Electrosurgery and Temperature Increase in Tissue With a Passive Metal Implant.

During monopolar electrosurgery in patients, current paths can be influenced by metal implants, which can cause unintentional tissue heating in proximity to implants. Guidelines concerning electrosurgery and active implants such as pacemakers or implantable cardioverter defibrillators have been published, but most describe interference between electrosurgery and the active implant rather than the risk of unintended tissue heating. Tissue heating in proximity to implants during electrosurgery may cause an increased risk of patient injury.

Comparison between the AC and DC measurement of electrodermal activity.

Recording electrodermal activity is a well-accepted physiological measurement for clinical approaches and research. Historically, applying a DC (direct current) signal to the skin to measure the conductance is the most common practice for exogenous recordings. However, this method can be subject to error due to electrode polarization even with "nonpolarizing" electrodes-a problem that can be eliminated with alternating current (AC) methodology.

Bioimpedance-based respiration monitoring with a defibrillator.

Defibrillators often use an ac measurement to ensure safe electrode placement. Some defibrillators also utilize impedance measurements for ventilation monitoring. This paper investigates how such measurements can be optimized for high respiration sensitivity and finds that it is beneficial to add two extra electrodes in addition to the two defibrillator electrodes.

Estimation of skin conductance at low frequencies using measurements at higher frequencies for EDA applications.

Using low-frequency (LF) alternating current skin conductance (SC) has recently been recommended for electrodermal activity (EDA) measurement, but the method may imply some limitations in sampling rate, which are insufficient for capturing the complete SC waveform. The aim of this study was to assess whether LF SC can be estimated based on skin admittance (SA) measurements at higher frequencies allowing higher sampling rates. SA measurements from 1 Hz to 70 kHz were gathered from 20 healthy human participants, and an interval from 500 Hz to 10 kHz was used to fit a Cole model to the measured SA by means of the nonlinear least squares method.

Tumescent suction curettage vs. curettage only for treatment of axillary hyperhidrosis evaluated by subjective and new objective methods.

The main purpose of this study was to compare the effect of the 2 minimally invasive surgical techniques for treating axillary hyperhidrosis: superficial tumescent suction curettage and curettage only. A total of 22 patients diagnosed with axillary hyperhidrosis received one type of treatment at each side, randomized. Examinations were performed pre-operatively and at 3, 6 and 12 months following treatment.

Waveform difference between skin conductance and skin potential responses in relation to electrical and evaporative properties of skin.

The shapes of skin conductance (SC) and skin potential (SP) responses are often similar, but can also be very different due to an unexplained cause. Using a new method to measure SC and SP simultaneously at the same electrode, this difference was investigated in a new way by comparing their temporal peak differences. SC, SP, skin susceptance (SS), and transepidermal water loss (TEWL) were recorded from 40 participants during relaxation and stress.

Improved estimation of sweating based on electrical properties of skin.

Skin conductance (SC) has previously been reported to correlate strongly with sweat rate (Swr) within subjects, but weakly between subjects. Using a new solution for simultaneous recording of SC, skin susceptance (SS) and skin potential (SP) at the same skin site, the aim of this study was to assess how accurately sweat production can be estimated based on combining these electrical properties of skin. In 40 subjects, SC, SS, SP and Swr by skin water loss was measured during relaxation and mental stress.

Publication recommendations for electrodermal measurements.

This committee was appointed by the SPR Board to provide recommendations for publishing data on electrodermal activity (EDA). They are intended to be a stand-alone source for newcomers and experienced users. A short outline of principles for electrodermal measurement is given, and recommendations from an earlier report (Fowles et al.

Bioimpedance for pain monitoring during cutaneous photodynamic therapy: Preliminary study.

Background: Pain is a well-known problem associated with light exposure during topical photodynamic therapy (PDT). Different methods for dealing with the pain have been developed over the past years, ranging from cooling with air or water to nerve blocking. However, the mechanisms responsible for the pain induction have not yet been fully understood.

Evaluation of algorithms for calculating bioimpedance phase angle values from measured whole-body impedance modulus.

This paper addresses the problem of calculating the bioimpedance phase angle from measurements of impedance modulus. A complete impedance measurement was performed on altogether 20 healthy persons using a Solatron 1260/1294 system. The obtained impedance modulus (absolute impedance value) values were used to calculate the Cole parameters and from them the phase angles.

New method for separation of electrode polarization impedance from measured tissue impedance.

In this paper we have shown that electrode polarization impedance (EPI) can be separated from measured tissue impedance as long as the characteristic frequencies of EPI and tissue are not too close, so that the EPI is largely displayed as a separate dispersion. In 2-electrode measurements the EPI and sample are physically connected in series, and commonly modelled by equivalent components in series. We have calculated the parallel equivalent elements and converted the series connected EPI and sample to a parallel admittance model.

Electrodermal activity by DC potential and AC conductance measured simultaneously at the same skin site.

Background: For a long time, DC conductance has been the most important parameter in electrodermal routine measurements. However, DC current flow polarizes the electrodes, electrolyzes the skin, disturbs the measurement of conductance by possible varying electromotive forces (EMFs) in the circuit, and impedes the registration of the skin endosomatic DC potential.

Methods: We therefore present a measuring system where DC current was replaced by a small AC current in a monopolar system, enabling the DC potential and AC conductance to be measured simultaneously at the same skin site.

