Constitutively Enhanced Lymphatic Pumping in the Upper Limbs of Women Who Later Develop Breast Cancer-Related Lymphedema

Loss of anoctamin 1 reveals a subtle role for BK channels in lymphatic muscle action potentials

Ca2+ signalling plays a crucial role in determining lymphatic muscle cell excitability and contractility through its interaction with the Ca2+-activated Cl- channel anoctamin 1 (ANO1). In contrast, the large-conductance (BK) Ca2+-activated K+ channel (KCa) and other KCa channels have prominent vasodilatory actions by hyperpolarizing vascular smooth muscle cells. Here, we assessed the expression and contribution of the KCa family to mouse and rat lymphatic collecting vessel contractile function. The BK channel was the only KCa channel consistently expressed in fluorescence-activated cell sorting-purified mouse lymphatic muscle cell lymphatic muscle cells. We used a pharmacological inhibitor of BK channels, iberiotoxin, and small-conductance Ca2+-activated K+ channels, apamin, to inhibit KCa channels acutely in ex vivo isobaric myography experiments and intracellular membrane potential recordings. In basal conditions, BK channel inhibition had little to no effect on either mouse inguinal-axillary lymphatic vessel (MIALV) or rat mesenteric lymphatic vessel contractions or action potentials (APs). We also tested BK channel inhibition under loss of ANO1 either by genetic ablation (Myh11CreERT2-Ano1 fl/fl, Ano1ismKO) or by pharmacological inhibition with Ani9. In both Ano1ismKO MIALVs and Ani9-pretreated MIALVs, inhibition of BK channels increased contraction amplitude, increased peak AP and broadened the peak of the AP spike. In rat mesenteric lymphatic vessels, BK channel inhibition also abolished the characteristic post-spike notch, which was exaggerated with ANO1 inhibition, and significantly increased the peak potential and broadened the AP spike. We conclude that BK channels are present and functional on mouse and rat lymphatic muscle cells but are otherwise masked by the dominance of ANO1. KEY POINTS: Mouse and rat lymphatic muscle cells express functional BK channels. BK channels make little contribution to either rat or mouse lymphatic collecting vessel contractile function in basal conditions across a physiological pressure range. ANO1 limits the peak membrane potential achieved in the action potential and sets a plateau potential limiting the voltage-dependent activation of BK. BK channels are activated when ANO1 is absent or blocked and slightly impair contractile strength by reducing the peak membrane potential achieved in the action potential spike and accelerating the post-spike repolarization.

Revolutionizing lymph node metastasis imaging: the role of drug delivery systems and future perspectives

The deployment of imaging examinations has evolved into a robust approach for the diagnosis of lymph node metastasis (LNM). The advancement of technology, coupled with the introduction of innovative imaging drugs, has led to the incorporation of an increasingly diverse array of imaging techniques into clinical practice. Nonetheless, conventional methods of administering imaging agents persist in presenting certain drawbacks and side effects. The employment of controlled drug delivery systems (DDSs) as a conduit for transporting imaging agents offers a promising solution to ameliorate these limitations intrinsic to metastatic lymph node (LN) imaging, thereby augmenting diagnostic precision. Within the scope of this review, we elucidate the historical context of LN imaging and encapsulate the frequently employed DDSs in conjunction with a variety of imaging techniques, specifically for metastatic LN imaging. Moreover, we engage in a discourse on the conceptualization and practical application of fusing diagnosis and treatment by employing DDSs. Finally, we venture into prospective applications of DDSs in the realm of LNM imaging and share our perspective on the potential trajectory of DDS development.

Superficial and functional imaging of the tricipital lymphatic pathway: a modern reintroduction

PURPOSE

The tricipital, or Caplan's, lymphatic pathway has been previously identified in cadavers and described as a potential compensatory pathway for lymphatic drainage of the upper extremity, as it may drain lymphatic fluid directly to the scapular lymph nodes, avoiding the axillary lymph node groups. The aim of this study was to map the anatomy of the tricipital pathway in vivo in patients without lymphatic disease.

