FOOT is a pump ! ( almost )

After a lot of reading on the subject it is starting to look to me like almost the entire foot is an "osseofascial pump " dependent for its power on the changing shape of the osseous components of the foot during weight acceptance .

As weight is accepted onto the reference foot during gait , the medial and lateral longitudinal arches and the transverse arch are compressed , leading to increased tension in the interconnected deep and superficial fascial structures that envelop the foot . This increase in tension causes compression of the soft tissues of the foot including most of the venous system , dorsal and plantar .

Fox and Gardner produce interesting before and after pictures of the coupled drainage of the dorsal and deep plantar venous components of the foot , see below. ( Note the almost total expulsion of blood from the venous components of the foot between the weight bearing and none weight bearing conditions) . The fascially related , coupled drainage of the plantar and dorsal aspects of the foot mean that perforator veins need not have valves .

On the plantar aspect of the foot ,when the bony arch of the foot is compressed and the fascia stretched ,the muscular tissues between the two are compressed and this force is transmitted to the plantar veins causing them to empty . However , Fox and Gardner found that the plantar foot pump (in my opinion one part of a greater whole ) could operate in less effective fashion in the paraplegic foot , presumably because the fatty infiltrate that replaces much of the plantar intrinsic musculature in such feet is a less effective transmitter of force . But it did still function .


The pressure generated by the foot , an osseofascial pump , increases with increased ground reaction forces allowing venous return from the foot to be maintained as centrifugal effects increase .

The venous pump of the human foot--preliminary report. - NCBI

https://www.ncbi.nlm.nih.gov/pubmed/6616290

by AM Gardner - 1983 - Cited by 169 - Related articlesBristol Med Chir J. 1983 Jul;98(367):109-12. The venous pump of the human foot--preliminaryreport. Gardner AM, Fox RH. PMCID: PMC5077034.

[Gerrard Farrell]

Re: Venous foot pump

Following some feedback ,the mechanism by which the whole foot becomes an osseofascial pump is not immediately apparent from the explanation I have given above , so this post is a bit of further explanation .

Quote from above -

"As weight is accepted onto the reference foot during gait , the medial and lateral longitudinal arches and the transverse arch are compressed , leading to increased tension in the interconnected deep and superficial fascial structures that envelop the foot . This increase in tension causes compression of the soft tissues of the foot including most of the venous system , dorsal and plantar ."

A way of understanding this is as follows .

Cup your hand as if you were trying to carry a little water in it or as if you were trying to cover a small egg on a table with your hand without crushing the egg . Maintain that hand shape as a friend puts a paper bag over the hand ,tightens the bag a litle to take up any slack and then tapes it in place with a few short pieces .

So now you have something very roughly analagous to an arched foot enveloped in fascia . Now place your hand flat on a table top and push down on top of it with your other hand . As the hand (foot) flattens the paper bag becomes tensioned . The bag represents both the deep fascia and the superficial fascias of the foot

In the foot the plantar fascia on the plantar aspect of the foot is continous with the fascia dorsals pedis . The superficial fascia is also continous going from plantar to dorsal .

[Gerrard Farrell]

Re: Venous foot pump

TYING THE FOOT PUMP TO THE CENTRIFUGAL EFFECT .

So for calculating angular acceleration (ac) we have ac = v x v/r This means that if an individual has a leg length of 0.7 m and is walking at 1.5 m/s then the angular acceleration is 3.2 m/s . Thus for the stance leg during gait the force acting on the column of blood at the ankle is not just gravity x mass , as has previously been the assumption but gravity plus angular acceleration giving a total force of about 13.2 x mass .

Now , after toe off , the reference foot undergoes rapid acceleration , quickly reaching a velocity which allows it to catch and pass the body , so that it is in place for the next cycle . So let's say the reference foot reaches 3 m/s during the swing phase , so that gives an angular acceleration of (3x3) /.7 = 12.8m/s/s
So the force applied to the venous valves at the ankle by the section of the column of blood immediately above is the mass of the blood x 22.8 ,not mass x 10

That's a big difference compared to what was originally thought .

What about running at say 3m/s ? During the swing phase that would give a foot velocity of about 6m/s . So angular acceleration = vxv/.7 = 51 m/s/s

So for our section of the column of blood , that gives a force on the valves of mass x 60 . Not mass x ten (gravity only ).

So with regard to venous return during gait , when you add the centrifugal effect into the equation ,in addition to gravity , you can see how vital the foot and calf pumps are .






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