Tatsuma Yamamoto

Electrical properties of the epidermal stratum corneum.

The electrical properties of the epidermal stratum corneum were investigated by cellulose adhesive tape stripping. The distribution function of the relaxation times on the impedance locus of stratum corneum was deduced. It was found that this function of the thin layer does not satisfy the Cole-Cole circular arc, but the skin impedance remaining after some strippings compares favourably with the Cole-Cole circular arc. The various dispersions appearing in the skin impedance can be separated and evaluated. The average resistivity and dielectric constant of the stratum corneum and deeper tissues were determined. The direct current resitivity σ of the stratum corneum can be mathematically expressed by the exponential law ρ=ρo -αx where x is the distance from the skin surface. The maximum resistivity ρo on the outermost surface of the stratum corneum and the attenuation coefficient α are evaluated.

Non-linear electrical properties of skin in the low frequency range

This paper describes the non-linear electrical properties of the skin during the passage of a sinusoidal current from the standpoint of the constant-current method. The non-linearity occurs in the current dependency of the skin impedance and in Lissajous figures. It exhibits both rapid and slow variations. The concept of a non-linear impedance and its equivalent circuit are introduced for a sinusoidal voltage. With regard to the current dependency of the impedance it can be said that both the starting point and the degree of the dependency vary with frequency and impedance. The nonlinearity is more apparent with a larger current, a lower frequency, and a higher impedance. with an increasing current, the ionic conductance increases and the polarisation admittance decreases. Lissajous figures are formed when the voltage is distorted notably from the sinusoidal wave form. Detailed investigations are undertaken for the elliptic figures, third harmonics, rectification, and breakdown of the skin appearing with a decrease of the frequency and increase of the current. Finally, the special mechanism of the ionic conduction in the keratin layer is indicated as one of the causes for non-linearity.

Characteristics of skin admittance for dry electrodes and the measurement of skin moisturisation

The properties of skin adminttance were investigated with the intention of applying them to skin moisturisation measurement. Skin admittance is determined by measuring relative permittivity and the resistivity of the stratum corneum, and by contact ratio between dry electrode and stratum corneum. It was found, however, that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin. To measure skin admittance, the following conditions were found to be approriate: (a) frequency of about 100 kHz; (b) concentric electrodes, the diameter of the measuring (inner) electrode being about 5 mm, and (c) an electrode pressure of about 100 g cm−2. Based on these optimal conditions, a system for measuring skin admittance was constructed. All measuring procedures were automated. Experimental observations made with this system have indicated its usefulness for the measurement of skin moisturisation.

Fundamental characteristics of human limb electrical impedance for biodynamic analysis

The paper describes the use of human-limb impedance for biodynamic analysis. The change of human-limb impedance during movement was measured, and was found to be related to kinematic and kinetic parameters. Strong relationships were found between the velocity of change of the forearm impedance and the angular velocity of the elbow joint (correlation coefficient r=−0·97), between the change of foream impedance and the acceleration of a human limb (r=0·86), and between the change of forearm impedance and the velocity of a human limb (r=0·79). A change of upper-limb impedance was caused by a change in a sectional area of muscular tissue in the measured part and a change of blood volume during movement of an upper limb. In tennis, there was a strong relationship between a change of forearm impedance and ball velocity (r=0·87). Impedance waveforms were useful for analysis of the movement pattern and the stability of movement in tennis. This method has the following characteristics: (a) it does not have a spatial and temporal limitation for measurement; (b) the subject is scarcely restricted in movement; (c) the data processing can be handled easily and quickly; (d) impedance waveforms inherently show magnitude, form and stability of movement.

Dispersion and correlation of the parameters for skin impedance

] I n t r o d u c t i o n IT is well known that the skin impedance undergoes dispersion due to various factors inside and outside the body. A few precise analyses of the dispersion of the skin impedance have been carried out in the past, but only ALMASI and Scm~lxr (1970) reported on the dispersion of the absolute value of the impedance at 10 Hz. However, the skin impedance can be expressed with an equivalent circuit as reported in a previous paper (YAMAMOTO and YAMAMOTO, 1977), and this necessitated the three independent parameters for a perfect description: Accordingly, dispersion and correlation of these parameters are described.

Dynamic system for the measurement of electrical skin impedance.

MEASUREMENT of the skin impedance is difficult because of its time dependency, random variation, nonreproducibility and nonlinearity. Taking these characteristics into consideration, the authors designed a dynamic system which employs a time-multiplex scheme and utilises a synchronous rectifier to measure the resistive and reactive components of the skin impedance. Since the system allows continuous impedance recordings for one point on the skin simultaneously at N different frequencies, it is possible to obtain rapidly the frequency characteristics of time varying impedance. Since the system allows continuous impedance recordings simultaneously for N points at one frequency, it is also possible to compare the impedances at different points with each other. This system can be realised in the form of a very lowcost device.

Measurement of electrical bio-impedance and its applications

This paper describes: 1) the measurement method of electrical bio-impedance; 2) presentations of models of bio-impedance and their applications to some impedance analyses; 3) the analyses of steady state and dynamical state of electrical properties of the skin; and 4) the applications of bio-impedance. The applications include: 1) the influence of skin impedance to biological potential measurement; 2) skin moisturization measurement using skin admittance; and 3) gait analysis using lower leg electrical impedance.

Application of mechanical mobility of periodontal tissues to tooth mobility examination.

Tooth mobility examination is important in planning dental treatment, as it may give an indication of alveolar bone loss and the condition of the periodontal ligament. In clinical dental diagnosis a manual tooth mobility examination is useful. However, its determination of tooth mobility is subjective and depends on the skill and experience of the clinician. The authors have previously reported on a device for measuring the biomechanical properties of human periodontium using an impedance head. Using this device, the mechanical mobility of periodontium can be measured and the mechanical parameters of the periodontal physical model are obtained. Tooth mobility is defined objectively on the basis of discriminant scores of mechanical parameters, and a mobility triangle (MT) figure is drawn as a record for visual interpretation. The paper describes the validation of the mechanical mobility measurements and their interpretation using mobility parameters and a personal computer to produce a mobility triangle figure. The method is compared favourably with clinical mobility measurement. The relationship of the model to underlying pathology is tested by measurements performed on various tooth model systems.

Measurement of low-resistance points on the skin by dry roller electrodes

Dry skin resistance is measured by application of a positive direct current flowing from a dry electrode to the skin. A device for finding low-resistance points is proposed, and methods for measuring the distribution of skin resistance are discussed. The voltage ratio is used to find the low-resistance points, using both a constant-current and a constant-voltage method. The latter is shown to be particularly effective. Guidelines for optimal design of the device are proposed.<<ETX>>

Formative Mechanisms of Current Concentration and Breakdown Phenomena Dependent on Direct Current Flow Through the Skin by a Dry Electrode

Direct current flow into the skin by dry electrode is useful in the fields of the electrocutaneous stimulation in sensory substitution systems and the probing of acupuncture points by means of electric resistance. During such. use, both the occurrences of a pain sensation and the electric breakdown of the skin become a hindrance to application. Equations describing these phenomena have been derived and the formative mechanisms of three phenomena, namely the current concentration in a minutely localized region, the occurrence of pain sensation as a result of heat generation, and the electric breakdown of the skin, have been made clear. The impottant values from which the key to solutions for these problems can be concretely obtained using equations are discussed in detail.