METHODS

A retrospective review was performed to identify patients with unilateral breast cancer undergoing preoperative Indocyanine green (ICG) lymphography prior to axillary lymph node dissection from May 2021 through January 2022. Exclusion criteria were evidence or known history of upper extremity lymphedema or non-linear channels visualized on ICG. Demographic, oncologic, and ICG imaging data were extracted from a Lymphatic Surgery Database. The primary outcome of this study was the presence and absence of the tricipital pathway. The secondary outcome was major anatomical variations among those with a tricipital pathway.

RESULTS

Thirty patients underwent preoperative ICG lymphography in the study period. The tricipital pathway was visualized in the posterior upper arm in 90% of patients. In 63% of patients, the pathway had a functional connection to the forearm (long bundle variant) and in 27%, the pathway was isolated to the upper arm without a connection to the forearm (short bundle variant). In those with a long bundle, the contribution was predominantly from the posterior ulnar lymphosome. Anatomic destinations of the tricipital pathway included the deltotricipital groove and the medial upper arm channel, which drains to the axilla.

CONCLUSION

When present, the tricipital pathway coursed along the posterior upper arm with variability in its connections to the forearm distally, and the torso proximally. Long-term follow-up studies will help determine the significance of these anatomic variations in terms of individual risk of lymphedema after axillary nodal dissection.

Is Lymphedema a Systemic Disease? A Paired Molecular and Histological Analysis of the Affected and Unaffected Tissue in Lymphedema Patients

Secondary lymphedema is a chronic, debilitating disease and one of the most common side effects of oncologic surgery, substantially decreasing quality of life. Despite the progress conducted in lymphedema research, the underlying pathomechanisms remain elusive. Lymphedema is considered to be a disease affecting an isolated extremity, yet imaging studies suggest systemic changes of the lymphatic system in the affected patients. To evaluate potential systemic manifestations in lymphedema, we collected matched fat and skin tissue from the edematous and non-edematous side of the same 10 lymphedema patients as well as anatomically matched probes from control patients to evaluate whether known lymphedema manifestations are present systemically and in comparison to health controls. The lymphedematous tissue displayed various known hallmarks of lymphedema compared to the healthy controls, such as increased epidermis thickness, collagen deposition in the periadipocyte space and the distinct infiltration of CD4+ cells. Furthermore, morphological changes in the lymphatic vasculature between the affected and unaffected limb in the same lymphedema patient were visible. Surprisingly, an increased collagen deposition as well as CD4 expression were also detectable in the non-lymphedematous tissue of lymphedema patients, suggesting that lymphedema may trigger systemic changes beyond the affected extremity.

Recent advancement of imaging strategies of the lymphatic system: Answer to the decades old questions

The role of the lymphatic system in maintaining tissue homeostasis and a number of different pathophysiological conditions has been well established. The complex and delicate structure of the lymphatics along with the limitations of conventional imaging techniques make lymphatic imaging particularly difficult. Thus, in-depth high-resolution imaging of lymphatic system is key to understanding the progression of lymphatic diseases and cancer metastases and would greatly benefit clinical decisions. In recent years, the advancement of imaging technologies and development of new tracers suitable for clinical applications has enabled imaging of the lymphatic system in both clinical and pre-clinical settings. In this current review, we have highlighted the advantages and disadvantages of different modern techniques such as near infra-red spectroscopy (NIRS), positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI) and fluorescence optical imaging, that has significantly impacted research in this field and has led to in-depth insights into progression of pathological states. This review also highlights the use of current imaging technologies, and tracers specific for immune cell markers to identify and track the immune cells in the lymphatic system that would help understand disease progression and remission in immune therapy regimen.

Imaging technology of the lymphatic system

The lymphatic system plays critical roles in tissue fluid homeostasis and immunity and has been implicated in the development of many different pathologies, ranging from lymphedema, the spread of cancer to chronic inflammation. In this review, we first summarize the state-of-the-art of lymphatic imaging in the clinic and the advantages and disadvantages of these existing techniques. We then detail recent progress on imaging technology, including advancements in tracer design and injection methods, that have allowed visualization of lymphatic vessels with excellent spatial and temporal resolution in preclinical models. Finally, we describe the different approaches to quantifying lymphatic function that are being developed and discuss some emerging topics for lymphatic imaging in the clinic. Continued advancements in lymphatic imaging technology will be critical for the optimization of diagnostic methods for lymphatic disorders and the evaluation of novel therapies targeting the lymphatic system.

