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S Ollmar

Publications and source records attributed to S Ollmar.

17 recordsLinked to original sources
PubMed2003

Combined near-infrared spectroscopy and multifrequency bio-impedance investigation of skin alterations in diabetes patients based on multivariate analyses.

A group of 34 diabetic men, with different degrees of diabetes complications, including skin changes, were studied by near-infrared (NIR) spectroscopy and total body multi-frequency bio-impedance analyses (MFBIA-body). Skin reflectance spectra were measured with a fibre-optic probe in four locations (sites): hand, arm, leg and foot. As control subjects, a group of 23 healthy males were also measured. A combined multivariate analysis of the two types of spectrum was performed. It was concluded that the NIR method has the potential to detect diabetes-related skin conditions and also that the combination of the two techniques provides a higher potential for classification and discrimination of the skin conditions, with correct classification increasing from 63% to 85%.

Adult↗
PubMed2002

Analysis of the O-wave in acute right ventricular apex impedance measurements with a standard pacing lead in animals.

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.

Animals↗
PubMed1999

Electrical bioimpedance related to structural differences and reactions in skin and oral mucosa.

Electrical bioimpedance can reflect structural and chemical changes of the skin and the oral mucosa in the beta-dispersion frequency range. From our measured multifrequency data set, four physically distinct indices have been formulated to distinguish the electrical properties for different anatomical locations and to detect different reactions and conditions of the skin and the oral mucosa. In comparison with the skin, the differences for various anatomical regions were greater in the oral cavity, which showed as well a different impedance pattern after irritant responses. We conclude that the impedance technique is able to classify and quantify different responses and conditions, preferably by using contralateral reference sites, or following a site in time; however, mapping of baseline properties facilitates the use of the method even if a large part of the skin or the oral mucosa is involved. The method has the potential of becoming a diagnostic decision support tool.

Adult↗
PubMed1999

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.

Adolescent↗
PubMed1998

Volumetric determination of normal and scoliotic vertebral bodies.

A new method is presented for stereological evaluation of the volume of the vertebral body in vivo. The height of the vertebral body is measured at three standardised points on an anteroposterior radiograph and at two other points on a lateral one. The area of the body is also measured using a special grid superimposed on a CT scan from the middle part of the vertebra. The volume of the vertebral body is then calculated using Cavalieri's principle for irregular objects: V = delta a x H, where V is the volume of the vertebral body, delta a is the mean cross-section surface area on the CT scan and H is the mean of the heights at the five points on the radiographs, computed as mean weighted circumferential height. The volume of one normal and one scoliotic vertebra was evaluated in vitro using this formula. The obtained values were compared with the values derived from serial CT scans of the two vertebrae. The results showed that the volume of the normal vertebra measured with our new method was 15.9 cm3 and measured with serial CT scans using the same grid it was 15.07 cm3. For the scoliotic vertebra the values were 17.6 and 17.3 cm3, respectively. The degree of accuracy of the measurements with the presented method as compared with the serial CT method was 95% for the normal and 98.5% for the scoliotic vertebra. To prove the clinical applicability of the method, the heights of the apical and of the upper and the lower end vertebrae of the curve and the volume of the apical vertebrae were evaluated in eight scoliotic girls (nine curves) before and 3 years after spinal instrumentation and posterior fusion. The results showed that the mean circumferential height of the three vertebrae had increased significantly at the last follow-up. The volume of the apical vertebra had also increased, but the difference was not significant. It is concluded that the described method is easy to apply and has satisfactory accuracy for in vivo longitudinal studies of the volume of the vertebral body on radiographs and CT scans.

Adolescent↗
PubMed1998

Electrical impedance of nodular basal cell carcinoma: a pilot study.

