Investigation of Physiological Swelling on Conductivity Distribution in Lower Leg Subcutaneous Tissue by Electrical Impedance Tomography

In-vivoviscoelastic properties estimation in subcutaneous adipose tissue by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT)

In-vivoviscoelastic properties have been estimated in human subcutaneous adipose tissue (SAT) by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT) under the influence of external compressive pressure-P.Thepve-MTM predicts the ion concentration distributioncmod(t)by coupling the poroviscoelastic and mass transport model to describe the hydrodynamics, rheology, and transport phenomena inside SAT. Thew-EIT measures the time-difference conductivity distribution∆γ(t)in SAT resulted from the ion transport. Based on the integration, the two viscoelastic properties which are viscoelastic shear modulus of SATGvand relaxation time of SATτvare estimated by applying an iterative curve-fitting between the normalized average ion concentration distributioncˆmod(t)predicted frompve-MTM and the experimental normalized average ion concentration distributioncˆexp(t)derived fromw-EIT. Thein-vivoexperiments were conducted by applying external compressive pressure-Pon human calf boundary to induce interstitial fluid flow and ion movement in SAT. As a result, the value ofGvwas range from 4.9-6.3 kPa and the value ofτvwas range from 27.50-38.5 s with the value of average goodness-of-fit curve fittingR² > 0.76. These values ofGvandτvwere compared to the human and animal tissue from the literature in order to verify this method. The results frompve-MTM provide evidence thatGvandτvplay a role in the predicted value ofcˆmod.

Evaluation of the effectiveness of electrical muscle stimulation on human calf muscles via frequency difference electrical impedance tomography

Objectives. The human skeletal muscle responds immediately under electrical muscle stimulation (EMS), and there is an immediate physiological response in human skeletal muscle. Non-invasive quantitative analysis is at the heart of our understanding of the physiological significance of human muscle changes under EMS. Response muscle areas of human calf muscles under EMS have been detected by frequency difference electrical impedance tomography (fd-EIT).Approach. The experimental protocol consists of four parts: pre-training (pre), training (tra), post-training (post), and relaxation (relax) parts. The relaxation part has three relaxation conditions, which are massage relaxation (MR), cold pack relaxation (CR), and hot pack relaxation (HR).Main results. From the experimental results, conductivity distribution imagesσ^p(pmeans protocol = pre,tra,post,or relax) are clearly reconstructed byfd-EIT as response muscle areas, which are called theM₁response area (composed of gastrocnemius muscle) and theM₂response area (composed of the tibialis anterior muscle, extensor digitorum longus muscle, and peroneus longus muscle). A paired samplest-test was conducted to elucidate the statistical significance of spatial-mean conductivities 〈σ^p〉_M1and 〈σ^p〉_M2inM₁andM₂with reference to the conventional extracellular water ratioβ^pby bioelectrical impedance analysis. Significance. From thet-test results, 〈σ^p〉_M1and〈σ^p〉_M2have good correlation withβ^p. In the post-training part, 〈σ^post〉 andβ^postwere significantly higher than in the pre-training part (n = 24,p < 0.001). The relax-pre difference ratios of spatial-mean conductivity Δ〈σ^relax-pre〉 and the relax-pre difference ratios of extracellular water ratio Δβ^relax-prein both MR and CR were lower; on the contrary, the Δ〈σ^relax-pre〉 and Δβ^relax-prein HR were significantly higher than those in post-pre difference ratios of spatial-mean conductivity Δ〈σ^post-pre〉 (n = 8,p < 0.05). The reason for the changes in 〈σ^p〉_M1and 〈σ^p〉_M2are caused by the changes in muscle extracellular volumes. In conclusion,fd-EIT satisfactorily evaluates the effectiveness of human calf muscles under EMS.