The impact of monitoring techniques on progression to chronic breast cancer-related lymphedema: a meta-analysis comparing bioimpedance spectroscopy versus circumferential measurements

BACKGROUND

Chronic breast cancer-related lymphedema (BCRL) is a potentially serious complication following treatment. Monitoring for progression to BCRL may allow for earlier detection and intervention, reducing the rate of progression to chronic BCRL. Therefore, the purpose of this meta-analysis is to evaluate the impact of monitoring techniques on the incidence of chronic BCRL among patients monitored by bioimpedance spectroscopy (BIS) and circumference as compared to background rates.

METHODS

Eligible peer-reviewed studies from PubMed, CINHAL, or Google Scholar that were published in English from 2013 onward and conducted in North America, Europe, or Oceania. Incidence rates abstracted from studies were classified by BCRL monitoring method: background (no standardized BIS or circumference assessments), BIS or circumference. A random-effects model was used to calculate a pooled annualized estimate of BCRL incidence while accounting for clinical and methodological heterogeneity. Subgroup analyses examined differences in duration of follow-up as well as breast and axillary surgery.

RESULTS

50 studies were included, representing over 67,000 women. The annualized incidence of BCRL was 4.9% (95% CI: 4.3-5.5) for background studies (n = 35), 1.5% (95% CI: 0.6-2.4) for BIS-monitored studies (n = 7), and 7.7% (95% CI: 5.6-9.8) for circumference-monitored studies (n = 11). The cumulative BCRL incidence rate in BIS-monitored patients was 3.1% as compared to 12.9% with background monitoring (69% reduction) and 17.0% with circumference-monitored patients (81% reduction).

CONCLUSIONS

Evidence suggests that monitoring with BIS allowing for early intervention significantly reduces the relative risk of chronic BCRL with a 69% and 81% reduction compared to background and circumference, respectively. Circumference monitoring did not appear to provide a benefit with respect to chronic BCRL incidence. Based on these results, BIS should be considered for BCRL screening in order to detect subclinical BCRL and reduce rates of chronic BCRL, particularly in high-risk patients.

Lymphatic Valves and Lymph Flow in Cancer-Related Lymphedema

Lymphedema is a complex disease caused by the accumulation of fluid in the tissues resulting from a dysfunctional or damaged lymphatic vasculature. In developed countries, lymphedema most commonly occurs as a result of cancer treatment. Initially, impaired lymph flow causes edema, but over time this results in inflammation, fibrotic and fatty tissue deposition, limited mobility, and bacterial infections that can lead to sepsis. While chronically impaired lymph flow is generally believed to be the instigating factor, little is known about what pathophysiological changes occur in the lymphatic vessels to inhibit lymph flow. Lymphatic vessels not only regulate lymph flow through a variety of physiologic mechanisms, but also respond to lymph flow itself. One of the fascinating ways that lymphatic vessels respond to flow is by growing bicuspid valves that close to prevent the backward movement of lymph. However, lymphatic valves have not been investigated in cancer-related lymphedema patients, even though the mutations that cause congenital lymphedema regulate genes involved in valve development. Here, we review current knowledge of the regulation of lymphatic function and development by lymph flow, including newly identified genetic regulators of lymphatic valves, and provide evidence for lymphatic valve involvement in cancer-related lymphedema.

Lymphatic remodelling in response to lymphatic injury in the hind limbs of sheep

Contractile activity in the lymphatic vasculature is essential for maintaining fluid balance within organs and tissues. However, the mechanisms by which collecting lymphatics adapt to changes in fluid load and how these adaptations influence lymphatic contractile activity are unknown. Here we report a model of lymphatic injury based on the ligation of one of two parallel lymphatic vessels in the hind limb of sheep and the evaluation of structural and functional changes in the intact, remodelling lymphatic vessel over a 42-day period. We show that the remodelled lymphatic vessel displayed increasing intrinsic contractile frequency, force generation and vessel compliance, as well as decreasing flow-mediated contractile inhibition via the enzyme endothelial nitric oxide synthase. A computational model of a chain of lymphatic contractile segments incorporating these adaptations predicted increases in the flow-generation capacity of the remodelled vessel at the expense of normal mitochondrial function and elevated oxidative stress within the lymphatic muscle. Our findings may inform interventions for mitigating lymphatic muscle fatigue in patients with dysfunctional lymphatics.

