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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[Gerrard Farrell]

Returning to this thread and "the whole foot is a pump", well so what ? Well, venous return via the skeletal muscle pump is a crucial part of the cardiovascular system, especially when standing or during gait .Reduced venous return can lead to postural hypotension when moving from seated to standing and this may result in falls .



I asked myself the following question : Since older individuals are more likely to have heart function problems, and also lower limb muscle loss caused by sarcopenia, can rebuilding the musculature of the lower limb, and of the foot in particular, assist with cardiac function and improve general health in this group?

If you like mechanics you might enjoy this series of posts I recently placed on Podiatry Arena on this topic .

1. Increased venous return to right side of heart results in greater stroke volume from left ventricle and so flow of blood around body.
   
   Starling mechanism involves atria contracting and preloading ventricles> stretching the cardiac muscle before ventricular contraction.
   
   Venous return reduced if lower limb muscle lost to aging but this can be reversed by progressive resistance exercise . Muscles in foot play key role in venous foot pump but are amongst most affected by aging.
   So if venous return from the lower limb is reduced in the elderly because of skeletal muscle loss, can restoring skeletal muscle restore better venous return ? Can't seem to find much on this topic .
   
   Also ,to avoid confusion the sentence "Venous return reduced if lower limb muscle lost to aging but this can be reversed by progressive resistance exercise" in post Forum would be better written "as venous return from the lower limb may be reduced if muscle is lost due to aging, but muscle loss due to aging can often be reversed by progressive resistance exercise" .
   
   It needs to be remembered that venous return from the lower limb is likely not just about overcoming gravity but also a significant centrifugal effect produced during gait.
   
   I am not an expert in this area of physiology but find it to be of great interest.
   
   
   
   Post 2
   
   
   eISSN 2765-5628
   pISSN 1598-6756

   • New Treatment of Varicose Veins through Muscle Regeneration of Lower Leg Muscles (Especially Calf Muscle) Without Removal of Varicose Veins
     
     Ki Ji Lee, M.D., Ph.D.
     Author Affiliations
     Correspondence to : Ki Ji Lee, 15 Saemal-ro, Guro-gu, Seoul 47848, Korea, Deparment of Pediatrics, Woorisoa Seoul Hospital
     Tel: 02-858-0100, Fax: 02-856-0032
     E-mail: leekiji@naver.com
     Abstract
     
     Go to
     The calf muscle pump is the motive force enhancing venous blood return from the lower extremity to the heart. It causes displacement of venous blood in both vertical and horizontal directions, generates ambulatory pressure gradient between the thigh and lower leg veins, and bidirectional streaming within calf perforators. Ambulatory pressure gradient triggers venous reflux in incompetent veins, inducing ambulatory venous hypertension in the lower leg and foot. Bidirectional flow in calf perforators enables quick pressure equalization between deep and superficial veins of the lower leg; the outward (into the superficial veins) oriented component of the bidirectional flow taking place during calf muscle contraction is not a pathological reflux but a physiological centripetal flow streaming via the great saphenous vein into the femoral vein. Calf perforators are communicating channels between both systems, making them conjoined vessels; they are not involved in generating pathological hemodynamic situations and do not cause ambulatory venous hypertension. Pressure gradient arising during calf pump activity between the femoral vein and the saphenous remnant after abolishing saphenous reflux triggers biophysical and biochemical events, which might induce recurrence. Thus, abolishing saphenous reflux removes the hemodynamic disturbance but simultaneously generates a precondition for reflux recurrence and the return of the previous pathological situation; this chain of events has been termed the hemodynamic paradox. But this review showed that varicose veins could be improved quickly through lower leg muscles (especially calf muscle) regeneration by increasing mitochondrial cellular energy (adenosine triphosphate) of leg muscles without removing varicose veins.

   Which group of clinicians should be looking after calf and foot musculature in older adults ?
   
   
   
   Post 3
   The plantar venous plexus is located on the plantar surface of the foot and is made up of large diameter veins . During gait these vessels fill with blood which is then expelled back towards the heart with high force during weight acceptance. A typical volume of blood is estimated as being between 20-35ml of blood. It is worth noting that this pump operates just as well in the cavus foot as the planus foot, but more of that later.
   
   It has been suggested that the foot pump acts as a primer for the calf pump and even that it contributes just as much to venous return as the calf pump itself. The musculature in the thigh also contributes to venous return.
   
   The following may not be backed up by the literature and can best be described as my opinion based on what I have read.
   
   Venous return from the lower limbs, powered by skeletal muscle function, has a huge role to play in cardiovascular function.
   
   The human heart has four chambers 2 atria and 2 ventricles . The atria have a number of functions one of which is to contract and fill the ventricles with blood just before these contract sending blood to the lungs ( right ventricle) and oxygenated blood to the rest of the body ( left ventricle) .
   
   Taking the left side of the heart ; when the atrium contracts it fills the left ventricle and this filling action stretches the muscles of the ventricle (preloading ) which then contacts ejecting more blood than it would if the muscle had not been pre-stretched.
   
   This is speculative ; The heart may beat /contract via active and passive mechanisms. The active component involves the ATP/ oxygen burning, contractile components of the cardiac muscle and the passive component is reliant on the elastic tissues in the cardiac muscle mass being stretched and thenrecoiling. This stretch/ recoil mechanism requires little oxygen ( blood via coronary arteries) and is powered largely by atrial activity and the pressures generated during venous return via the skeletal activity.
   
   As physical activity becomes more demanding so the proportion of blood pumped by active contraction of the ventricles verses passive contraction will change in favour of passive elastic recoil doing more of the work . Therefore, as higher cardiac output is required so venous return becomes more important.
   
