Electrical Skin Impedance Research Articles

Numerical sensitivity modeling for the detection of skin tumors by using tetrapolar probe

The measurement of electrical impedance of skin using surface electrodes permits the assessment of changes in local properties of the skin and can be used in the detection of tumors. The sensitivity of this technique depends mainly on the geometry of the probe and the size of the tumor. In this article, the impedance method was used to estimate the sensitivity of a tetrapolar probe in detecting small regions of increased conductivity in a stratified model of human skin. The impedance method was used to model the potential distribution using fasorial analysis to solve the node equations of the equivalent circuit. Interpolation was applied to reduce discretization error. The skin was modeled as a three-layer structure with different conductivity and permittivity obtained from the literature. A tumor was modeled as a small volume with admittivity four times higher than the normal tissue. Sensitivity calculation was made as a function of electrode diameter and separation, tumor size, and excitation frequency. The simulations indicated that by inserting a one square millimeter tumor in the epidermis, the load impedance to the current source varies about 1% while the transfer impedance varied 8%. The sensitivity also increases nonlinearly with increasing tumor area and thickness. Additionally, it was found that the sensitivity of the transfer impedance has a maximum value when the electrodes are separated by 1.8 mm. The results show that transfer impedance measurements of the skin may detect small skin tumors with a reasonable sensitivity by using an appropriate tetrapolar probe.

Effect of ceramide acyl chain length on skin permeability and thermotropic phase behavior of model stratum corneum lipid membranes

Stratum corneum ceramides play an essential role in the barrier properties of skin. However, their structure–activity relationships are poorly understood. We investigated the effects of acyl chain length in the non-hydroxy acyl sphingosine type (NS) ceramides on the skin permeability and their thermotropic phase behavior. Neither the long- to medium-chain ceramides (8–24C) nor free sphingosine produced any changes of the skin barrier function. In contrast, the short-chain ceramides decreased skin electrical impedance and increased skin permeability for two marker drugs, theophylline and indomethacin, with maxima in the 4–6C acyl ceramides. The thermotropic phase behavior of pure ceramides and model stratum corneum lipid membranes composed of ceramide/lignoceric acid/cholesterol/cholesterol sulfate was studied by differential scanning calorimetry and infrared spectroscopy. Differences in thermotropic phase behavior of these lipids were found: those ceramides that had the greatest impact on the skin barrier properties displayed the lowest phase transitions and formed the least dense model stratum corneum lipid membranes at 32 °C. In conclusion, the long hydrophobic chains in the NS-type ceramides are essential for maintaining the skin barrier function. However, this ability is not shared by their short-chain counterparts despite their having the same polar head structure and hydrogen bonding ability.

Electrical Impedance of Acupuncture Meridians: The Relevance of Subcutaneous Collagenous Bands

BackgroundThe scientific basis for acupuncture meridians is unknown. Past studies have suggested that acupuncture meridians are physiologically characterized by low electrical impedance and anatomically associated with connective tissue planes. We are interested in seeing whether acupuncture meridians are associated with lower electrical impedance and whether ultrasound-derived measures – specifically echogenic collagenous bands - can account for these impedance differences.Methods/ResultsIn 28 healthy subjects, we assessed electrical impedance of skin and underlying subcutaneous connective tissue using a four needle-electrode approach. The impedances were obtained at 10 kHz and 100 kHz frequencies and at three body sites - upper arm (Large Intestine meridian), thigh (Liver), and lower leg (Bladder). Meridian locations were determined by acupuncturists. Ultrasound images were obtained to characterize the anatomical features at each measured site. We found significantly reduced electrical impedance at the Large Intestine meridian compared to adjacent control for both frequencies. No significant decrease in impedance was found at the Liver or Bladder meridian. Greater subcutaneous echogenic densities were significantly associated with reduced impedances in both within-site (meridian vs. adjacent control) and between-site (arm vs. thigh vs. lower leg) analyses. This relationship remained significant in multivariable analyses which also accounted for gender, needle penetration depth, subcutaneous layer thickness, and other ultrasound-derived measures.Conclusion/SignificanceCollagenous bands, represented by increased ultrasound echogenicity, are significantly associated with lower electrical impedance and may account for reduced impedances previously reported at acupuncture meridians. This finding may provide important insights into the nature of acupuncture meridians and the relevance of collagen in bioelectrical measurements.

