New method for evaluation of lung lymph flow rate with intact lymphatics in anaesthetized sheep

An in silico approach to understanding the interaction between cardiovascular and pulmonary lymphatic dysfunction

The lung is extremely sensitive to interstitial fluid balance, yet the role of pulmonary lymphatics in lung fluid homeostasis and its interaction with cardiovascular pressures is poorly understood. In health, there is a fine balance between fluid extravasated from the pulmonary capillaries into the interstitium and the return of fluid to the circulation via the lymphatic vessels. This balance is maintained by an extremely interdependent system governed by pressures in the fluids (air and blood) and tissue (interstitium), lung motion during breathing, and the permeability of the tissues. Chronic elevation in left atrial pressure (LAP) due to left heart disease increases the capillary blood pressure. The consequent fluid accumulation in the delicate lung tissue increases its weight, decreases its compliance, and impairs gas exchange. This interdependent system is difficult, if not impossible, to study experimentally. Computational modeling provides a unique perspective to analyze fluid movement in the cardiopulmonary vasculature in health and disease. We have developed an initial in silico model of pulmonary lymphatic function using an anatomically structured model to represent ventilation and perfusion and underlying biophysical laws governing fluid transfer at the interstitium. This novel model was tested against increased LAP and noncardiogenic effects (increased permeability). The model returned physiologically reasonable values for all applications, predicting pulmonary edema when LAP reached 25 mmHg and with increased permeability.NEW & NOTEWORTHY This model presents a novel approach to understanding the interaction between cardiac dysfunction and pulmonary lymphatic function, using anatomically structured models and biophysical equations to estimate regional variation in fluid transport from blood to interstitial and lymphatic flux. This fluid transport model brings together advanced models of ventilation, perfusion, and lung mechanics to produce a detailed model of fluid transport in health and various altered pathological conditions.

Microparticle image velocimetry approach to flow measurements in isolated contracting lymphatic vessels

We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ -PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ -PIV technique in these vessels.

Lymphatics and lymph in acute lung injury

PURPOSE OF REVIEW

Lymph flow will be discussed as part of the drainage and fluid balance of lung tissue and abdomen as well as a qualitative analysis of inflammatory processes.

RECENT FINDINGS

Measurement of lung lymph is still a technical challenge. Mechanical ventilation and positive end-expiratory pressure impede lung lymph flow by increased intrathoracic pressure and increased central venous pressure. Positive end-expiratory pressure may thus enhance edema formation of the lung. Inflammatory spread from abdomen to the lung via the lymphatic system has been shown in a number of experimental studies. Ligation or diversion of the thoracic duct has been proposed to blunt the effects of noxious stimuli mediated by lymphatics to the lungs. Lymphatics have a major role on abdominal fluid balance while draining extravascular fluid accumulation and edema, especially during sepsis. Mechanical ventilation with high airway pressure increases abdominal edema (ascites) and spontaneous breathing protects from edema formation.

SUMMARY

Lymph flow measurements are still a difficult task to perform; however, new results show an important function in the fluid balance of the lung and abdomen. Inflammatory spread may occur from the lung to the periphery by the blood stream and from the abdomen to the lung by lymph flow.

A Multi-Scale Model of Dendritic Cell Education and Trafficking in the Lung: Implications for T Cell Polarization

Health Sciences face a significant challenge in translating basic science data into improved understanding of innate and adaptive immunity. To improve understanding of the dynamic role of dendritic cells in the lung, a mathematical model was developed using a physiologically structured framework that explicitly accounts for functional heterogeneity. As sentinels of the immune system, dendritic cells play critical roles in coupling innate to adaptive immunity and produce an important immune regulatory cytokine: IL-12. The term IL-12 actually refers to the net bioactivity of three related proteins; IL12p40, IL12p70, and IL12(p40)2; assembled from two independent gene products: p35 and p40. The model for dendritic cell education and trafficking was created by incorporating five dimensions: chronological time, maturational age, p35 signal, p40 signal, and spatial location. The computational framework was calibrated to and validated against appropriate experimental studies. Using this validated model, I explore the impact of dynamic changes in the lung epithelium of IL-4, IFN-gamma, and PGE2 on the dynamic ability of dendritic cells to polarize T cell subsets. In summary, this multi-scale model provides an essential aid in understanding the impact of a dynamically changing lung microenvironment on the ability of dendritic cells to orchestrate adaptive immunity.