Evidence-based physiotherapy and rehabilitation resources
Editorial & review policy
Evidence-based physiotherapy and rehabilitation resources
Editorial & review policyHuman Physiology · Cardiovascular system
The microcirculation is where blood finally does its job: exchanging fluid, nutrients and waste with the tissues. When that exchange goes wrong, tissues swell. This page explains how fluid moves, how lymphatics bring it home, and how physiotherapists assess and treat oedema and lymphoedema.
Part 3 · Cardiovascular System · Chapter 14 of 47
By the end of this page you should be able to:
Swelling is one of the commonest findings you will see: a sprained ankle, a post-operative knee, the legs of a patient with heart failure, or the arm of a woman treated for breast cancer.
Each swelling has a cause, and the cause decides the treatment. Elevation and movement help some swellings, compression helps others, and some swellings are a warning sign that needs medical review first.
The microcirculation is made up of arterioles, capillaries, venules and the lymphatic capillaries that lie among them. Arterioles control how much blood enters each capillary bed. Capillaries, a single layer of endothelial cells, are where exchange happens. Venules collect the blood again.
Figure 1 · The microcirculation
Not every capillary is open all the time. In resting muscle many are closed; during exercise, local metabolites relax arterioles and precapillary sphincters, so far more capillaries open. This shortens the distance oxygen must diffuse and greatly increases the surface for exchange.
Figure 2 · Three types of capillary
| Type | Where | Wall | What passes easily |
|---|---|---|---|
| Continuous | Muscle, skin, lung, brain | Unbroken, with narrow clefts | Water and small solutes |
| Fenestrated | Kidney glomerulus, gut, endocrine glands | Small pores in the cells | Large amounts of fluid |
| Sinusoidal | Liver, spleen, bone marrow | Wide gaps, incomplete basement membrane | Proteins and even cells |
In the brain, continuous capillaries with very tight junctions form the blood–brain barrier, which protects neurons from many substances in the blood.
Chapter 4 introduced the Starling forces: capillary pressure pushes fluid out, and the protein (oncotic) pressure of plasma holds it in. The traditional picture had fluid filtered at the arterial end and reabsorbed at the venous end.
Levick and Michel reviewed the modern evidence. In most tissues, absorption is only transient; at steady state, slight filtration continues along the whole capillary, even in venules [1]. The excess is returned by the lymphatics.
The key change is the endothelial glycocalyx, a thin gel of sugar-protein chains lining the inside of the capillary. It is now recognised as the true semipermeable layer [1]. The protein concentration that matters is the one just beneath the glycocalyx, not the one in the wider tissue [1, 2].
Exam answer versus modern view
For the exam, draw the classic Starling balance and then add one paragraph on the revised view. The oncotic gradient opposes filtration but does not reverse it, and filtered fluid returns as lymph [2].
One practical consequence is that drips of protein solution cannot be relied on to pull oedema fluid back into the blood [2]. Another is that the lymphatics are not a minor overflow; they are the main route home for tissue fluid.
Lymphatic capillaries begin as blind-ended tubes in the tissues. Their endothelial cells overlap like loose roof tiles and are tethered to the surrounding tissue by anchoring filaments. When tissue fluid increases, the filaments pull the flaps open and fluid enters.
Figure 3 · How lymph moves
Lymph then flows into collecting vessels divided by valves into short segments called lymphangions. Each segment contracts rhythmically, pushing lymph forward past the next valve. Skeletal muscle contraction, breathing and the pulsation of nearby arteries add external pumping.
Lymph passes through lymph nodes, where immune cells sample it, and finally drains into the great veins at the root of the neck. A few litres of lymph return to the blood each day.
| Lymph pump | How it works | What you can use clinically |
|---|---|---|
| Intrinsic | Smooth muscle in lymphangion walls contracts in sequence | Warmth and gentle stretch may help; little direct control |
| Skeletal muscle | Contracting muscles squeeze collecting vessels | Active exercise, especially rhythmic |
| Respiratory | Breathing changes chest pressure, drawing lymph centrally | Deep breathing exercises |
| External compression | Bandages or garments limit filtration and support pumping | Compression therapy |
Oedema is an excess of fluid in the interstitial space. It appears whenever filtration outpaces lymph drainage. There are four main mechanisms.
