What happens to the venous foot pump in diabetes ?

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The venous foot pump plays a crucial role in moving blood from the foot back towards the heart, both against gravity and against the centrifugal effect generated by walking/running.

A number of studies have looked at this mechanism and, in bed bound patients, hospitals employ inflatable devices placed around the foot to take advantage of it to reduce the risk of deep vein thrombosis.

The exact mechanism by which the venous foot pump works is the subject of some debate but it is clear it is greatly dependent on compression of the veins of the plexus between the intrinsic foot muscles, not veins stretching as the foot lengthens during weight acceptance.

It is known that circulation is often compromise in the feet of diabetic patients and that the intrinsic foot musculature often begins to atrophy even before the signs of neuropathy appear. But what does this mean for the venous foot pump? As far as I can tell, nobody has ever looked !

If medical devices exist to activate the pump in hospital patients, why is it being ignored in diabetes patients?

 

The position of the large veins that make up the plantar venous plexus means that they are not compressed directly by ground reaction forces but that moving blood out of these veins is reliant on pressure being generated in the muscles that surround them.

An idea of what would happen to the plantar foot pump in diabetic neuropathy can be gained by looking at other conditions which result in muscle atrophy, for example the feet of paraplegic patients. Blood is still pumped out of the feet of paraplegic patients via the plantar pump when they bear weight on their feet, but flow is poor and erratic.

Can atrophy of the intrinsic foot muscles be prevented in the diabetic patient? Yes, would appear to be the answer, provided resistance exercises with sufficient stimulus are used ( Hohne et al ) . Indeed ,even in patients with neuropathy, muscle growth can be encouraged.

In diabetes, muscle wasting is not caused merely by damage to the nervous system, but also by interference with muscle metabolism itself, and resistance exercises can help combat this.

Here is part of a recent paper summarizing the problems that diabetes causes in skeletal muscle.
The Vicious Cycle of Type 2 Diabetes Mellitus and Skeletal Muscle Atrophy: Clinical, Biochemical, and Nutritional Bases

Jose M Lopez-Pedrosa 1, Maria Camprubi-Robles 1, German Guzman-Rolo 2, Andres Lopez-Gonzalez 1, Jose Manuel Garcia-Almeida 3, Alejandro Sanz-Paris 4, Ricardo Rueda 1
Affiliations Expand

• PMID: 38202001
  
• PMCID: PMC10780454
  
• DOI: 10.3390/nu16010172

Abstract

Today, type 2 diabetes mellitus (T2DM) and skeletal muscle atrophy (SMA) have become increasingly common occurrences. Whether the onset of T2DM increases the risk of SMA or vice versa has long been under investigation. Both conditions are associated with negative changes in skeletal muscle health, which can, in turn, lead to impaired physical function, a lowered quality of life, and an increased risk of mortality. Poor nutrition can exacerbate both T2DM and SMA. T2DM and SMA are linked by a vicious cycle of events that reinforce and worsen each other. Muscle insulin resistance appears to be the pathophysiological link between T2DM and SMA. To explore this association, our review (i) compiles evidence on the clinical association between T2DM and SMA, (ii) reviews mechanisms underlying biochemical changes in the muscles of people with or at risk of T2DM and SMA, and (iii) examines how nutritional therapy and increased physical activity as muscle-targeted treatments benefit this population. Based on the evidence, we conclude that effective treatment of patients with T2DM-SMA depends on the restoration and maintenance of muscle mass. We thus propose that regular intake of key functional nutrients, along with guidance for physical activity, can help maintain euglycemia and improve muscle status in all patients with T2DM and SMA.

 

Atrophy of the intrinsic foot muscles is just about the 1st change that happens in the feet of affected diabetics, occurring before vascular disease and signs of neuropathy. It seems probable that muscle atrophy will then lead to poorer function of the venous foot pump ( as with the feet of paraplegic patients), reduced circulation, and associated pathologies.

And yet it may not need to be like that.

Research has shown that the toe flexor muscles( including the intrinsic foot muscles) of neuropathic feet in diabetic subjects respond greatly and quickly to targeted exercise with gains of 55% in toe flexor strength in just 8 weeks. ( Angela Hohne 2012)

The key is sufficient stimulus .

Check out the set up used by Hohne and her colleagues included below ( the same set up was used in further research by Goldmann 2013) .

The set up produced not just great strength gains but also promoted muscle growth. ( 5% growth in intrinsic muscle mass in 8 weeks)

 

What causes foot muscle atrophy in diabetes ?

