S. Ollmar
Karolinska Institutet, CLINTEC, Emeritus
Il est etabli que le courant de basse frequence est limite a l'espace extracellulaire, tandis que de plus hautes frequences sont transmises par capacite a travers les membranes cellulaires. Un des types d'irritation de la peau est... more
Il est etabli que le courant de basse frequence est limite a l'espace extracellulaire, tandis que de plus hautes frequences sont transmises par capacite a travers les membranes cellulaires. Un des types d'irritation de la peau est l'oedeme extracellulaire. Un index d'impedance, ou index d'irritation, defini comme le quotient du module de l'impedance a 20kHz et de celui a 1MHz, a ete observe etre le plus sensible a des reactions irritatives provoquees par le lauryl-sulfate de sodium (SLS) a des concentrations plus basses que celles produisant une modification visible de la peau. Des spectres d'impedance electrique entre 1kHz et 1MHz ont ete mesures a cinq profondeurs. Les resultats ont ete mis en relation avec l'aspect histologique des differentes couches de la peau. L'observation dominante a ete un epaississement de l'epiderme du a l'œdeme. La plus grande amplitude du signal d'impedance a ete constatee pour une profondeur de mesure comprenant tout l'epiderme. Du point de vue de l'EIT, nos experiences suggerent d'imbiber la peau avec le SLS pour provoquer une legere dermatite avant les mesures. Une telle lesion, faible et reversible, de la peau entraine une amelioration importante des proprietes conductrices de la peau. Cela devrait diminuer les distorsions en EIT dues a l'interface electrode/peau.
Research Interests:
Page 1. PREDICTION OF BIO-IMPEDANCE PROPERTIES OF CHEMICALLY INDUCED SKIN IRRITATIONS Peter Åberg a , Ingrid Nicander b , Paul Geladi c ,Stig Ollmar a a Karolinska Institutet, Medical Engineering, Novum ...
Our aim is to establish an objective, easy-to-use technique to evaluate tissue irritation in vivo using non-invasive electrical impedance measurements. Such a technique would facilitate testing the biocompatibility of various materials,... more
Our aim is to establish an objective, easy-to-use technique to evaluate tissue irritation in vivo using non-invasive electrical impedance measurements. Such a technique would facilitate testing the biocompatibility of various materials, and also in quantifying skin diseases and other processes involving structural changes. It has been found that irritation of the oral mucosa not clinically or histologically discernible could be detected with a simple device based on electrical impedance techniques. Originally, the key problem was to focus the probing electrical field in order to minimize artefacts emanating from tissue layers of no interest. The device was then refined and applied to skin testing. It was found that irritation effects far below the limit of the commonly used visual readings could be detected. In this case, it is desirable to exclude from the measurement tissue layers with no diagnostic information, or at least reduce their influence. In this paper, the essential step...
Research Interests:
We determine the in-vivo dielectric properties—resistivity and relative permittivity—of living epidermis and dermis of human skin soaked with a physiological saline solution for one minute between 1 kHz and 1 MHz. This is done by fitting... more
We determine the in-vivo dielectric properties—resistivity and relative permittivity—of living epidermis and dermis of human skin soaked with a physiological saline solution for one minute between 1 kHz and 1 MHz. This is done by fitting approximate analytical solutions of a mechanistic model for the transport of charges in these layers to a training set comprising impedance measurements at two depth settings on stripped skin on the volar forearm of 24 young subjects. Here, the depth settings are obtained by varying the voltage at a second inject on the electrical-impedance-spectroscopy probe. The model and the dielectric properties are validated with a test set for a third depth setting with overall good agreement. In addition, the means and standard deviations of the thicknesses of living epidermis and dermis are estimated from a literature review as 61±7 μm and 1.0±0.2 mm respectively. Furthermore, extensions to resolve the skin layers in more detail are suggested.