Figure 4 · Four ways to make oedema
Inflammation deserves special mention. In acute injury, the number of large pores in capillary walls rises, and Levick and Michel showed that even a small rise dramatically increases filtration [1]. That is why an acute sprain swells within minutes.
| Feature | What to check | What it suggests |
|---|---|---|
| Distribution | One limb or both; localised or general | One limb: local cause, such as injury, DVT or lymphatic damage. Both: often systemic, such as heart, liver or kidney |
| Pitting | Press firmly for several seconds and release | Pitting: mobile fluid. Little or no pitting: long-standing lymphoedema with fibrosis |
| Stemmer sign | Try to pinch a fold of skin over the base of the second toe or finger | Cannot pinch: suggests lymphoedema |
| Skin | Colour, temperature, thickening, tightness | Warm, red and tender: possible infection or DVT |
| Measurement | Circumference at marked points, or limb volume | Track change over time |
Red flags before treating swelling
A newly swollen, warm, painful calf may be a deep vein thrombosis. Sudden swelling with breathlessness may be heart failure. Spreading redness with fever may be cellulitis. Refer these for medical review before applying massage or compression.
Lymphoedema is swelling caused by failure of the lymphatic system. It may be primary, from an inherited defect, or secondary, after lymph node removal, radiotherapy, infection such as filariasis, or trauma. Because protein-rich fluid accumulates, the tissue gradually thickens and becomes fibrous.
Breast cancer treatment is a common cause in clinical practice. More than one in five patients treated for breast cancer develop arm lymphoedema [3].
Complex decongestive therapy combines four elements: manual lymphatic drainage (MLD), compression, skin care and exercise. The first phase reduces swelling; the second maintains the reduction [3].
Figure 5 · What helps lymphoedema
The Cochrane review by Ezzo and colleagues found that compression bandaging alone reduced excess volume by 30–38.6%. Adding MLD gave a further 7.11% [3]. People with mild-to-moderate lymphoedema seemed to respond best, and MLD was safe in all trials [3].
Exercise was long discouraged for fear of making swelling worse. In a one-year trial, Schmitz and colleagues randomised 141 women with stable arm lymphoedema to slowly progressive weight lifting or usual care [4].
Swelling did not increase. Flare-ups fell from 29% to 14%, symptoms improved and strength increased [4]. Participants wore a well-fitted compression garment while lifting [4].
| Situation | Mechanism | First-line approach |
|---|---|---|
| Swollen ankle after a sprain | Leaky capillaries from inflammation [1] | Protect, elevate, compress, early movement |
| Both ankles swollen in an older adult with breathlessness | Raised capillary pressure, possibly heart failure | Medical review; do not simply compress |
| Arm swelling after axillary node removal | Lymphatic failure | Compression; MLD; progressive exercise [3, 4] |
| Hot, swollen, painful calf | Possible deep vein thrombosis | Urgent medical referral |
Describe the formation and circulation of lymph. Add a note on oedema.
Fluid filters at the arterial end and is reabsorbed at the venous end. People with lymphoedema should avoid lifting.
Filtration usually continues along the capillary, with lymph returning the excess; the glycocalyx is the key barrier [1, 2].
Compression is the core of lymphoedema treatment, with MLD adding a small extra effect [3]. Progressive weight lifting does not worsen swelling and reduces flare-ups [4].
Identify the mechanism first, rule out red flags, then use elevation, movement and compression to help the lymphatics do their job.
10 questions on this page. Tap one to see the answer and the reasoning.
Answer: (B) Absorption is transient in most tissues; slight filtration prevails even in venules [1].
Answer: (B) The glycocalyx is recognised as the semipermeable layer of the endothelium [1, 2].
Answer: (B) Filtered fluid returns to the circulation as lymph [2].
Answer: (C) Sinusoids have wide gaps; in specialised regions exchange differs from continuous capillaries [1].
Answer: (B) Modelling shows small rises in large-pore numbers dramatically increase filtration in inflammation [1].
Answer: (B) This is the ‘no absorption’ rule of the revised Starling equation [2].
Answer: (B) MLD added a mean 7.11% reduction to bandaging, which alone achieved 30–38.6% [3].
Answer: (B) Subgroup analysis suggested mild-to-moderate cases respond better [3].
Answer: (B) Swelling was unchanged, flare-ups fell from 29% to 14% and strength improved [4].
Answer: (B) A fitted compression garment was worn during lifting [4].
Key takeaways
| Source | Why it earns its place |
|---|---|
| Levick JR, Michel CC — Cardiovascular Research, 2010 | The revised Starling principle explained [1] |
| Woodcock TE, Woodcock TM — British Journal of Anaesthesia, 2012 | Clinical consequences of the glycocalyx model [2] |
| Ezzo J et al. — Cochrane Review, 2015 | Evidence on manual lymphatic drainage [3] |
| Schmitz KH et al. — NEJM, 2009 | The trial that changed exercise advice in lymphoedema [4] |
Reviewed by the Physiotherapist India Team. · Human Physiology contents