BACKGROUND: Previously, we have explored the use of measurements of electrical impedance and devised 4 physically distinct indices named magnitude index (MIX), phase index, real part index and imaginary part index (IMIX) from the impedance data. Our results indicated that these indices could characterize contact reactions. OBJECTIVE: The goal of the present study was to use the electrical impedance method for the preoperative assessment of nodular basal cell carcinoma (BCC). METHODS: We included 11 patients with a total of 12 nodular BCC, diagnosed clinically and histologically. The noninvasive measurements were performed by transepidermal water loss (TEWL) and electrical impedance. For reference, normal looking contralateral or ipsilateral skin was used. RESULTS: Compared to controls, the mean TEWL of BCC was increased, but this finding was not statistically significant. The electrical impedance measurements of BCC tissue revealed statistically significant changes of the impedance indices MIX and IMIX (p </=0.001). CONCLUSION: The results suggest that the measurement of electrical impedance might become useful for investigations of BCC.

Aged↗
PubMed1997

Information in full and reduced data sets of electrical impedance spectra from various skin conditions, compared using a holographic neural network.

Information relating to patho-physiological events in living tissues, including skin, should be found in the beta-dispersion frequency range of the electrical impedance. For intact skin, the alpha-dispersion is strongly influenced by the condition of the stratum corneum, particularly its hydration. For intact skin, these dispersions are not well separated: in a Nyquist plot, most of the relatively small beta-dispersion will be hidden behind the upper-frequency end of the alpha-dispersion arc. In the study, information obtained with a set of four indices, claimed to extract most of the information in the pertinent frequency interval, is compared with the full information measured at 31 frequencies, between 1 kHz and 1 MHz, for irritant and allergic contact reactions and nodular basal cell carcinomas, using a holographic neural network that appears to be useful for model-independent evaluation of the consequences of data-reduction procedures. Cole parameters should be avoided in the beta-range for intact skin. The indices are well supported, as long as differences from a reference site are used, and it seems that they can serve as the basis for differential diagnostics even as absolute values, although more information may be extracted from the complete spectrum.

Diagnosis, Differential↗
PubMed1997

Electrical impedance. A method to evaluate subtle changes of the human oral mucosa.

In a previous study, we mapped the differences in electrical impedance between various anatomical locations in the oral mucosa. We now explore the ability of the impedance technique to detect mild reactions in the buccal mucosa induced by the irritant sodium lauryl sulphate. This substance was applied for 15 min at a concentration of 2% to the mucosa of 26 healthy subjects. A contralateral site was used as a control. Responses were evaluated by measuring electrical impedance before exposure and after removal of the irritant, and also by visual inspection and histology. Magnitude and phase of impedance were determined in the frequency range 1 kHz to 1 MHz at 5 depth settings, and 4 physically distinct indices were calculated from the impedance data. The results showed the response to be at its maximum 5 min after removal of the test chamber, for all indices. These changes were statistically significant, whereas visual and histological alterations were slight or negligible. We conclude that the electrical impedance technique is capable of detecting mucosal changes in the invisible or barely visible range, and that the mucosal response to sodium lauryl sulphate is well characterised by the 4 indices.

Adult↗
PubMed1997

Electric impedance measurements at six different anatomic locations of macroscopically normal human oral mucosa.

We have used an electric impedance technique to explore the properties of the oral mucosa at various sites in the normal mouth. Investigations were performed on 26 healthy non-smoking subjects at 12 test areas, representing a range of mucosal types. Electric impedance spectra were measured in the frequency range 1 kHz to 1 MHz at five depth penetration settings of the instrument, and four indices were calculated for each depth. Statistically significant differences in the indices were found between most of these locations but not between contralateral sites at a similar position. The differences between some areas were considerably greater, and the differences between contralateral sites were smaller, than those encountered in the skin. Our results suggest that the choice of site for investigation of the oral cavity is more critical than with experimentation on the skin and that cognizance of this fact makes the oral cavity readily available for studies by the impedance method.

Adult↗
PubMed1996

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.

Adolescent↗
PubMed1996

Correlation of impedance response patterns to histological findings in irritant skin reactions induced by various surfactants.

