Tonometry of Deep Tissues for Setting Effective Compression Pressures in Lymphedema of Limbs

Abstract

Deep tissue tonometry of limbs is useful for setting IPC devices at compression pressures for mobilizing edema fluid.

Indentation of a circular membrane on an incompressible liquid

“…The proposed model may roughly correspond to the indentation test of a very soft subcutaneous tissue covered by skin. Therefore, the results of the simulations are illustrated assuming a range of material parameters (thickness and stiffness of skin) and performance parameters (indentation depth and indenter radius) appropriate for deep tonometry [26]. In all the cases considered, the following parameters are used: the radius of the indenter a = 5.5 mm, the thickness of the undeformed membrane h 0 = 1 mm, and the membrane's outer radius R e = 0.05 m. Selection of this radius is motivated by clinical observations, which show that a few centimeters from the indenter no visible tissue deformations can be seen.…”

“…where λ s0 = λ s (R 0 ), λ ϕ0 = λ ϕ (R 0 ), and α 0 = α(R 0 ). Taking into account the usefulness of using the indentation test as the method for the identification of the material properties of the membrane, the dependence of the total indentation force F and pressure P 0 on the elastic constant E in the range roughly corresponding to the stiffness of skin tissue, i.e., between 0.01 and 10 MPa [9], and the indentation depth z 0 applied for deep tonometry [26] are presented in Figs. 7 and 8.…”

“…The difference is smaller but also noticeable for the indentation force, especially for high values of Young's modulus and large indentation depths. The assumed size of the indenter is relatively large, as it is used for deep tonometry [26]; in other cases, when the indenter is smaller, the difference between solutions should decrease.…”

“…The identified properties may refer to cells, tissues, or organs and express elastic or viscoelastic parameters as well as permeability. The indentation depth can be of the order of nanometers [18] or micrometers [16,25], and millimeters [7,22] up to one centimeter [26]. In some of the solutions, forces are controlled, and in others, penetration and speed are controlled.…”

“…As a result for physiologically acceptable loads applied in tonometry deformations of muscles and bones caused by an indenter compared to deformations of skin and subcutaneous tissue are small and in the first approximation can be neglected. In the simplest version of the deep tonometry (see [26]), a dynamometer equipped with a flat cylindrical tip, with a surface area of 1 cm 2 , is pressed against the tissue at a constant rate of approximately 1 mm/s to the depth of 1 cm. The maximum force is recorded and is used as a descriptor of a state of the tissue.…”