Características de la resistencia eléctrica de la piel en los puntos de acupuntura de humanos sanos

The aim of this study was to evaluate the phenomenon of electrical skin resistance (ESR) changes at different acupuncture points (APs). This single-blinded study was performed at the hospital of the University of Munich. Six common APs were measured (TE5, PC6, LU6, ST36, SP6, GB39) in 53 subjects. Subgroups were formed with varying time intervals for follow-ups (1 minute, 1 hour, 1 week) and a varying grade of reduction of the stratum corneum. Electrical skin resistance measurements (ESRMs) were taken from a skin area of 6 × 6 cm using an array consisting of 64 (8 × 8) electrodes. The electrodes corresponding to the AP were located and the ESRM results were compared to those of the surrounding electrodes. The methodological setting made it possible to minimize major influence factors on electrical skin impedance measurements. A total of 631 ESRMs was evaluated: In 62.8% of the measured APs, no significant ESR difference was found. In 234 (37.2%) of the ESRMs, the ESR at the AP was significantly different from the surrounding skin area, with 163 (25.9%) points showing a lower and 71 (11.3%) points showing a higher ESR. Reproducibility was extremely high after 1 minute but was low after 1 hour and 1 week. This study shows that electrical skin resistance at APs can either be lower or higher compared to the surrounding area. The phenomenon is characterized by high short-term and low long-term reproducibility. Therefore, we conclude that APs might possess specific transient electrical properties. However, as the majority of the measured APs did not show a changed ESR, it cannot be concluded from our data that electrical skin resistance measurements can be used for acupuncture point localization or diagnostic/therapeutic purposes.

Prospective study comparing skin impedance with EEG parameters during the induction of anaesthesia with fentanyl and etomidate

ObjectiveSympathetic stimulation leads to a change in electrical skin impedance. So far it is unclear whether this effect can be used to measure the effects of anaesthetics during general anaesthesia. The aim of this prospective study is to determine the electrical skin impedance during induction of anaesthesia for coronary artery bypass surgery with fentanyl and etomidate.MethodsThe electrical skin impedance was measured with the help of an electro-sympathicograph (ESG). In 47 patients scheduled for elective cardiac surgery, anaesthesia was induced with intravenous fentanyl 10 μg/kg and etomidate 0.3 mg/kg. During induction, the ESG (Electrosympathicograph), BIS (Bispectral IndeX), BP (arterial blood pressure) and HR (heart rate) values of each patient were recorded every 20 seconds. The observation period from administration of fentanyl to intubation for surgery lasted 4 min.ResultsThe ESG recorded significant changes in the electrical skin impedance after administration of fentanyl and etomidate(p < 0.05). During induction of anaesthesia, significant changes of BIS, HR and blood pressure were observed as well (p < 0.05).ConclusionsThe electrical skin impedance measurement may be used to monitor the effects of anesthetics during general anaesthesia.

Biomedical engineering meets acupuncture - development of a miniaturized 48-channel skin impedance measurement system for needle and laser acupuncture

BackgroundDue to controversially discussed results in scientific literature concerning changes of electrical skin impedance before and during acupuncture a new measurement system has been developed.MethodsThe prototype measures and analyzes the electrical skin impedance computer-based and simultaneously in 48 channels within a 2.5×3.5 cm matrix. Preliminary measurements in one person were performed using metal needle and violet laser (405 nm) acupuncture at the acupoint Kongzui (LU6). The new system is an improvement on devices previously developed by other researchers for this purpose.ResultsSkin impedance in the immediate surroundings of the acupoint was lowered reproducibly following needle stimulation and also violet laser stimulation.ConclusionsA new instrumentation for skin impedance measurements is presented. The following hypotheses suggested by our results will have to be tested in further studies: Needle acupuncture causes significant, specific local changes of electrical skin impedance parameters. Optical stimulation (violet laser) at an acupoint causes direct electrical biosignal changes.

