On assessment of skin reactivity using electrical impedance.

Pathophysiological events in biological tissue are characterized by a shift in electrical impedance spectra of the tissue under study. In this paper, techniques based on electrical impedance are reviewed with emphasis on their possible role in evaluating the skin reactivity of an individual, including results from impedance measurement studies on patients with allergic contact reactions, wheals, tuberculin tests, and irritant contact reactions and on an appropriate number of controls. The results show that, compared to relevant controls, at different types of experimental cutaneous reactions, both of allergic and irritant type, statistically significant changes of the impedance parameters have been detected. Each reaction type had a specific impedance index pattern. Data up to now indicate that the improved impedance technique offers not only a noninvasive alternative for characterization and perhaps differentiation between the skin responses induced by either an allergen or an irritant, but also a capability to distinguish responses induced by chemically different irritants.

Electrical impedance for quantification and classification of experimental skin reactions.

BACKGROUND: Pathophysiologic events in biological tissue are characterized by a shift of the electrical impedance spectra of the tissue under study. OBJECTIVE: To discuss studies on experimental skin reactions with an improved impedance spectrometer. The instrumentation is related to noninvasive techniques based on other physical principles. METHODS: The results from studies on patients with allergic contact reactions (n = 8), prick tests (n = 10), and irritant contact reactions (benzalkonium chloride [n = 14], sodium lauryl sulfate [n = 12], and nonanoic acid [n = 14]), and an appropriate number of controls are reviewed. RESULTS: Results show statistically significant changes of the impedance parameters when compared with relevant controls, at different types of experimental cutaneous reactions, both allergic and irritant type. Each reaction type had a specific impedance index pattern. CONCLUSIONS: Current data indicate that the improved impedance technique offers a possible noninvasive alternative for characterization and perhaps differentiation, not only between the skin responses induced by either an allergen or an irritant, but also a capability to distinguish responses induced by chemically different irritants. The assumption that the impedance method is capable to distinguish allergic from irritant contact reactions has not been proven yet in direct comparative studies.

Do urea and sodium chloride together increase the efficacy of moisturisers for atopic dermatitis Skin? A comparative, double-blind and randomised study.

Urea has long been used to treat dry skin. In the present report, we compared two creams, identical with the exception that one contained both urea and sodium chloride and the other urea alone, in 22 patients with atopic dermatitis. Following a 2-week wash-out period, their clinically non-eczematous, rough or normal-appearing skin on the forearms was treated twice daily in a double-blind and randomised manner. We examined the treated areas by measuring transepidermal water loss, capacitance and electrical impedance. Our findings suggest that a moisturiser containing both urea and sodium chloride seems somewhat more effective than the same moisturiser without sodium chloride, at least concerning the ability to reverse impedance indices of atopic skin towards normal, an effect ascribed mainly to changes in hydration of the stratum corneum. However, the clinical significance of our impedance measurements is somewhat premature to decide.

Instrumental measurement of the Mantoux test: differential effects of tuberculin and sodium lauryl sulphate on impedance response patterns in human skin.

BACKGROUND AND OBJECTIVE: The tuberculin (PPD) test is a model reaction for the cell-mediated immune system of the skin. The aim of this study is to compare the non-invasive technique based on electrical impedance for investigation of the tuberculin test with an irritant contact reaction induced by sodium lauryl sulphate, which has already been carefully evaluated using this method. METHODS: 0.1 ml of PPD (2 TU) was injected intracutaneously into the volar forearms of 20 adult healthy subjects, all known to be tuberculin sensitized. Assessments were performed 3 and 7 days after the injections, using visual scoring, a new electrical impedance technique and transepidermal water loss (TEWL). RESULTS: In the 16 cases that completed the study, compared to relevant controls and reactions induced by sodium lauryl sulphate statistically significant changes in 3 of the 4 impedance indices were found: both the means of index MIX and index IMIX increased (p< or = 0.01) and the mean of index PIX decreased (p< or = 0.05). Furthermore, similar impedance response patterns occurred in another cell- mediated immune reaction that we have studied previously - namely, the allergic contact reaction induced by nickel sulphate. Unlike the irritant reactions, no significant increase in TEWL values in tuberculin reactions were found. This can be explained by the fact that the epidermis is little affected, since the inflammatory process in the tuberculin reaction is located more deeply in the dermis than with the irritant reaction. CONCLUSION: The current study strongly indicates that electrical impedance in the described version, besides contact dermatitis, also seems suitable for studies of the tuberculin reaction. This will add a new indication for the technique, and studies of further clinical applications are in progress.

An electrical impedance technique for assessment of wheals.

In previous studies of the electrical impedance of the skin, we introduced a set of physical indices which could be used to distinguish between the cutaneous effects produced by different irritants and allergic contact reactions. In this study, wheals were induced in 10 allergic patients by performing prick tests on the forearm with the relevant allergen and histamine, respectively. Normal skin was used for control. The wheals were evaluated by visual scoring, laser Doppler, and electrical impedance. As expected, there was a close agreement between the visual and laser Doppler readings. Compared to the controls, there were significant changes in the electrical impedance of the wheals, especially in the index related to the phase angle. The changes in the indices were found to follow a particular pattern, which diverged from those obtained in contact skin reactions of both allergic and irritant type. Our results indicate that, by the application of the impedance technique, it will be possible to characterize objectively and quantify the wheal reaction. The results also suggest that cutaneous reactions of completely different causes, such as allergic skin reactions of the late and immediate type, and irritant contact reactions, may be distinguished on the basis of their effects on the electrical impedance of the skin.

Electrical impedance compared with other non-invasive bioengineering techniques and visual scoring for detection of irritation in human skin.

A new, non-invasive device, which enables local measurements of electrical impedance to a controlled depth, has been used to evaluate the degree of irritation in human skin. The results have been compared with those obtained using other non-invasive techniques, i.e. with transepidermal water loss (TEWL), electrical capacitance moist measurement (ECM), laser-Doppler flowmetry (LDF), and visual scoring. Sodium lauryl sulphate solutions (0.1-5.0%), and a blank, were applied in Finn Chambers for 24 h on the volar forearm of 10 healthy volunteers. Values were recorded before application of the test chambers, and at 1 h, 24 h, 1 week and 2 weeks after removal. Thus, both the degree of initial damage and the healing process were monitored. There was close agreement among values obtained using electrical impedance, TEWL and visual readings. Results obtained using ECM and LDF were not consistent with the other three methods. In evaluating irritation of the skin, the practical situation may influence the choice of bioengineering tools. In most circumstances, a combination of methods would be preferable.

Baseline electrical impedance measurements at various skin sites - related to age and sex.

BACKGROUND/AIMS: During previous studies on the electrical impedance of the skin, we formulated a set of four physical indices that could be used to distinguish between the cutaneous effects produced by different chemical irritants. We now employ the electrical impedance technique to compare the properties of different anatomical areas of the skin, using the same set of indices. METHODS: Investigations were performed on 131 healthy volunteers, who were divided into four groups on the basis of age and sex. Readings of electrical impedance were taken from ten different regions over the body, and transepidermal water loss was measured for comparison. RESULTS: Baseline values of electrical impedance of the skin were shown to vary, depending on the site. Age was also found to exert a major influence, causing an increase in the indices related to magnitude (MIX, RIX, and IMIX) with increasing age, and a decrease in that related to phase (PIX), while sex had only a marginal effect. CONCLUSIONS: As with other non-invasive techniques, baseline characteristics differ from place to place over the body surface, and age is another important determining factor.