Many older texts seem to suggest that motor nerve damage reduces activity in these muscles and hence causes atrophy . This is not a surprising conclusion since atrophy and neuropathy often come hand in hand. However, we also know that muscle wasting often precedes neuropathy in the feet of diabetics.

Might muscle atrophy damage the venous foot pump, already identified as extremely important, causing poorer circulation in the foot, which then contributes to neuropathy?

Consider, veins running through layers of muscle in a contractile state will be subject to greater compression than veins running through a mass of fatty infiltrate and thus emptied much more efficiently.

So we have muscle atrophy causing neuropathy/nerve damage.

 

Elsewhere on podiatry arena, I put forward the idea that the entire foot is an osseofascial pump with blood being moved out of the plantar venous plexus, and lateral and medial dorsal veins, simultaneously . This might give of volume of blood being forcibly pushed into the superficial and deep venous return systems of 45ml+ ( left ventricular output in a male at rest is 75ml )

For the system to be effective, blood must be forced out of both plantar and dorsal veins simultaneously since they are connected by valveless plantar veins ( see diagram 1 from Uhl 5 ,6,7,8)

Check out the linked to video of an inflating foot pump and look at the ultrasound image, top left ( about 15 seconds into the video ) . Note that as the pump inflates on the plantar aspect, the securing straps on the dorsal aspect tighten, compressing the plantar veins and moving blood from them into the saphenous veins. You can see these veins empty with repeated compressions.

During gait, changes in foot shape likely tension the fascia surrounding the foot, something that is mimicked by the artificial pump straps . The mechanism is explained in the bottom video .





https://youtube.com/shorts/G29GmQ9tV2w?si=NbLKm_c1JOvjAcRt

 

The Vadoplex video linked to above shows the device moving blood not just out of the plantar venous plexus but also the veins on the dorsum of the foot. This action is similar in some regards to the way blood seems to be moved out of the dorsal veins during normal gait .

Below is an illustration from a paper by Fox and Gardner showing blood in the veins of the foot before and after weight bearing . Note that blood is moved out of the plantar and dorsal veins . Blood is being moved out of the dorsal veins almost completely, it is not merely passing from the deep plantar veins into the dorsal veins via communicating veins.

Both plantar and dorsal vessels are subject to compression during weight bearing or they would not empty as completely as they do.

Intrinsic foot muscle atrophy, with subsequent fatty infiltration, will likely affect both the plantar venous plexus and the dorsal system, since pressure needs to be created in both systems simultaneously for optimal function.

Movement of blood out of the dorsal veins during weight bearing seems never to have been properly studied, at least in connection to a compression mechanism . Indeed, before I raised the idea 5-6 years ago, it seems never to have been considered.

Intrinsic muscle loss in diabetes is modifiable but the effects of the development of a diabetic foot on the plantar venous appears never to have been studied !



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Imagine you are standing holding a bucket full of water . If you lift the bucket above your head, inverting the bucket as you do so, the water will pour out over your head. But now imagine you hold the bucket and windmill your arm quickly around in the sagittal plane . The water stays in the bucket due to the centrifugal effect.

During gait, as our legs move backwards and forwards relative to the rest of the body ,the centrifugal effect creates a force that resists blood being returned to the heart from the lower limbs. Since the foot is the most distal part of the lower limb it moves at the greatest relative speed and veinous return is resisted the most .

Venous return during gait is not just against gravity but also considerable centrifugal forces. That is one of the reasons why a properly functioning venous foot pump is so important.

This seems never to have been considered at all in the literature, until the discussion linked to below between myself and Professor Ton van den Bogart, over on the Biomch-l site. - Centripedal forces and the calf muscle pump - Biomch-L

"Let's try to put some numbers on this effect.

The centrifugal effect would be largest during sprinting, where the swing time is about 1/3 s and the leg may swing through a 90 degree arc [1]. That corresponds to an angular velocity of 270 degrees/s or 4.5 radians/s.

The radius of the arc is probably 0.7 m or so. This gives you a centrifugal effect of 4.5^2 * 0.7 = 14 m/s^2.

This seems significant, more than doubling the effect of normal gravity. " Professor Bogart

I have discussed these topics before on Podiatry Arena, so why start a new thread ? Well, because I believe the plantar venous foot pump, or more accurately the osseofascial foot pump to include the active dorsal aspect, is very important and, especially with regard to the diabetic foot, greatly understudied, and no movement seems to have happened since the topic was last raised.

What happens to the effectiveness of the foot pump in the feet of diabetics? IMO, this question needs answered. If blood flow out of the foot is being negatively affected then does this negatively affect blood flow into the foot and tissue perfusion overall, perhaps leading to disastrous outcomes.