The effects of gravity and compression on interstitial fluid transport in the lower limb

Abstract

Edema in the limbs can arise from pathologies such as elevated capillary pressures due to failure of venous valves, elevated capillary permeability from local inflammation, and insufficient fluid clearance by the lymphatic system. The most common treatments include elevation of the limb, compression wraps and manual lymphatic drainage therapy. To better understand these clinical situations, we have developed a comprehensive model of the solid and fluid mechanics of a lower limb that includes the effects of gravity. The local fluid balance in the interstitial space includes a source from the capillaries, a sink due to lymphatic clearance, and movement through the interstitial space due to both gravity and gradients in interstitial fluid pressure (IFP). From dimensional analysis and numerical solutions of the governing equations we have identified several parameter groups that determine the essential length and time scales involved. We find that gravity can have dramatic effects on the fluid balance in the limb with the possibility that a positive feedback loop can develop that facilitates chronic edema. This process involves localized tissue swelling which increases the hydraulic conductivity, thus allowing the movement of interstitial fluid vertically throughout the limb due to gravity and causing further swelling. The presence of a compression wrap can interrupt this feedback loop. We find that only by modeling the complex interplay between the solid and fluid mechanics can we adequately investigate edema development and treatment in a gravity dependent limb.

The Metabolic Syndrome, a Human Disease

“…In classical (or clinical) Celsus-like inflammation, the increase in blood flow brings more oxygen, nutrients, and defense-related cells to the affected site in order to fight against alien interference and, later, promote/allow for recovery and restoration [369]. The interstitial space is optimal for the strategic movement of phagocytic cells, or access by immune-system molecules, because of the possibility of maintaining/restraining all components within a limited space or 'killing field' [370,371], corralling inside too the microbes or foreign objects provoking the tissue reaction. The resolution of inflammation often includes the accumulation of debris and its progressive (also phagocytic) elimination [372] up to the recovery of normalcy [373,374].…”

Intelligent Syringe for Porous Tissue Characterization Using Advanced Darcy Flow Pressure Transient Analysis

“…Investigators have speculated that high pressure damage at injection zones may lead to inflammation and permeability increases as flow increases from capillaries to surrounding tissues. Permeability issues of significance to iSyringe applications are discussed in recent studies 4,5,6,7 . For example, the latter explores "elevated capillary permeability," "increases in hydraulic conductivity" and "increased tissue permeability" using finite element solutions to lower limb swelling.…”

Computational simulations of the effects of gravity on lymphatic transport

“…Previously, we demonstrated how the dynamics of nitric oxide (NO) (produced by shear stress on lymphatic endothelial cells) and intracellular calcium fluxes in lymphatic muscle cells can establish feedback that controls lymphatic contractions ( 31–33 ). We have also considered the effects of gravity on the fluid balance in the lower leg at the scale of the entire limb using a simplified model of lymphatic pumping ( 57 ), but did not address the pumping dynamics of individual lymph vessels. Here, we analyze how gravitational force (i.e.…”