Characterization of cutaneous oedema : modelling and mesurements methods

Sammanfattning: Three different methods have been developed to characterize oedema. The methods can be applied on any site of the skin to study the effect of oedema on the mechanical properties of the skin. Changes in the viscoelastic properties of the oedematous tissues after treatment can be monitored by these methods. Thus effectiveness of the treatment, and improvement of elastic and viscoelastic properties of the oedematous tissues can be determined by the methods described.Mechanical Impedance (MI) describes viscoelastic properties of tissues subjected to external deformation. Differences in the MI between normal and oedematous tissues were greater at lower frequencies. Mechanical pulse wave propagation, MPWP was measured in gel, normal and oedematous tissues. The MPWP depended on the density of the gel and on the elasticity and viscosity of the tissues, and differed from oedematous to nonoedematous tissues.An instrument was developed which rapidly compressed the skin and recorded the force, which decreased as the fluid translocated. Normal subjects and oedematous patients showed marked differences in the pattern of fluid translocation. The flow rate and the total volume flow varied with the degree of oedema. Force curves obtained from patients, who were given pneumatic compression treatment for unilateral post-mastectomy lymphoedema were analysed. Mathematical expressions for the curves were found to define the degree of oedema.An analogue electrical model which demonstrates the viscoelastic nature of oedematous tissue under compression has been proposed.The model consists of the electrical counterparts of multicompartment arrangements of springs and dashpots.The model elements were assigned values from experimental results. The models were tested by a computer simulation and the results show viscoelastic behaviour similar to that obtained from the measurement of fluid translocation in tissue under compression.