Skin impedance correlates to sedation grade, plasma propofol concentrations and bispectral index during a target-controlled infusion of propofol

Sympathetic activity, measured as changes in electrical skin impedance, may be used to assess the adequacy of general anaesthesia. The aim of this prospective study was to evaluate electrical skin impedance in comparison with bispectral index values and the Observer's Assessment of Alertness and Sedation (OAAS) scale during propofol infusion. Electrical skin impedance was measured with an electrosympathicograph. In 22 patients and eight healthy volunteers, anaesthesia was induced and maintained with propofol that was administered via a target-controlled infusion pump at increasing plasma concentrations. Bispectral index, electrosympathicograph and OAAS values were compared at six successive predicted target plasma concentrations (T 1-6: 0, 1.3, 1.7, 2.0, 2.4 and 2.8 microg ml(-1)). The changes in the electrical skin impedance measured with the assistance of the electrosympathicograph correlated with the changes in bispectral index values at each measurement time point and during the whole course (P < 0.0001), with the target plasma propofol concentrations (P < 0.0001), and with the OAAS scale (P < 0.0001). The observed correlations between electrical skin impedance, predicted plasma concentrations of propofol and OAAS scale appear to justify further investigation of skin impedance as a depth of anaesthesia monitor.

Recovery of Skin Barrier Properties after Sonication in Human Subjects

The SonoPrep® ultrasonic skin permeation system is used clinically to increase skin permeability for rapid, noninvasive delivery of local anaesthetics. This study tested the hypothesis that sonication can generate a long-lived increase of skin permeability for continuous transdermal drug delivery and diagnostic metabolite extraction. To accomplish this, the volar forearm skin of ten healthy adult subjects was sonicated. As a surrogate measure of skin permeability, skin electrical impedance was measured at occluded and nonoccluded sites every hour over a period of 48 h. Sonication dramatically increased skin permeability, as demonstrated by a large drop in skin impedance. Under occlusion, sonicated skin remained highly permeable during the entire 42-h period of occlusion, which was followed by an immediate decrease in permeability upon removal of occlusion. Without occlusion, sonicated skin retained elevated permeability throughout the 48-h experiment, but regained its barrier function more quickly. Therefore, sonication can increase skin permeability for prolonged periods of time, especially under the effect of occlusion, and has potential to facilitate continuous transdermal drug delivery and diagnostic metabolite extraction. (E-mail: prausnitz@gatech.edu)

Characteristics of Electrical Skin Resistance at Acupuncture Points in Healthy Humans

The aim of this study was to evaluate the phenomenon of electrical skin resistance (ESR) changes at different acupuncture points (APs). This single-blinded study was performed at the hospital of the University of Munich. Six common APs were measured (TE5, PC6, LU6, ST36, SP6, GB39) in 53 subjects. Subgroups were formed with varying time intervals for follow-ups (1 minute, 1 hour, 1 week) and a varying grade of reduction of the stratum corneum. Electrical skin resistance measurements (ESRMs) were taken from a skin area of 6 x 6 cm using an array consisting of 64 (8 x 8) electrodes. The electrodes corresponding to the AP were located and the ESRM results were compared to those of the surrounding electrodes. The methodological setting made it possible to minimize major influence factors on electrical skin impedance measurements. A total of 631 ESRMs was evaluated: In 62.8% of the measured APs, no significant ESR difference was found. In 234 (37.2%) of the ESRMs, the ESR at the AP was significantly different from the surrounding skin area, with 163 (25.9%) points showing a lower and 71 (11.3%) points showing a higher ESR. Reproducibility was extremely high after 1 minute but was low after 1 hour and 1 week. This study shows that electrical skin resistance at APs can either be lower or higher compared to the surrounding area. The phenomenon is characterized by high short-term and low long-term reproducibility. Therefore, we conclude that APs might possess specific transient electrical properties. However, as the majority of the measured APs did not show a changed ESR, it cannot be concluded from our data that electrical skin resistance measurements can be used for acupuncture point localization or diagnostic/therapeutic purposes.