Research Interests:
A mechanistic mathematical model for electrical impedance spectroscopy (EIS) measurements of human skin is analyzed, leading to a reduced model and approximate solutions. In essence, the model considers a complex-valued Laplace equation... more
A mechanistic mathematical model for electrical impedance spectroscopy (EIS) measurements of human skin is analyzed, leading to a reduced model and approximate solutions. In essence, the model considers a complex-valued Laplace equation in the frequency domain for the alternating current from a circular EIS probe passing through the layers – stratum corneum, viable skin and adipose tissue – of human skin in the frequency range 1 kHz – 1 MHz. The reduced model, which only needs to be solved numerically for the viable skin with modified boundary conditions, is verified with the full set of equations (non-reduced model): good agreement is found with a maximum relative error of less than 3%. A Hankel transform of the reduced model allows for approximate solutions of not only the measured impedance but also the point-wise potential distribution in the skin. In addition, the dimensionless numbers governing the EIS are elucidated and discussed.
Research Interests:
Research Interests:
Research Interests:
Bio-electrical impedance spectra of skin cancer and other lesions can be assessed using both regular non-invasive probes and a novel type of microinvasive electrode system with a surface furnished with tiny spikes that penetrate stratum... more
Bio-electrical impedance spectra of skin cancer and other lesions can be assessed using both regular non-invasive probes and a novel type of microinvasive electrode system with a surface furnished with tiny spikes that penetrate stratum corneum. The aim of the study was to compare the accuracy of detection for various types of skin cancer using impedance spectra measured with these two different electrode systems in an objective way without optimising the power of discrimination. Impedance spectra of 99 benign nevi, 28 basal cell carcinomas (BCC), and 13 malignant melanomas (MM) were measured using the two electrode systems. Classification of the lesions was made using Fisher's linear discriminant, and the sensitivities and specificities of the techniques were estimated using cross-validation. The best separation between nevi and BCC was achieved using the regular non-invasive probe (96% sensitivity and 86% specificity), whereas the best separation between nevi and MM was achieved using the microinvasive electrodes (92% sensitivity and 80% specificity). Our results indicate that the choice of electrode system is application dependent.
Research Interests:
27 Within and beyond the Skin Barrier as Seen by Electrical Impedance Stig Ollmar and ... 18.Martinsen, ØG, Grimnes, S., and Sveen, O., Dielectric properties of the epidermal stratum corneum ... Rantanen, I., Nicander, I., Jutila, K.,... more
27 Within and beyond the Skin Barrier as Seen by Electrical Impedance Stig Ollmar and ... 18.Martinsen, ØG, Grimnes, S., and Sveen, O., Dielectric properties of the epidermal stratum corneum ... Rantanen, I., Nicander, I., Jutila, K., Ollmar, S., Tenovuo, J., and Söderling, E., Betaine ...
Research Interests: Biomedical Engineering, Low Frequency, Humans, Female, Physiological, and 15 moreYoung Adult, Medical Physiology, Dielectric Properties, Mathematical Model, Functional integration, Electrical Properties, Time Factors, Electrodes, Stratum Corneum, Sodium Chloride, Physical Properties, Electrical And Electronic Engineering, Electric Impedance, Skinfold Thickness, and Electrical Impedance(Young Adult, Medical Physiology, Dielectric Properties, Mathematical Model, Functional integration, Electrical Properties, Time Factors, Electrodes, Stratum Corneum, Sodium Chloride, Physical Properties, Electrical And Electronic Engineering, Electric Impedance, Skinfold Thickness, and Electrical Impedance)
(Young Adult, Medical Physiology, Dielectric Properties, Mathematical Model, Functional integration, Electrical Properties, Time Factors, Electrodes, Stratum Corneum, Sodium Chloride, Physical Properties, Electrical And Electronic Engineering, Electric Impedance, Skinfold Thickness, and Electrical Impedance)
Research Interests: Biomedical Engineering, Near Infrared, Multivariate Analysis, Humans, Diabetes mellitus, and 12 moreNear Infrared Spectroscopy, Male, NIR spectroscopy, Skin, Aged, Middle Aged, Spectrum, Adult, Electrical And Electronic Engineering, Electric Impedance, Biological & Medical Sciences, and Diabetic complication
Research Interests: Biomedical Engineering, Near Infrared, Multivariate Analysis, Humans, Diabetes mellitus, and 12 moreNear Infrared Spectroscopy, Male, NIR spectroscopy, Skin, Aged, Middle Aged, Spectrum, Adult, Electrical And Electronic Engineering, Electric Impedance, Biological & Medical Sciences, and Diabetic complication
