Quantification of dermis sodium concentration in skin layers by power spectral density drop of square-wave electrical impedance spectroscopy (PSDd-sEIS)

Abstract

Assessing dermis sodium concentration in skin is essential since an excessive amount of sodium is associated with vascular function disorders. In this research, dermis sodium concentration c has been quantified by the power spectral density drop Δ P of square-wave electrical impedance spectroscopy (PSDd-sEIS). PSDd-sEIS is composed of three stages: (1) dermis voltage measurement, (2) PSDd calculation, and (3) dermis sodium quantification. In the 1st stage, three electrodes are arranged to measure voltage v under the constant current I of square-wave. In the 2nd stage, Δ P is evaluated by the first and third harmonic frequency from v . In the 3rd stage, c is quantified by the developed linear regression. To obtain the highest sensitivity between c and Δ P , four measurement factors (square-wave frequency f sw , duty-cycle γ , electrode distance d, and electrode diameter ø) were optimized using numerical simulations of a skin model. Experiments on multi-layered skin under various c in the range of 5 nM–50 mM were conducted by PSDd-sEIS hardware with optimized measurement factors of f sw ∗ = 100 kHz , γ ∗ = 50 % , d ∗ = 2 mm , and ϕ ∗ = 0.8 mm . As the results, the quantification of c has a good accuracy with the normalized sensitivity ⟨ S ⟩ =0.87 and determination coefficient R2 = 0.92. The measurement factors of f sw and γ affect the power of square-wave excitation to pass through the high resistivity barrier of the stratum corneum, while the measurement factors of d and ø affect the stability of current flow in the dermis.

Sodium concentration imaging in dermis layer by square-wave open electrical impedance tomography (SW-oEIT) with spatial voltage thresholding (SVT)

“…However, the conventional EIT which is based on sinewave injection, has a limitation for imaging the sodium concentration in the dermis layer. The dermis layer is mainly observed at a high frequency, especially above 100 kHz [15], because the stratum corneum as the outer layer has high resistance, which acts as a barrier to low frequency [16,17]. On the other hand, high-frequency measurements increase stray capacitance and common-mode voltages [18], leading to the current injection instability.…”

Free and bound sodium identification by skin dielectric properties separation algorithm of bioelectrical impedance spectroscopy (spa-BIS) in human skin model

“…BIS is applied to obtain the resistivity and relative permittivity of human skin at multiple frequencies [11]. Also, BIS has successfully quantify sodium concentration in dermis layer [12]. The aforementioned studies convey the possibility of measuring sodium-ion concentration in the skin using BIS.…”

Skin layer classification by feedforward neural network in bioelectrical impedance spectroscopy

“…Skin is a multi-layer dielectric medium with different electrical properties related to structural characteristics [ 1 ], chemical composition variations [ 2 ], and different biological functions, in which the assessment of each layer leads to a better understanding of its pathophysiology. As a common modality to measure dielectric characteristics in biological tissue, bioelectrical impedance spectroscopy (BIS) is well-known as low-cost, sensitive to chemical composition, and portable for clinical measurement, which is capable of measuring the electrical conductivity of the human skin layer [ 3 ]. BIS for human skin is utilized to assess skin rubor (or erythema) [ 4 ], skin cancer [ 5 ], diabetes [ 6 ], edema [ 7 ], skin irritation [ 8 ], skin thickness [ 9 ], and drug delivery [ 10 ].…”