Diagnosing Diseases by Measurement of Electrical Skin Impedance

Recently, we have seen the development of diagnostic tools based on the rationale that the measurement of electrical impedance of specific dermal zones might reflect the occurrence of pathological states in corresponding internal organs. Studies published lately have shown the diagnostic potential of this technique. We set out to evaluate the accuracy of this tool in diagnosing cancer. Our study group was composed of cancer patients visiting the Oncology clinic for a routine follow-up. All patients underwent conventional medical history and physical examination by a physician. We evaluated a device manufactured by Medex Screen Ltd. The device analysis was carried out by a physician who was blinded to the previous diagnosis. A third researcher compared the "conventional" diagnosis with the Medex device output using standard statistical analysis. Overall, 125 cancer patients were included in the study. When comparing Medex Screen diagnostic technique with the conventional methods of diagnosis for the various disorders we found a sensitivity of 76.2%, 78.7%, and 92.9% and a specificity of 95.0%, 90.7%, and 90.4% for lung, breast, and prostate cancer, respectively. Existence of metastatic disease or specific treatment did not affect the diagnostic properties of the described device. Although the exact mechanism is not entirely clear, measurement of electrical impedance of dermal-visceral zones has the potential to serve as a diagnostic and perhaps a screening tool for neoplastic pathologies. Further research should be conducted to create more evidence to support or dispute the use of this technique as a reliable diagnostic tool.

Electrical Skin Impedance at Acupuncture Points

To test whether electrical skin impedance at each of three acupuncture points (APs) is significantly lower than at nearby sites on the meridian (MP) and off the meridian (NP). Two instruments - Prognos (MedPrevent GmbH, Waldershof, Germany), a constant-current (DC) device, and PT Probe (designed for this study), a 100-Hz sinusoidal-current (AC) device-were used to record electrical impedance at three APs (right Gallbladder 14, right Pericardium 8, and left Triple Energizer 1), and two control sites for each AP. Each AP, MP, and NP was measured four times in random order with each device. The study was conducted over a period of 4 days at the Oregon College of Oriental Medicine (OCOM). Twenty (20) healthy adults (14 women and 6 men), all recruited from the OCOM student body and faculty, participated in the study. The Prognos measurements had an intraclass correlation (ICC) = 0.84 and coefficient of variation (CV) = 0.43. The PT Probe had ICC = 0.81 and CV = 0.31. Impedance values at APs were not significantly less than at MPs or NPs. Impedance values at MPs were also not significantly less than NPs, although their individual p values were <0.05 in 4 of 6 cases. There was a significant trend of increasing impedance with repeated measurements with both the Prognos (p =0.003) and the PT Probe (p= 0.003). Within the reliability limits of our study methods, none of the three APs tested has lower skin impedance than at either of the nearby control points. These results are not consistent with previous studies that detected lower skin impedance at APs than nearby sites. Further study is necessary to determine whether MPs have lower skin impedance than nearby NPs. Our study suggests caution is warranted when developing, using, and interpreting results from electrodermal screening devices. Further studies are needed to clarify the clinically important and controversial hypothesis that APs are sites of lower impedance.

Measurement of Electrical Skin Impedance of Dermal-Visceral Zones as a Diagnostic Tool for Disorders of the Immune System

Among complementary medicine approaches, diagnostic screening tools based on neuroreflexology have been recently developed. Such techniques are based on the rationale that measurement of electrical impedance of specific dermal zones might reflect the occurrence of pathological states in the corresponding internal organs or systems. Our objective was to evaluate the reliability of a neuroreflexology-based diagnostic test in diagnosing immune-mediated diseases in a blinded single centre study. Seventy-eight patients with immune-mediated diseases (38 patients with autoimmune diseases (AD), and 40 allergic patients) were included in the study. Thirty age and sex matched healthy subjects were also evaluated as a control group. All the patients and subjects underwent conventional medical history and physical examination. We evaluated a device manufactured by Medex Screen Ltd (Arad, Israel). The Medex Test analysis was carried out by a second physician who was blinded to the previous diagnosis. A high correlation between the formal clinical diagnosis and the results of the measurement of electrical skin impedance was reported, with a specificity of 93.3% and a sensitivity of 81.2%. Both sensitivity and specificity dropped when analysing the autoimmune and the allergic group separately, but remained significant for the autoimmune diseases. Degree of activity of the allergic disorders, or specific treatment, did not affect the diagnostic properties of the described device. The Medex Test neurophysiology based technique has the potential to serve as a diagnostic tool for immune based pathologies. Future studies will define this tool place in routine evaluation and potential screening ability.