Research Interests:
Research Interests:
We present predictive models that can foresee how skin will react when exposed to chemicals. Skin impedance spectra, 31 frequencies between 1 and 1000 kHz at five depth settings, were collected before and after application of chemicals on... more
We present predictive models that can foresee how skin will react when exposed to chemicals. Skin impedance spectra, 31 frequencies between 1 and 1000 kHz at five depth settings, were collected before and after application of chemicals on volar forearms of volunteers. Tegobetaine and sodium lauryl sulphate were used to induce the irritations. The spectra were filtered using orthogonal signal
Research Interests: Chemical Engineering, Data Mining, Principal Component Analysis, Statistical Analysis, Regression Analysis, and 11 moreFrequency, Skin, Predictive models, Prediction Model, Impedance, LASER SINTERING, Partial Least Squares Regression, Multivariate Regression, Orthogonal signal correction, Sodium Lauryl Sulphate, and Least squares method
ABSTRACT
Research Interests:
Depending on the frequency range, electrical bio-impedance (EBI) spectra of skin reflect the hydration of the stratum corneum, experimental irritative and allergic reactions, skin barrier properties, and alterations due to some diseases.... more
Depending on the frequency range, electrical bio-impedance (EBI) spectra of skin reflect the hydration of the stratum corneum, experimental irritative and allergic reactions, skin barrier properties, and alterations due to some diseases. For oral mucosa, the degree of keratinization is an important factor. Baseline values differ while reactions are reflected in a manner similar to skin. Patterns of indices can
Research Interests:
Research Interests:
BACKGROUND/AIMS: In a previous study we mapped differences in electrical impedance between different anatomical locations related to age and sex. Now we employ the electrical impedance technique for studying the seasonal variations for... more
BACKGROUND/AIMS: In a previous study we mapped differences in electrical impedance between different anatomical locations related to age and sex. Now we employ the electrical impedance technique for studying the seasonal variations for the same skin sites. METHOD: The investigation was performed on 48 healthy volunteers divided into two groups on the basis of sex. Readings of electrical impedance were taken from ten different body locations at each of the four seasons during one year. Electrical impedance spectra were measured in the frequency range 1 kHz to 1 MHz, and four impedance indices based on the complex impedance values at 20 kHz and 500 kHz were calculated. RESULTS: The baseline values varied from one site to another and increased significantly for most sites from the winter to the summer, while the changes from October to March were negligible. Using ANOVA, the seasonal variation was found to be a more important factor than sex. CONCLUSIONS: Our results suggest that seasonal variations for different skin sites should be taken into consideration when using the electrical impedance technique.
Research Interests:
Research Interests:
In an earlier study, we have shown that the electrical impedance (IMP) is dependent on the lipid content of the stratum corneum as studied by lipid extraction. Therefore, we now employ the IMP technique to compare the properties of... more
In an earlier study, we have shown that the electrical impedance (IMP) is dependent on the lipid content of the stratum corneum as studied by lipid extraction. Therefore, we now employ the IMP technique to compare the properties of clinically normal atopic skin with that of non-atopic skin. We looked at the same time at concomitant alterations in transepidermal water loss (TEWL) and skin moisture results. Twenty-two healthy participants and 26 patients with atopic dermatitis were recruited. One test site on each volar forearm was used in the test procedure, of cyclohexane swabbing, skin stripping, and lipid extraction using a mixture of hexane:isopropanol. Responses were evaluated by measuring TEWL, skin moisture using electrical capacitance, and finally IMP spectroscopy in the frequency range 1 kHz to 1 MHz before the start of the study, after each step of the test procedure, and also during a 2 weeks recovery period. Only the IMP results showed significant changes between baseline values of clinically normal atopic skin and healthy skin. Furthermore, IMP and TEWL showed significantly larger reactivity for the atopic group after the skin stripping procedure, and IMP after lipid extraction as well. Our results show that IMP is a useful method for detection of changes in the lipid content of the stratum corneum by discriminating healthy looking atopic skin from healthy control skin, and to detect changes in reactivity between the two groups.
