Skin capacitance

Loden, M. and Lindberg, M. The influence of a single application of different moisturizers on the skin capacitance. Acta Derm. Venereol. 1991 71 79-82. 

Different types of evidence exist for the clinical efficacy of 10% urea in the treatment of psoriasis (Table 19.1). Early clinical data from a clinical study on various types of hyperkeratosis showed no superior effects on from 10% urea cream compared to ordinary aqueous cream BP in the treatment of psoriasis.10 However, five psoriatic patients with chronic therapy-resistant lesions obtained soft and pliable skin after treatment with 10% urea, but no effect on erythema was observed.17 Psoriatic lesions on the extremities (at least 5 cm in diameter in size) also showed clinical improvement after two weeks of treatment with an ointment containing 10% urea (Basodexan S ointment) in a placebo-controlled study on ten patients.26 Higher values of skin capacitance (suggested to reflect skin hydration) were also noted on urea-treated areas. Increased hygroscopicity and water content were also obtained after treatment with 10% urea ointment in patients with psoriasis vulgaris.27 Moreover, urea treatment reduced epidermal proliferation, measured as an altered expression of involucrin and cytokeratins.26 Treatment of psoriasis vulgaris with 10% urea-formulations support clinical efficacy at evidence-level lb (cf. Figure 19.1). 

Dry senescent skin 60 10 Randomized, double blind, bilateral, placebo controlled Differences in skin capacitance, not clinically 22... 

D. Skin Capacitance and the Use of Direct and Depolarizing Pulsed Currents... 

Modified soap chamber test [20], This is a more elaborate test and is generally used in the case of a major modification of the formulation or use of new ingredients. It involves 25 to 30 panelists. In this test the solutions of the products are applied to panelists under occlusion for two 24-hour periods and visual assessment of erythema and dryness is done by the same techniques as for the exaggerated arm wash test. The instrumental measurement of redness is done after 3 hours of each application and the TEWL measurement is done after 3 hours of first application. The measurement of skin capacitance is done 3 to 5 days after the second application [21]. 

Figure 4.21 shows the dominating effect of sweat duct filling on skin admittance and shows clearly how skin capacitance is in parallel and is therefore unaffected by the parallel conductance change. 

Fig. 2. Variation of skin capacitance values during the treatment period. Changes were doubly evaluated versus basal and control values.

Cutaneous application of a surfactant, such as sodium lauryl sulfate (SLS) or dodecyl sulfate, induces dry, scaly skin (Thune 1996b) with decreased skin capacitance and a dose-dependent increase in TEWL, which is significant by 24 h and maximal by 48-72 h (Di Nardo et al. 1996 Welzel et al. 1996). There are contradictory results concerning the capacity of surfactants to remove epidermal lipids in the same way as solvents do (Thune 1996b Di Nardo et al. 1996), and most studies suggest that they mainly disturb the multilamellar layered lipid structure and facilitate lipid removal, especially after prolonged skin contact (Thune 1996b Kawasaki et al. 1997). Actually, sur-... 

An iontophoretic dosage form for the delivery of insulin would be of little benefit if diabetics could not wear it. Recently, the skin response to a 24-hr iontophoresis dosage form was measured in human volunteers (Maibach, 1994). In terms of comparisons of iontophoretic patches at 200 /A/cm2 and similar patches without current, no significant changes were measured for transepithelial water loss (TEWL), skin capacitance, and skin temperature. The only effect was modest transient erythema. For a 24-hr application, this establishes a well-tolerated current density. In order to determine a well-tolerated total current, we need only know the skin contact area. Experience with passive patches has shown that a total area of SOcm for a system worn all day, every day, may be close to a maximum. Allowing 20 cm2 for si-in adhesion and 30 cm for the anode and cathode, a IS-cm electrode area is estimated. For a current density of 20Q A/cm2, this yields an estimate of 3 mA as well tolerated for a system worn aU day, every day. 

The development in recent years of noninvasive instrumental techniques has considerably increased the level of discrimination between products or surfactants. Significant differences in terms of interaction of products with skin surface are now detected much earlier than clinical signs of irritation. Different test protocols have been described in the literature [86] and have been developed in order to induce no or minimal clinical irritation and compare the effect of siufactants by means of instrumental measurements. Transepidermal water loss (evaporimetry), skin capacitance/conductance (skin surface electrical measurements), and vascular status (laser Doppler flowmetry) measurements seem among the most sensitive bioengineering methods for such a purpose. They assess the effect of the surfactants on alteration of the skin barrier function, skin surface hydration, and microvessels blood flow, respectively. 