We have explored the use of measurements of electrical impedance to discriminate between the effects of different irritant substances upon the skin, and have studied the relationships between impedance and histopathological change. Three compounds with different chemical profiles were tested on volunteers: sodium lauryl sulphate, benzalkonium chloride and nonanoic acid. The concentrations selected were such that each irritant produced responses of a similar order, as judged by visual scores. The magnitude and phase of electrical impedance were measured and, for comparison, also the transepidermal water loss. Four physically distinct aspects (indices) were devised from the impedance data, and the values obtained were statistically analysed. The three irritants produced different effects, giving distinctive impedance patterns. These were also found to be reflected by three different types of histopathological skin response. Our results suggest that the indices can be used to classify irritant contact reactions, which it is difficult or impossible to achieve by other non-invasive techniques.

Adult↗
PubMed1995

Electrical impedance measured to five skin depths in mild irritant dermatitis induced by sodium lauryl sulphate.

The non-invasive electrical impedance technique used in this study reflects structural changes in a tissue, and provides an estimate of the level of oedema by a simple impedance index. Sodium lauryl sulphate (SLS), dissolved in water at concentrations of 0.1, 0.5 and 2.0%, was applied for 24 h in 12 mm Finn chambers on both volar forearms of 12 healthy volunteers. An unoccluded area was used as a reference site. Readings from all sites were taken before the application of the irritant, and 24 h after its removal. After the last reading, a 3-mm punch biopsy was taken from each test site for histological examination. The results obtained from electrical impedance measurements at five different skin depths were correlated with those obtained from histological examination, visual scoring and transepidermal water loss (TEWL). For all of the methods used the responses were proportional to the concentration of the irritant. Statistically significant changes of electrical impedance were found for all depths and concentrations, except for 0.1% SLS at the most superficial depth. The histological changes were focused in the epidermis, and mainly consisted of oedema. Alterations in the thickness of the epidermis due to oedema were used as a quantitative parameter for correlation with the assessment of irritation using the electrical impedance technique. For the detection of irritant reactions, TEWL and electrical impedance are more sensitive than visual scoring, and selection of the optimum depth penetration further increases the sensitivity of the electrical impedance measurement.

Adult↗
PubMed1995

Electrical impedance for estimation of irritation in oral mucosa and skin.

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 steps of the development of a multi-frequency depth selective device are reviewed.

Artifacts↗
PubMed1994

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.

Adult↗
PubMed1993

Electrical impedance index in human skin: measurements after occlusion, in 5 anatomical regions and in mild irritant contact dermatitis.

The electrical impedance in 23 healthy volunteers at 2-6 different skin sites was measured with a new impedance device, which makes possible non-invasive local measurements to a controlled depth. In 11 subjects, the test sites were occluded for 24 h using empty Finn Chambers and chambers with water, physiological saline, a paper disc or 0.002% sodium lauryl sulfate (SLS). In the normal skin of 10 subjects, the electrical impedance was measured from 5 different body areas for 5 consecutive days. In 3 subjects, daily measurements for 1 month were done, both from normal skin and from skin following the application of 2% SLS. The results show that the irritation index based on electrical skin impedance gives little day-to-day variation at one and the same test site, in comparison to the variations between different test sites on the same subject and the interindividual variations observed. Significant differences in impedance values between different anatomical regions of normal skin were found. Occlusion does not affect readings taken 24 h or later after removal, but increases variance for readings taken 1 h after removal. Effects on the skin of mild irritation and its recovery phase are easily monitored with the new device. Technology based on electrical impedance, in its newly presented form, with the advantages of improved geometrical definition and depth control, can be used as an objective tool to measure skin irritation. For detection of subclinical irritant contact dermatitis, repeated readings taken over several days may be needed.

Adult↗
PubMed1992

Electrical impedance applied to non-invasive detection of irritation in skin.

Healthy volunteers were subjected to irritation by sodium lauryl sulphate at concentrations in the range 0.002% to 5.0% applied in Finn Chambers for 24 h. Test sites were visually assessed 1 h and 24 h after cessation of exposure. At the same times electrical impedance was measured with a new impedance device which allows non-invasive local measurements to a controlled depth. Close agreement between concentration and an irritation index calculated from electrical impedance parameters was found over the whole concentration range for most test persons. At concentrations below 0.2%, visual scores were zero. These results suggest that electrical impedance can be used as an objective tool to record irritation, and further that electrical impedance might be a more sensitive method than the commonly used visual readings.

Adolescent↗