Research Interests:
Research Interests:
Modern pacemakers (implantable devices used for maintaining an appropriate heart rate in patients) can use an intracardiac ventricular impedance signal for physiological cardiac stimulation control. Intracardiac ventricular impedance from... more
Modern pacemakers (implantable devices used for maintaining an appropriate heart rate in patients) can use an intracardiac ventricular impedance signal for physiological cardiac stimulation control. Intracardiac ventricular impedance from nine animal subjects is analysed and presented (seven sheep: 49.0 +/- 6.5 kg, sinus rhythm 100.3 +/- 16.5 beats min(-1), average impedance 629.8 +/- 72.6 ohms; and two dogs: 30 kg each, sinus rhythm 86.0 beats min(-1), 862.1 ohms and 134.0 beats min(-1), 1114.6 ohms, respectively). The averaged curve and standard deviation curve of the impedance in sinus rhythm were analysed in MATLAB to clarify and study consistent impedance shape over one heart cycle. In eight of nine (89%) animal subjects, a consistent impedance slope change (notch) was observed in the early stage of the cardiac filling phase. This result was reproduced in an additional subject with simultaneous echocardiographical measurements of mitral valve blood flow. The notch occured soon after rapid early filling (E-wave in mitral flow) but prior to ventricular filling caused by atrial contraction, indicating that the impedance notch was caused by rapid ventricular filling and that it might be a sensed feature of diagnostic value. The intracardiac impedance notch in the present study had similar features to the non-invasive transthoracic impedance O-wave reported by others, and it is shown here that an O-wave is found in intracardiac impedance signals, strongly suggesting that the non-invasive O-wave is caused by cardiac events.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
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... more
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.
Research Interests:
Clinically relevant information in electrical skin impedance spectra is diluted by the electrical properties of stratum corneum. Eliminating stratum corneum would improve the signals from the tissue. The aim of this paper is to describe... more
Clinically relevant information in electrical skin impedance spectra is diluted by the electrical properties of stratum corneum. Eliminating stratum corneum would improve the signals from the tissue. The aim of this paper is to describe and investigate a new type of skin impedance probe with a dedicated surface structure that penetrates through stratum corneum but not into dermis, called the
Research Interests:
... Gondran et al., Medical & Biological Engineering & Computing, May 1995 [5] An Active, Microfabricated, Scalp Electrode-Array for EEG Recording, Babak Alizadeh-Taheri, Rosemary L.... more
... Gondran et al., Medical & Biological Engineering & Computing, May 1995 [5] An Active, Microfabricated, Scalp Electrode-Array for EEG Recording, Babak Alizadeh-Taheri, Rosemary L. Smith, and Robert T. Knight, Sensors and Actuators A54, Elsevier Science SA, 1996 [6] Low ...
Research Interests:
Research Interests:
Our aim is to establish an objective, easy-to-use technique to evaluate tissue irritation in vivo using non-invasive electrical impedance measurements. Such a technique would facilitate testing the biocompatibility of various materials,... more
Our aim is to establish an objective, easy-to-use technique to evaluate tissue irritation in vivo using non-invasive electrical impedance measurements. Such a technique would facilitate testing the biocompatibility of various materials, and also in quantifying skin diseases and other processes involving structural changes. It has been found that irritation of the oral mucosa not clinically or histologically discernible could be detected with a simple device based on electrical impedance techniques. Originally, the key problem was to focus the probing electrical field in order to minimize artefacts emanating from tissue layers of no interest. The device was then refined and applied to skin testing. It was found that irritation effects far below the limit of the commonly used visual readings could be detected. In this case, it is desirable to exclude from the measurement tissue layers with no diagnostic information, or at least reduce their influence. In this paper, the essential step...