Dielectric losses arise from the direct capacitive coupling of the coil and the sample. Areas of high dielectric loss are associated with the presence of axial electric fields, which exist half way along the length of the solenoid, for example. Dielectric losses can be modeled by the circuit given in Figure 2.5.3. The other major noise source arises from the coil itself, in the form of an equivalent series resistance, Rcoii. Exact calculations of noise in solenoidal coils at high frequencies and small diameters are complex, and involve considerations of the proximity and skin depth effects [23],... 

Judd-Hunter color difference scale, 7 321 Juglone, in skin coloring products, 7 847 Juglone derivatives, 21 264-265 Juice softening, 23 463 Junctional heart rhythm, 5 107 Junction capacitance, 22 244 Junction devices, 22 180-181 Junction FETs (JFETs), 22 163, 164. See also Field effect transistors (FETs) physics of, 22 241-245, 249 Junction potentials, 9 582 Junctions, stacking, 23 38-39. See also Josephson junctions p-n junction Just-in-Time technique, 21 172 Jute, 11 287, 288, 292, 293. See also China jute... 

Vascular smooth muscle tone is regulated by adrenoceptors consequently, catecholamines are important in controlling peripheral vascular resistance and venous capacitance. Alpha receptors increase arterial resistance, whereas 2 receptors promote smooth muscle relaxation. There are major differences in receptor types in the various vascular beds (Table 9-4). The skin vessels have predominantly receptors and constrict in the presence of epinephrine and norepinephrine, as do the splanchnic vessels. Vessels in skeletal muscle may constrict or dilate depending on whether ffor 13 receptors are activated. Consequently, the overall effects of a sympathomimetic drug on blood vessels depend on the relative activities of that drug at and 8receptors and the anatomic sites of the vessels affected. In addition, Di receptors promote vasodilation of renal, splanchnic, coronary, cerebral, and perhaps other resistance vessels. Activation of the Di receptors in the renal vasculature may play a major role in the natriuresis induced by pharmacologic administration of dopamine. 

Seidenari, S. and Giusti, G. Objective assessment of the skin of children affected by atopic dermatitis a study of pH, capacitance and TEWL in eczematous and clinically uninvolved skin. Acta. Derm. Venereol. 75, 429-433 (1995). 

Blichmann, C.W., Serup, J., and Winther, A. Effects of single application of a moisturizer evaporation of emulsion water, skin surface temperature, electrical conductance, electrical capacitance, and skin surface (emulsion) lipids. Acta Derm.. Venereol. 1989 69 327-30. 

Pellacani, G., Belletti, B., and Seidenari, S. Evaluation of the short-term effects of skin care products a comparison between capacitance values and echographic parameters of epidermal hydration. Curr. Probl. Dermatol. 1998 26 177-82. 

Eisner, P. and Maibach, H.I., The effect of prolonged drying on transepidermal water loss, capacitance and pH of human vulvar and forearm skin, Acta Derm. Venereol., 70, 105, 1990. 

A 5% urea cream (Canoderm , ACO Hud AB, Sweden) increased skin hydration (measured as capacitance)34 and showed similar efficacy as a 4% urea cream also containing 4% sodium chloride as active ingredient (Fenuril , ACO Hud AB, Sweden) in a double-blind, randomized, and parallel study on 48 atopic patients.35 The clinical and instrumental assessment showed improvements in both groups during the treatment period.35 In another study on atopic dry skin, the 4% urea-formulation... 

Creams containing 3% urea (n = 23) or 10% urea (n = 24) were applied to one of the volar forearms on individuals with some evidence of dry skin for three weeks.38 Both creams improved the skin with respect to dryness characteristics, as evaluated by a dermatologist, measurements of electrical capacitance and conductance, and tape assessments of scaling. Both creams were considered equally effective.38... 

Jemec, G.B. and Serup, J. Epidermal hydration and skin mechanics. The relationship between electrical capacitance and the mechanical properties of human skin in vivo. Acta Derm. Venereol. 1990,70 245-7. 

Eisner, P., Wilhelm, D., and Maibach, H.I., Frictional properties of human forearm and vulvar skin influence of age and correlation with transepidermal water loss and capacitance, Dermatologica, 1990 181 88-91. 

Loden, M., Olsson, H., Axell, T., and Linde, Y.W., Friction, capacitance and transepidermal water loss (TEWL) in dry atopic and normal skin, Br. J. Dermatol., 1992 126 137-141. 

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