Biophysical assessment of atopic dermatitis skin and effects of a moisturizer

The mechanisms of the skin barrier impairment in patients with atopic dermatitis (AD) are still unknown and need further studying. We evaluated the skin of healthy subjects and of patients having atopic dermatitis with an instrument measuring electrical impedance and other noninvasive methods (transepidermal water loss, capacitance) and studied the effects of a new emollient [Proderm (Pro-Q in the USA)]. After a 2-week washout period, we treated clinically noneczematous skin on the forearm of 24 patients with AD and assessed the effects with the noninvasive methods. 22 healthy subjects were used as controls. The findings indicate that barrier function and hydration, and certain patterns of electrical impedance of AD skin are abnormal compared with normal skin. Moreover, there was an increase in hydration in patients' skin after treatment and a reversal of certain impedance indices towards normal. Our findings demonstrate that the moisturizer we used changes some biophysical parameters when applied to atopic skin. In addition, a technique based on electrical impedance seems to give valuable information in atopic skin studies, especially the effects of moisturizers.

Relationships between skin's electrical impedance and permeability in the presence of chemical enhancers

Stratum corneum, the outermost layer of the skin, offers a strong barrier to the movement of solutes as well as ions. We report on the existence of a relationship between skin's electrical impedance and its permeability to hydrophilic (mannitol and inulin) as well as hydrophobic (corticosterone and estradiol) solutes in the presence of 33 distinct chemical penetration enhancer formulations. The correlation between impedance and permeability was excellent (r2=0.8) for hydrophilic solutes and moderate, yet significant (r2∼0.5), for hydrophobic solutes. The possibility of using skin's electrical impedance to choose potent formulations was quantitatively assessed. Percentile ranking of penetration enhancers based on their effect on skin's electrical impedance matched well with the ranking based on their effect on solute permeability (r2>0.9 for both mannitol and estradiol). These studies demonstrate the feasibility of using skin’s electrical impedance to screen potent chemical enhancers.

Measuring depth depends on frequency in electrical skin impedance measurements

Background/aims: Multi‐frequency electrical measurements in vivo on stratum corneum are frequently reported in the literature. It is well known that the measured volume of skin is dependent on measuring frequency, and we wanted to investigate to what extent viable skin influences the measured impedance as a function of frequency.Methods: Finite element modelling (FEM) was used to investigate the current and potential distribution in the skin when measuring impedance with two concentric surface electrodes.Results: The study showed that the impedance measured reflects mainly the stratum corneum at low frequencies, in this case below 1 kHz, and that the viable skin dominates at higher frequencies.Conclusion: It is concluded that a multi‐frequency measurement on isolated stratum corneum is not possible in vivo with conventional techniques, except within a very narrow and low frequency range.

A model for human skin impedance during surface functional neuromuscular stimulation.

A new mathematical model for the bulk electrical impedance of human skin is presented. In particular this model describes the impedance of skin during surface functional neuromuscular stimulation (FNS) with square stimulation pulses. Experimental data are presented that illustrate the nonlinear dynamic properties of human skin during current and voltage controlled stimulation. Model predictions are compared to experimental data, measured under both constant voltage and constant current transcutaneous stimulation. It is found that this model captures a variety of nonlinear time-varying effects observed in the skin impedance when stimulating with either protocol. This model may be used as part of large neuromusculoskeletal models or in the more accurate modeling of transcutaneous FNS, which is currently the most common clinical implementation of FNS.