A novel mouse tail lymphedema model for observing lymphatic pump failure during lymphedema development

It has been suggested that many forms of secondary lymphedema in humans are driven by a progressive loss of lymphatic pump function after an initial risk-inducing event. However, the link between pump failure and disease progression has remained elusive due to experimental challenges in the clinical setting and a lack of adequate animal models. Using a novel surgical model of lymphatic injury, we track the adaptation and functional decline of the lymphatic network in response to surgery. This model mimics the histological hallmarks of the typical mouse tail lymphedema model while leaving an intact collecting vessel for analysis of functional changes during disease progression. Lymphatic function in the intact collecting vessel negatively correlated with swelling, while a loss of pumping pressure generation remained even after resolution of swelling. By using this model to study the role of obesity in lymphedema development, we show that obesity exacerbates acquired lymphatic pump failure following lymphatic injury, suggesting one mechanism through which obesity may worsen lymphedema. This lymphatic injury model will allow for future studies investigating the molecular mechanisms leading to lymphedema development.

T helper 2 differentiation is necessary for development of lymphedema

T cells infiltrating lymphedematous tissues have a mixed T helper 1 (Th1) and Th2 differentiation profile. Treatment with neutralizing antibodies targeting cytokines that promote Th2 differentiation (interleukin 4 [IL-4] and IL-13) decreases the severity of lymphedema in preclinical models, suggesting that Th2 cells play a key role in the pathology of this disease. However, these previous studies do not address the contribution of Th1 cells and it remains unknown if IL-4 and IL-3 blockade acts primarily on T cells or decreases the pathological changes of lymphedema by other mechanisms. Therefore, this study sought to analyze the effect of lymphatic injury in transgenic mice with mutations that cause defects in Th1 and Th2 cell generation (T-bet knockout or T-betKO and STAT6 knockout or STAT6KO mice, respectively). Using both the mouse tail and popliteal lymph node dissection models of lymphedema, we show that Th2-deficient (STAT6KO) mice are protected from developing lymphedema, have decreased fibrosis, increased collateral vessel formation, and preserved collecting lymphatic vessel pumping function. In contrast, mice with defective Th1 cell generation (T-betKO) develop disease with the same severity as wild-type controls. Taken together, our results suggest that Th2 differentiation is necessary for development of lymphedema following lymphatic injury and that Th1 differentiation does not significantly contribute to the pathology of the disease. Such findings are important as immunotherapy directed at Th2 cells has been found to be effective in well-studied Th2-mediated diseases such as asthma and atopic dermatitis and may therefore be similarly useful for lymphedema management.

Cancer-associated secondary lymphoedema

Lymphoedema is an oedematous condition with a specific and complex tissue biology. In the clinical context of cancer, the pathogenesis of lymphoedema ensues most typically from the modalities employed to stage and treat the cancer (in particular, surgery and radiotherapy). Despite advances in cancer treatment, lifelong lymphoedema (limb swelling and the accompanying chronic inflammatory processes) affects approximately one in seven individuals treated for cancer, although estimates of lymphoedema prevalence following cancer treatment vary widely depending upon the diagnostic criteria used and the duration of follow-up. The natural history of cancer-associated lymphoedema is defined by increasing limb girth, fibrosis, inflammation, abnormal fat deposition and eventual marked cutaneous pathology, which also increases the risk of recurrent skin infections. Lymphoedema can substantially affect the daily quality of life of patients, as, in addition to aesthetic concerns, it can cause discomfort and affect the ability to carry out daily tasks. Clinical diagnosis is dependent on comparison of the affected region with the equivalent region on the unaffected side and, if available, with pre-surgical measurements. Surveillance is indicated in this high-risk population to facilitate disease detection at the early stages, when therapeutic interventions are most effective. Treatment modalities include conservative physical strategies that feature complex decongestive therapy (including compression garments) and intermittent pneumatic compression, as well as an emerging spectrum of surgical interventions, including liposuction for late-stage disease. The future application of pharmacological and microsurgical therapeutics for cancer-associated lymphoedema holds great promise.