A study on electrode gels for skin conductance measurements.

Low-frequency skin conductance is used within several clinical applications and is mainly sensitive to sweating and the moisture content of the stratum corneum, but also how electrodes introduce changes in the electrical properties. Four electrode gels were investigated with regard to sorption characteristics and electrical properties. Skin conductance time series were collected from 18 test subjects during relaxation, exercise and recovery, wearing different pairs of electrodes contralaterally on the hypothenar and the T9 dermatome.

Early detection of cardiac ischemia using a conductometric pCO(2) sensor: real-time drift correction and parameterization.

For detection of cardiac ischemia based on regional pCO(2) measurement, sensor drift becomes a problem when monitoring over several hours. A real-time drift correction algorithm was developed based on utilization of the time-derivative to distinguish between physiological responses and the drift, customized by measurements from a myocardial infarction porcine model (6 pigs, 23 sensors). IscAlert conductometric pCO(2) sensors were placed in the myocardial regions supplied by the left anterior descending coronary artery (LAD) and the left circumflex artery (LCX) while the LAD artery was fully occluded for 1, 3, 5 and 15 min leading to ischemia in the LAD-dependent region.

A new approach for an estimation of the equilibrium stratum corneum water content.

Background/purpose: Water content is the most vital parameter governing the overall function of the epidermal stratum corneum (SC). Thus, knowledge of the in vivo absolute water content of the SC is of great interest.

Methods: We have investigated a non-invasive method for the estimation of in vivo SC water content based on transepidermal water loss measurements combined with desorption studies of SC in vitro, by means of a dynamic vapour sorption setup where relative humidity (RH) and temperature are controlled.

Electrical impedance of stainless steel needle electrodes.

We present experimental findings regarding variability and stability of the electrical impedance properties of medical grade stainless steel needle electrodes in vitro. Monopolar impedance spectra (1 Hz to 1 MHz) were measured and scanning electron microscope images were obtained for five needle types with active electrode area from 0.28 to 0.

Invasive electrical impedance tomography for blood vessel detection.

We present a novel method for localization of large blood vessels using a bioimpedance based needle positioning system on an array of ten monopolar needle electrodes. The purpose of the study is to develop a portable, low cost tool for rapid vascular access for cooling and controlled reperfusion of cardiac arrest patients. Preliminary results show that localization of blood vessels is feasible with this method, but larger studies are necessary to improve the technology.

Current threshold for nerve stimulation depends on electrical impedance of the tissue: a study of ultrasound-guided electrical nerve stimulation of the median nerve.

Background: Understanding the mechanisms causing variation in current thresholds for electrical nerve stimulation may improve the safety and success rate of peripheral nerve blocks. Electrical impedance of the tissue surrounding a nerve may affect the response to nerve stimulation. In this volunteer study, we investigated the relationship between impedance and current threshold needed to obtain a neuromuscular response.

Stratum corneum in vivo water content from TEWL-measurements.

In this paper we present a new pilot-study on the possibility of finding in vivo absolute water content of the stratum corneum (SC) non-invasively. The method is based on measurements of trans-epidermal-water-loss (TEWL) after an occlusion process of the SC. Based on the desorption curves from the occluded skin, estimates of absolute water content of the SC can be made by assuming a similar, but hypothetical, desorption of non-occluded SC.

Embedded instrumentation for skin admittance measurement.

Skin admittance measurements are used in several biomedical applications, and the technology available today opens for new design solutions. The digital instrumentation has several advantages to the conventional analog instrumentation by needing fewer components, having lower cost, better reliability and is easier to modify in the field. A design alternative is presented which uses an 8-bit microcontroller and few extra components for skin admittance instrumentation.

Determination of tissue type surrounding a needle tip by electrical bioimpedance.

A novel method for determining needle position based on local tissue impedance and electrode polarization data, is presented. Measurements of electrical impedance in a small volume around a needle tip can aid in determining if the needle is in the desired tissue. There are many possible applications for this technique, such as needle positioning when administering drugs in blood vessels or muscle tissue, for epidural analgesia or needle EMG exams.

Impedance-based tissue discrimination for needle guidance.

Measurement of electrical impedance can discriminate between tissues of different electrical properties. A measurement system with adequate spatial resolution focused on a volume around the tip of a needle or other invasive clinical equipment can be used to determine in which type of tissue the tip is positioned. We have measured the sensitivity zone of a needle electrode with an active electrode area of 0.

Electrical measurement of sweat activity.

A multichannel logger for long-term measurements of sweat activity is presented. The logger uses skin surface electrodes for unipolar admittance measurements in the stratum corneum. The logger is developed with emphasis on clinical use.

Water sorption and electrical properties of a human nail.

Background/purpose: Water absorption is important for the overall function of keratinized tissues like the stratum corneum and nail. Hence, measurement of water sorption dynamics and water content of these tissues is of great interest.

Methods: We have studied water sorption and electrical properties of a human nail in a measuring cell where the temperature and relative hydration could be controlled.

Gravimetric method for in vitro calibration of skin hydration measurements.

A novel method for in vitro calibration of skin hydration measurements is presented. The method combines gravimetric and electrical measurements and reveals an exponential dependency of measured electrical susceptance to absolute water content in the epidermal stratum corneum. The results also show that absorption of water into the stratum corneum exhibits three different phases with significant differences in absorption time constant.