Inter- and Intra-Individual Differences in Human Stratum Corneum Lipid Content Related to Physical Parameters of Skin Barrier Function In Vivo

For a full understanding of the properties of the human skin barrier, physical macroscopic parameters of barrier function must be correlated to the structural organization of the barrier on a molecular level. This study was undertaken to relate differences in the relative composition of the three main lipid classes of human stratum corneum, i.e., free fatty acids, cholesterol, and ceramides, to differences in transepidermal water loss, stratum corneum electrical impedance, and corneometer value. A new high performance liquid chromatography/light scattering detection-based analysis method recently developed was used for collection of quantitative lipid data in conjunction with gas chromatography/mass spectrometry/flame ionization detection measurements on the free fatty acid fraction. After subtraction of contaminating lipid fractions we have estimated the molar ratio of the human skin barrier lipid composition to be, respectively, 15% cholesterol esters, 16% saturated long chain free fatty acids, 32% cholesterol, and 37% ceramides. The inter-individual difference in the relative amount of free fatty acids, cholesterol, and ceramides, respectively, can be >100% in the individual case. It was found that the relative amount of ceramides to cholesterol is larger in the wrist area, paralleled by a higher transepidermal water loss and corneometer value as well as different skin electrical impedance values as compared with the upper forearm area. We conclude that the site-dependent differences in the stratum corneum lipid composition are small compared with the large inter-individual variation. Interestingly, in the individual case, no correlation was registered between relative ceramide content and barrier properties.

Contrast media extravasation during dynamic CT: detection with an extravasation detection accessory.

To detect extravasation of contrast media during mechanical power injection at dynamic computed tomography, a 5 x 8-cm pliable adhesive patch was applied to the skin over the intravenous cannula and connected to the power injector with a cable to monitor electrical skin impedance. If the rate of change or the slope of impedance over time indicated an extravasation event, the power injector was set into a pause mode. In animal and human studies, monitoring with the device was successful. Extravasation of ionic contrast agents decreased impedance and that of nonionic agents increased impedance.

Mathematical Modeling as a Tool for Basic Research in Acupuncture

We propose and illustrate a five-step strategy for basic research of traditional explanatory frameworks of acupuncture. Our approach is based on using mathematical models as a bridge between the traditional explanatory frameworks of acupuncture and Western research technologies. Step 1. Carefully select and document case studies that would allow simultaneous interpretation within several "traditional" explanatory frameworks of acupuncture. Step 2. Develop minimal theoretical models connecting the diagnosis and treatment within the context of each of the selected explanatory frameworks of acupuncture. Step 3. Develop minimal dynamical systems models for each theoretical model from Step 2, so as to tighten their logical structure and to bring them into a falsifiable and more abstracted format (which provides the link between the theoretical models at Step 2 and possible Western-based models, and hence Western measurement technology). Step 4. Interpret the mathematical models from Step 3 within the framework of "Western" scientific perspectives. Step 5. Select and conduct appropriate "objective" (skin electrical impedance, etc.) measurements to test the validity of the models at Step 4. Repeat Steps 1-5 as needed.

Effect of current, ionic strength and temperature on the electrical properties of skin

The complex electrical impedance of hairless mouse skin was measured as a function of frequency, and resistance and capacitance were determined. Increasing the ionic strength of the bathing medium, and increasing the magnitude of current, decreased resistance, whereas capacitance was, in general, unchanged. These changes occurred rapidly. The decrease in resistance with increasing the ionic strength of the bathing medium was consistent with elevated ion levels within the ion-conducting pathways of the membrane. The decrease in resistance by increasing the magnitude of current seems to be related to alteration of the current-conducting pathway. With increasing temperature, resistance also decreased while capacitance increased. The activation energy for ion conduction through the skin was estimated to be 3.4 kcal/mol at physiologically relevant temperatures. The most marked changes occurred at the phase transition temperature (60°C) of the stratum corneum (SC) lipids; resistance fell dramatically and capacitance steadily increased — ultimately, the impedance became independent of frequency, suggesting that the capacitive properties of the barrier had been lost. Overall, the results provide mechanistic insight into ion conduction through the skin and into the role of SC lipids in skin capacitance.