Baseline Lymphatic Dysfunction Amplifies the Negative Effects of Lymphatic Injury

BACKGROUND

Genetic mutations and obesity increase the risk of secondary lymphedema, suggesting that impaired lymphatic function before surgical injury may contribute to disease pathophysiology. Previous studies show that obesity not only decreases lymphatic function, but also markedly increases pathologic changes, such as swelling, fibroadipose deposition, and inflammation. However, although these reports provide circumstantial evidence supporting the hypothesis that baseline lymphatic defects amplify the effect of lymphatic injury, the mechanisms regulating this association remain unknown.

METHODS

Baseline lymphatic morphology, leakiness, pumping, immune cell trafficking, and local inflammation and fibroadipose deposition were assessed in wild-type and Prox1-haploinsufficient (Prox1) mice, which have previously been shown to have abnormal vasculature without overt evidence of lymphedema. In subsequent experiments, wild-type and Prox1 mice underwent popliteal lymph node dissection to evaluate the effect of lymphatic injury. Repeated testing of all variables was conducted 4 weeks postoperatively.

RESULTS

At baseline, Prox1 mice had dilated, leaky lymphatic vessels corresponding to low-grade inflammation and decreased pumping and transport function, compared with wild-type mice. Popliteal lymph node dissection resulted in evidence of lymphedema in both Prox1 and wild-type mice, but popliteal lymph node dissection-treated Prox1 mice had increased inflammation and decreased lymphatic pumping.

CONCLUSIONS

Subclinical lymphatic dysfunction exacerbates the pathologic changes of lymphatic injury, an effect that is multifactorial and related to increased lymphatic leakiness, perilymphatic accumulation of inflammatory cells, and impaired pumping and transport capacity. These findings suggest that preoperative testing of lymphatic function may enable clinicians to more accurately risk-stratify patients and design targeted preventative strategies.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Lymphatic drainage efficiency: a new parameter of lymphatic function

Background Following convection from blood capillaries, plasma proteins are transported to loco-regional lymph nodes in two stages: first, uptake into peripheral lymphatics, and second, transport to nodes. Purpose To introduce a new parameter of lymphatic function that quantifies stage 2 - lymphatic drainage efficiency (LDE). Material and Methods Percentage injected activity (IIQ) in ilio-inguinal nodes 150 min following subcutaneous foot web-space injection of Tc-99 m-nanocolloid was measured in 102 patients undergoing lymphoscintigraphy using a method in which a standard is placed by image guidance over the nodes. Percentage activity leaving the injection depot by 150 min ( k) was measured in 60/102 patients. LDE (%) = 100 × (IIQ/ k). Abnormal lymphoscintigraphy was defined qualitatively as: (i) no activity in ilio-inguinal nodes at 45 min or negligible activity at 150 min (delay); (ii) lymph diversion through skin and/or deep system; and (iii) focal tracer accumulation suggesting cellulitis. Results Scintigraphy was bilaterally normal in 82 limbs, unilaterally normal in 40 limbs and abnormal in 82 limbs. IIQ correlated with k in bilaterally normal (r = 0.86; n = 52), unilaterally normal (r = 0.67; n = 27), and abnormal (r = 0.82; n = 41) limbs. IIQ, k, and LDE were significantly lower in unilaterally normal (9.3 ± 5.4%, 13.8 ± 7.1%, and 65 ± 30%) compared with bilaterally normal limbs (15.4 ± 8.4% [ P > 0.0001], 18.3 ± 8.9% [ P = 0.025], and 84 ± 30% [ P = 0.01]). LDE was lower in limbs displaying skin diversion and/or delay. Conclusion LDE is a new quantitative index that has potential value in clinical research but requires further clinical evaluation. Abnormal quantitative indices indicate that limbs unilaterally normal on lymphoscintigraphy are not functionally normal.