   Perhaps the hearts of older people, with reduced calf, foot, thigh musculature, might struggle to utilize the "free" pumping action of the which depends on venous return.
   
   Oxygen cheap and expensive ventricular activity ? Simultaneous sure, but which may be thought of as distinct components.
   
   
   
   Post 4
   
   Bringing this back round to the foot, it's pretty clear that the pumping mechanism in the foot engaged during weight acceptance, the venous foot pump, has an important role to play in venous return and therefore, in my opinion, in cardiac function during gait /standing.
   
   So what? Well , the venous foot pump needs a healthy intrinsic musculature to function properly . Blood is still pumped out of the feet of paraplegic patients when they bear weight on their feet, but flow is poor and erratic.
   
   The muscle function in the calf and foot can be improved in the elderly with progressive resistance exercise and therefore circulatory problems linked to sarcopenia could be regarded as a modifiable risk.
   
   Foot calf strengthening will likely improve venous return, cardiac function, and possibly postural hypotension. Postural hypotension can lead to falls, especially in the first 60 seconds or so after standing from a seated position.
   
   
   Post 5
   "Surprisingly, the single best predictor of a senior citizen falling is toe strength. In a prospective study of 300 older adults, Mickle et al. (3) discovered that non-falling seniors had 20% more toe strength than the seniors who fell. Interestingly, there was no difference in quadriceps or ankle strength between the fallers and the non- fallers, confirming that toe weakness, not generalized weakness, is responsible for the falls. Unfortunately, toe weakness is extremely common in senior citizens: compared to their younger peers, older adults have toe strength declines of more than 35%, which greatly increases the risk of falling (4)."
   Tom Michaud
   
   Reduced toe strength may negatively impact a persons ability to maintain balance and avoid falling through a mechanical mechanism but I believe other factors need to be considered. Reduced toe flexor strength may mean reduced intrinsic muscle mass and a poorly functioning foot pump . This in turn might lead to postural hypotension when moving from seated to standing, increasing the risk of fainting or dizziness and a fall. Apparently, the connection between the skeletal muscle pump and falls is presently under investigation at Newcastle University, UK .
   
   A healthy foot pump can move a volume of between 20-35 ml of blood out of the foot with enough force to lift a column of blood all the way to the heart. 2 feet could equal as much as 70 ml of blood (the same as the volume of blood pumped from the left ventricle during a single beat body whilst at rest ).
   
   
   
   
   post 6

1. Ok, so let's assume, for now, that the plantar venous plexus has an important role to play in venous return and that this might make the mechanism important in cardiovascular mechanics, postural hypotension, and falls prevention.
2. 
   But how does the plantar venous pump work ?
   
   We can forget "necking down" as emptying a viscoelastic tube of fluid by stretching it is not possible in the context ,valves or no.
   
   The vessels of the plexus lie within the intrinsic muscle mass of the foot and so it's a pretty safe bet that what happens to the muscles during weight acceptance is what drive the pump. It could be muscle contraction or it could be muscle compression through weight bearing ,but either way muscle needs to be there . Replace muscle with a defuse fatty infiltrate and the pump will be diminished whether the mechanism is contraction , compression, or a combination of the two.
   
   As with diabetic feet, the feet of older people have less contractile muscle mass than healthy younger people.
   
   Both the feet of older people ( Mickle et al) and those of diabetics with neuropathy ( Hohne et al), can be strengthened by resistance exercise, indeed Hohne managed to increase intrinsic muscle mass as well as strength, employing an exercise regime of just 10 mins 3x a week ( as best I can remember !) .
   
   The venous foot pump is greatly diminished in the affected foot of hemiplegic patients but still exists as reduced erratic outflow . Exercise will not restore the intrinsic foot musculature of a hemiplegic patient but it can be restored in diabetics and older people . If it can be stored it can almost certainly be prevented in the first place.
   
   Falls can absolutely destroy the confidence of older people and cost health services a huge amount of money.
   
   
   
   

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[Gerrard Farrell]

Here are "before and after weightbearing" images of the foot from a paper by Fox and Gardner. Note that it is not just the plantar vessels that empty but the dorsal vessels as well . That's a lot of blood under high pressure being sent back towards the heart .

How do the dorsal veins empty on weightbearing ? Well, I believe post 7, above, answers this question;

"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 little to take up any slack and then tapes it in place with a few short pieces .

So now you have something very roughly analogous 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 continuous with the fascia dorsals pedis . The superficial fascia is also continuous going from plantar to dorsal ."

A video of a very simple model can be found via the link at the bottom of this post.







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https://youtube.com/shorts/G29GmQ9tV...CwAKQeV-e9SzoG Venous foot pump , dorsal aspect ,a theory 20210320 110916

www.youtube.com › shorts
dataurl626815.jpg

0:08

In my opinion, almost the entire foot can be viewed as an osseofascial pump .All aspects of the pump are activated during weight bearing ...
YouTube
"In my opinion, almost the entire foot can be viewed as an osseofascial pump .All aspects of the pump are activated during weight bearing with the plantar venous plexus being emptied through compression of vessels within the plantar muscle mass as change in foot shape is resisted by the fascias of the foot . The dorsal veins, such as the long and short saphenous veins , are emptied primarily by the fascia of the foot resisting change in foot shape in the transverse plane . In this simple video, cardboard represents the bony arch of the foot ,plastic wrapped around the cardboard and the blue glove finger represents the fascia of the foot, and a finger taken from a glove and filled with shaving cream, represents a blood filled vein on the dorsal aspect of the foot . Compression of the cardboard puts the foam filled glove under pressure causing it to empty . This is analogous to the system found in the foot where weight bearing empties the dorsal and plantar veins at the same time ."