The Revised Starling Principle and Its Role in Lymphedema

Introduction

The Starling principle, originally proposed by Ernest Starling in the early 1900s, has been a critical theory in understanding fluid exchange between blood vessels and tissues. However, recent advancements have led to a revised understanding of this principle, which has significant implications for the management of lymphedema. 

The Original Starling Principle

The original Starling principle suggests that fluid movement across capillary walls is governed by the balance of hydrostatic and oncotic pressures. Hydrostatic pressure pushes fluid out of the capillaries, while oncotic pressure pulls fluid back in.

This balance ensures that fluid is filtered out of the capillaries at the arterial end and reabsorbed at the venous end. It was previously understood that much of the interstitial fluid was reabsorbed by the venous system, and only 10-20% was handled by the lymphatic system.

The Revised Starling Principle

While the original Starling principle gave us an insight into fluid movement across a semipermeable membrane, recent research has highlighted the importance of the endothelial glycocalyx layer (EGL) in fluid regulation.

The revised Starling principle, introduced in 2010, acknowledges that microvessels are permeable to macromolecules, which means that a balance of pressures alone cannot halt fluid exchange. The EGL acts as a semi-permeable barrier, playing a crucial role in regulating fluid movement. Fluid crosses the capillary wall, bringing cellular waste and debris with it because of the pressure along the capillary wall.  Because of the hair-like structures of the EGL, an “exclusion zone” is created, where permeability is reduced.

The Revised Starling Principle and Lymphedema

Lymphedema is characterized by the accumulation of lymphatic fluid in the tissues, leading to swelling. The revised Starling principle provides a better understanding of the mechanisms underlying fluid accumulation and offers new insights into the management of lymphedema. With this new information, it can be understood that the lymphatic system is responsible for virtually 100% of interstitial fluid return to the vascular system, not the previously thought 10-20%. By considering the role of the EGL and the permeability of microvessels, physicians can develop more effective treatment strategies for patients with lymphedema. 

The revised Starling principle underscores the previously underappreciated significance of the lymphatic system in fluid homeostasis and pathology. It demonstrates that the lymphatic system plays a crucial role in managing interstitial fluid, thus highlighting its importance in preventing and treating conditions like lymphedema. This deeper understanding prompts a more integrated approach to treatment, emphasizing the need for therapies that support both vascular and lymphatic health. As of now, the revised Starling principle is not part of mainstream medical education, and practitioners often are left without an appreciation of the importance of the lymphatic system in fluid homeostasis, as well as the related complications of lymphatic disease.   

The revised Starling principle represents a significant advancement in our understanding of fluid exchange and its role in conditions such as lymphedema. By incorporating the latest research on the EGL and fluid movement out of the circulatory system into the lymphatic system, physicians can improve the diagnosis and treatment of lymphedema, ultimately creating improved patient outcomes. 

What Does This Mean for Your Practice and Patient Care?

Understanding the vital role of the lymphatic system and its role in infection response and wound healing helps place the spotlight on swelling that you see in your patients. Gathering additional information from your patient, especially regarding the onset of swelling, resolution of symptoms overnight with gravity eliminated positioning, feelings of heaviness/fullness, inability to wear regular shoes or clothes and any other concerning symptoms.

A thorough examination and documentation of skin changes noted is also critical, including thickened or dry skin, color changes, blisters, papillomas, pitting or non-pitting edema, non-healing wounds or any other skin changes of note.

All swelling is due to a dysfunction of the lymphatic system, it is just differentiated by whether it is a reversible or irreversible dysfunction.  Patients with lymphatic dysfunction are at higher risk for developing infection/cellulitis as well as ongoing difficulties with wound healing.  Intervention early in the process of lymphedema leads to decreased risk of infection, chronic inflammation and tissue hardening. Untreated lymphedema can also lead to a loss of independence and difficulties with performing activities of daily living, as well as psychological effects of depression, anxiety and frustration. Often patients will isolate themselves at home, embarrassed by large legs and feet or weeping open wounds.

Many patients have great difficulty finding a physician who can diagnose and offer treatment for lymphedema, leading to delays in care and ongoing complications as well as frustration on the part of the patient.

Patient Case Study

I recently had a patient in the lymphedema clinic who sums up this frustrating cycle well.

A 76-year-old female presented to the lymphedema clinic for evaluation and treatment. The patient was originally seen by her primary care physician with a complaint of red skin and itchy rash on shins as well as swelling in lower legs, ankles and feet. PCP referred this patient to a vascular practice for evaluation.

After examination, the patient was told her circulation was fine. Vascular then referred to dermatology, who experimented with many different creams and ointments, none of which cleared the patient’s itching and redness.

The patient confided to me “you should see my countertop and all the lotions I have on it!”Dermatology then referred to rheumatology, who cleared the patient from their standpoint and referred to lymphedema clinic.

Conclusion

All swelling that you see in your clinic is relevant, and the earlier you are able to intervene, the less likely you will see the chronic inflammation and skin changes that accompany the later stages of lymphedema.  Compression and referral to lymphedema specialists can assist with wound healing, infection prevention and better overall outcomes for your patients.   

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