New and Emerging Treatments for Lymphedema

Although nonoperative and operative treatments for lymphedema (LE) are well established, these procedures typically provide only partial relief from limb swelling, functional impairment, and the risk of cellulitis. The lack of a cure for LE, however, is due to an incomplete understanding of the underlying pathophysiological mechanisms, and current research efforts are focusing on elucidating these processes to provide new, targeted therapies for this prevalent disease for which there is no cure. This article reviews the current literature regarding the pathophysiological mechanisms that underlie LE, as well as new and emerging therapies for the condition.

Long term effects of manual lymphatic drainage and active exercises on physical morbidities, lymphoscintigraphy parameters and lymphedema formation in patients operated due to breast cancer: A clinical trial

PURPOSE

evaluate whether manual lymphatic drainage (MLD) or active exercise (AE) is associated with shoulder range of motion (ROM), wound complication and changes in the lymphatic parameters after breast cancer (BC) surgery and whether these parameters have an association with lymphedema formation in the long run.

METHODS

Clinical trial with 106 women undergoing radical BC surgery, in the Women's Integrated Healthcare Center-University of Campinas. Women were matched for staging, age and body mass index and were allocated to performed AE or MLD, 2 weekly sessions during one month after surgery. The wound was evaluated 2 months after surgery. ROM, upper limb circumference measurement and upper limb lymphoscintigraphy were performed before surgery, and 2 and 30 months after surgery.

RESULTS

The incidence of seroma, dehiscence and infection did not differ between groups. Both groups showed ROM deficit of flexion and abduction in the second month postoperative and partial recovery after 30 months. Cumulative incidence of lymphedema was 23.8% and did not differ between groups (p = 0.29). Concerning the lymphoscintigraphy parameters, there was a significant convergent trend between baseline degree uptake (p = 0.003) and velocity visualization of axillary lymph nodes (p = 0.001) with lymphedema formation. A reduced marker uptake before or after surgery predicted lymphedema formation in the long run (>2 years). None of the lymphoscintigraphy parameters were shown to be associated with the study group. Age ≤39 years was the factor with the greatest association with lymphedema (p = 0.009). In women with age ≤39 years, BMI >24Kg/m2 was significantly associated with lymphedema (p = 0.017). In women over 39 years old, women treated with MLD were at a significantly higher risk of developing lymphedema (p = 0.011).

CONCLUSION

Lymphatic abnormalities precede lymphedema formation in BC patients. In younger women, obesity seems to be the major player in lymphedema development and, in older women, improving muscle strength through AE can prevent lymphedema. In essence, MLD is as safe and effective as AE in rehabilitation after breast cancer surgery.

Donor-Site Lymphedema Following Lymph Node Transfer for Breast Cancer-Related Lymphedema: A Systematic Review of the Literature

Abstracts Background: Among current surgical options used for treating breast cancer-related lymphedema (BCRL), autologous lymph node transfer (ALNT) is shown to provide favorable results. However, postoperative donor-site lymphedema (DSL), following the lymphatic flap harvesting from the groin area, has already been reported. Our aim is to summarize the recent literature for evidence of DSL following an ALNT for BCRL.

METHODS AND RESULTS

A PubMed bibliographic search was performed for published studies evaluating donor-site complications following LNT in BCRL patients. We recorded demographic data of the patients, the type of flap used, the follow-up, the donor-site morbidity, and the diagnostic tests performed pre- and postoperatively. Statistical analysis was conducted to document any correlation between the incidence of DSL and the abovementioned recorded parameters. According to our results, 11 studies met the inclusion criteria. From a total of 189 patients, three cases with DSL of the lower limb were reported (1.6%). No statistically significant correlations were found.

CONCLUSION

ALNT has become increasingly popular and is considered an effective surgical option for treating BCRL of the upper limb. Although the incidence of postoperative DSL is low, insufficient data on patients' demographics, surgical details, and postoperative assessment do not allow extracting significant correlations. Meticulous technique of lymph node harvesting should be seriously considered to further minimize this infrequent but debilitating complication.

