Biomedical subjects
Publications and source records attributed to S Grimnes.
A vehicle with 16 electrodes for the two-dimensional electrical admittance mapping of human skin is presented. Measurements on 20 test subjects have been carried out and analyzed for the possible detection of line patterns in the electrical properties of the skin, claimed to coincide with the so-called acupuncture meridian lines of ancient Chinese medicine. No such lines were found.
Some of the views presented in the chapter on 'Examination of stratum corneum hydration state by electrical methods' in Skin Bioengineering - Techniques and Applications in Dermatology and Cosmetology (Karger, 1998) are in strong disagreement with the results from basic research that has been conducted on skin impedance measurement over the last decades. This research has e.g. non-ambiguously shown that the frequency response of the stratum corneum does not obey the Cole equation and that measurement depth is strongly dependent on measurement frequency. One consequence of these findings is that multifrequency electrical measurements on stratum corneum are impossible to achieve in vivo with any electrode system known today. Hence, electrical measurements of stratum corneum hydration must be conducted at one single, low frequency.
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Blister-skin and warts have been studied as possible sources of 'pure' stratum corneum without sweat ducts. The purpose of the study was to assess whether the DC electrical conductance measured on human skin is totally dominated by the sweat ducts, or is also significantly contributed to by the stratum corneum itself. By means of galvanic skin response (GSR) measurements, these tissues were found to be unrealiable as sources of 'pure' stratum corneum. This is because they displayed significant GSR waves, and hence should have some form of active pores. However, measurements on blister-skin and nail in situ revealed a substantial frequency independent electrical conductance at frequencies typically below 10 Hz.
Some electrical properties of human hair have been investigated to determine whether a significant DC electrical conductance is present in keratinised tissues. The DC conductance was found to be substantial and highly dependent on the moisture level in the hair fibres. At high moisture levels, the conductance was found to be almost frequency independent below 1 kHz. Absorption and desorption profiles were also monitored, revealing different stages of sorption mechanisms in the fibres. Although absorption was found to be a slow process with 'time constants' in the range of hours, desorption was much faster, in the range of a few minutes.
Modern anaesthetic machines are equipped with several safety components to prevent delivery of hypoxic mixtures. However, such a technical development has increased the complexity of the equipment. We report a reconstructed anaesthetic machine in which a paramagnetic oxygen analyzer has provided the means to simplify the apparatus. The new machine is devoid of several components conventionally included to prevent hypoxic mixtures: oxygen failure protection device, reservoir O2 alarm, N2O/air selector, and proportioning system for oxygen/nitrous oxide delivery. These devices have been replaced by a simple safety system using a paramagnetic oxygen analyzer at the common gas outlet, which in a feed-back system cuts off the supply of nitrous oxide whenever the oxygen concentration falls below 25%. The simplified construction of the anaesthetic machine has important consequences for safety, cost and user-friendliness. Reducing the complexity of the construction also simplifies the pre-use checkout procedure, and an efficient 5-point check list is presented for the new machine.
Skin sites on 8 test subjects were treated with moisturizers, and different electrical measuring methods were compared regarding their quality in the assessment of the induced changes in the stratum corneum hydration level. Low frequency susceptance measurements were found preferable to high frequency admittance measurements, and the advantages of monopolar measurements with the three-electrode system are described.
Although it is generally acknowledged that a pre-use checkout of the anaesthetic machine significantly improves patient safety, an evaluation of such procedures is uncommon. Previous studies have shown that anaesthetic personnel using different check routines are unable to detect the majority of pre-set technical malfunctions. We have shown that it is possible to develop an effective and time-saving check procedure by integrating seven simple steps into one continuous flow procedure, where the settings and results of one step are used in the following step to optimize step interaction. The method is a 'core' procedure adapted to machines sold after 1980 according to the current ISO standard (presently undergoing revision). A user inquiry demonstrated that this pre-use check has been easily adopted in departments of anaesthesia. Moreover, the inquiry showed that most departments would not accept a checkout procedure which required more than 5-6 min. A study on nurse anaesthetists performing this procedure in the operating suite showed an average checking time of approximately 3 min. A performance test was undertaken by activating four different malfunctions in an anaesthetic machine training simulator. Twelve of 17 nurse anaesthetists rapidly identified all faults, whereas five nurses missed one or two faults. Our study suggests that our check procedure (the seven point check) provides a time-saving method for effective pre-use control of the anaesthetic machine.
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The pathways of electric current have been examined with special electrodes and methods. The results indicate that the flow through ordinary stratified stratum corneum is negligible, and that the dominant ionic path is through the sweat duct units. Here the cells of interest may be oriented perpendicular to the main stratified orientation of the skin, and this may affect the methods and interpretations of absorption/permeability studies.
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The human threshold of sensation of 50 Hz current has hitherto been considered to be around 1 mA. A new sensing mechanism is reported which lowers the threshold about 3 decades. It is elicited when the skin slides on the current carrying conductor, and the sensation disappears when the skin is wet. The sensation is a feeling of vibration or increased surface roughness. The sensing mechanism has been shown to be due to electrostatic forces in the skin caused by the electric field in a poorly conducting stratum corneum. The mechanism is primarily potential dependent, and the absolute threshold of sensation has been found to be about 1.5 volt or 0.15 mu A rms at 50 Hz. In practical daily-life situations it is shown that 82% of 40 test subjects were able to sense a current of 2 mu A rms, 50 Hz.