The relationship between lymphangion chain length and maximum pressure generation established through in vivo imaging and computational modeling

The intrinsic contraction of collecting lymphatic vessels serves as a pumping system to propel lymph against hydrostatic pressure gradients as it returns interstitial fluid to the venous circulation. In the present study, we proposed and validated that the maximum opposing outflow pressure along a chain of lymphangions at which flow can be achieved increases with the length of chain. Using minimally invasive near-infrared imaging to measure the effective pumping pressure at various locations in the rat tail, we demonstrated increases in pumping pressure along the length of the tail. Computational simulations based on a microstructurally motivated model of a chain of lymphangions informed from biaxial testing of isolated vessels was used to provide insights into the pumping mechanisms responsible for the pressure increases observed in vivo. These models suggest that the number of lymphangions in the chain and smooth muscle cell force generation play a significant role in determining the maximum outflow pressure, whereas the frequency of contraction has no effect. In vivo administration of nitric oxide attenuated lymphatic contraction, subsequently lowering the effective pumping pressure. Computational simulations suggest that the reduction in contractile strength of smooth muscle cells in the presence of nitric oxide can account for the reductions in outflow pressure observed along the lymphangion chain in vivo. Thus, combining modeling with multiple measurements of lymphatic pumping pressure provides a method for approximating intrinsic lymphatic muscle activity noninvasively in vivo while also providing insights into factors that determine the extent that a lymphangion chain can transport fluid against an adverse pressure gradient. NEW & NOTEWORTHY Here, we report the first minimally invasive in vivo measurements of the relationship between lymphangion chain length and lymphatic pumping pressure. We also provide the first in vivo validation of lumped parameter models of lymphangion chains previously developed through data obtained from isolated vessel testing.

An Important Role of VEGF-C in Promoting Lymphedema Development

Secondary lymphedema is a common complication after cancer treatment, but the pathomechanisms underlying the disease remain unclear. Using a mouse tail lymphedema model, we found an increase in local and systemic levels of the lymphangiogenic factor vascular endothelial growth factor (VEGF)-C and identified CD68⁺ macrophages as a cellular source. Surprisingly, overexpression of VEGF-C in a transgenic mouse model led to aggravation of lymphedema with increased immune cell infiltration and vascular leakage compared with wild-type littermates. Conversely, blockage of VEGF-C by overexpression of soluble VEGF receptor-3 reduced edema development, diminishing inflammation and blood vascular leakage. Similar findings were obtained in a hind limb lymph node excision lymphedema model. Flow cytometry analyses and immunofluorescence stainings in lymphedematic tissue showed that VEGF receptor-3 expression was restricted to lymphatic endothelial cells. Our data suggest that endogenous VEGF-C causes blood vascular leakage and fluid influx into the tissue, thus actively contributing to edema formation. These data may provide the basis for future clinical therapeutic approaches.

Preoperative Lymphedema-Related Risk Factors in Early-Stage Breast Cancer

BACKGROUND

Prolongation of survival in patients with breast cancer due to early diagnosis and modern methods of treatment has turned the attention on lymphedema, which is the most important morbidity secondary to the treatment of the disease. Determination of lymphedema and related risk factors in patients before a surgical intervention may provide protection for patients and early treatment. The aim of this study was to determine the presence of lymphedema before surgery by bioimpedance analysis in patients with breast cancer and to establish risk factors associated with lymphedema.

PATIENTS AND METHODS

A total of 277 patients who were diagnosed as having breast cancer, were planned to undergo a surgical intervention, and had no clinical lymphedema were included in the study. The presence of lymphedema was evaluated with clinical examination, measurement of arm circumference, and bioimpedance analysis.

RESULTS

Lymphedema was found in 59 (21.3%) patients with no detected differences in arm circumferences. A significant relationship was found between the presence of lymphedema and body mass index (BMI), number of positive lymph nodes, and capsule invasion of the tumor (p = 0.001, p = 0.003, p = 0.002, respectively). Multiple regression analysis revealed that BMI and the number of positive lymph nodes were independent variables (p = 0.024, p = 0.002). ROC curve analysis resulted in an increased risk of preoperative lymphedema when the number of positive lymph nodes was ≥8. Correlation analysis revealed a positive correlation between the number of positive lymph nodes and L-dex score (p = 0.001, r = 0.219).

CONCLUSION

Preoperative bioimpedance analysis demonstrated that ∼1/5 of the patients had subclinical lymphedema. Preoperative subclinical lymphedema is associated with obesity and the number of positive lymph nodes, and thus, treatment of the axilla in patients who are preoperatively detected to have subclinical lymphedema should be revised.