Wearable Alcohol Monitoring Device for the Data-Driven Transcutaneous Alcohol Diffusion Model.

Wearable alcohol monitoring devices demand noninvasive, real-time measurement of blood alcohol content (BAC) reliably and continuously. A few commercial devices are available to determine BAC noninvasively by detecting transcutaneous diffused alcohol. However, they suffer from a lack of accuracy and reliability in the determination of BAC in real time due to the complex scenario of the human skin for transcutaneous alcohol diffusion and numerous factors (e.g., skin thickness, kinetics of alcohol, body weight, age, sex, metabolism rate, etc.). In this work, a transcutaneous alcohol diffusion model has been developed from real-time captured data from human wrists to better understand the kinetics of diffused alcohol from blood to different skin epidermis layers. Such a model will be a footprint to determine a base computational model in larger studies. Eight anonymous volunteers participated in this pilot study. A laboratory-built wearable blood alcohol content (BAC) monitoring device collected all the data to develop this diffusion model. The proton exchange membrane fuel cell (PEMFC) sensor was fabricated and integrated with an nRF51822 microcontroller, LMP91000 miniaturized potentiostat, 2.4 GHz transceiver supporting Bluetooth low energy (BLE), and all the necessary electronic components to build this wearable BAC monitoring device. The %BAC data in real time were collected using this device from these volunteers' wrists and stored in the end device (e.g., smartphone). From the captured data, we demonstrate how the volatile alcohol concentration on the skin varies over time by comparing the alcohol concentration in the initial stage (= 10 min) and later time (= 100 min). We also compare the experimental results with the outputs of three different input profiles: piecewise linear, exponential linear, and Hoerl, to optimize the developed diffusion model. Our results demonstrate that the exponential linear function best fits the experimental data compared to the piecewise linear and Hoerl functions. Moreover, we have studied the impact of skin epidermis thickness within ±20% and demonstrate that a 20% decrease in this thickness results in faster dynamics compared to thicker skin. The model clearly shows how the diffusion front changes within a skin epidermis layer with time. We further verified that 60 min was roughly the time to reach the maximum concentration, Cmax, in the stratum corneum from the transient analysis. Lastly, we found that a more significant time difference between BACmax and Cmax was due to greater alcohol consumption for a fixed absorption time.

Comparison of Circular and Rectangular-Shaped Electrodes for Electrical Impedance Myography Measurements on Human Upper Arms.

Electrical Impedance Myography (EIM) is a painless, noninvasive approach for assessing muscle conditions through the application of a high-frequency, low-intensity current to the muscle region of interest. However, besides muscle properties, EIM measurements vary significantly with changes in some other anatomical properties such as subcutaneous skin-fat (SF) thickness and muscle girth, as well as non-anatomical factors, such as ambient temperature, electrode shape, inter-electrode distance, etc. This study has been conducted to compare the effects of different electrode shapes in EIM experiments, and to propose an acceptable configuration that is less dependent on factors other than the cellular properties of the muscle. Initially, a finite element model with two different kinds of electrode shapes, namely, rectangular (the conventional shape) and circular (the proposed shape) was designed for a subcutaneous fat thickness ranging from 5 mm to 25 mm. The study concludes, based on the FEM study, that replacing the conventional electrodes with our proposed electrodes can decrease the variation in EIM parameters due to changes in skin-fat thickness by 31.92%. EIM experiments on human subjects with these two kinds of electrode shapes validate our finite element simulation results, and show that circular electrodes can improve EIM effectiveness significantly, irrespective of muscle shape variation.

Assessment of Optimized Electrode Configuration for Electrical Impedance Myography Using Genetic Algorithm via Finite Element Model.

Electrical Impedance Myography (EIM) is a noninvasive neurophysiologic technique to diagnose muscle health. Besides muscle properties, the EIM measurements vary significantly with the change of some other anatomic and nonanatomic factors such as skin fat thickness, shape and thickness of muscle, and electrode size and spacing due to its noninvasive nature of measurement. In this study, genetic algorithm was applied along with finite element model of EIM as an optimization tool in order to figure out an optimized EIM electrode setup, which is less affected by these factors, specifically muscle thickness variation, but does not compromise EIM's ability to detect muscle diseases. The results obtained suggest that a particular arrangement of electrodes and minimization of electrode surface area to its practical limit can overcome the effect of undesired factors on EIM parameters to a larger extent.

The effect of subacute denervation on the electrical anisotropy of skeletal muscle: implications for clinical diagnostic testing.

OBJECTIVE: Applied electrical current flows preferentially along rather than across muscle fibers, a characteristic called anisotropy. In this study, we investigate the alteration in muscle anisotropy after denervation. METHODS: Eight adult male rats underwent sciatic nerve crush and the gastrocnemius was harvested from 1 to 2.5 weeks later. Muscle from 12 additional healthy rats was also obtained. Multifrequency electrical impedance measurements were made on the tissue and its conductivity and relative permittivity (i.e., its polarizability) calculated. Anisotropy of the tissue was determined by calculating conductivity and permittivity differences, subtracting transverse from longitudinal values. Muscle fiber and blood vessel quantification were also performed. RESULTS: The mean conductivity difference for sciatic crush animals was higher (p<0.05) than for the healthy animals across the frequency spectrum, due to a greater increase in longitudinal conductivity than in transverse conductivity. For example, at 10 kHz, the conductivity difference was 0.15S/m for healthy animals and 0.29 S/m for post-crush animals. Relative permittivity difference values, however, were similar between groups. There was a strong correlation of conductivity anisotropy to muscle fiber size but not to blood vessel area. CONCLUSIONS: Anisotropy of muscle conductivity increases markedly after subacute denervation injury. SIGNIFICANCE: This alteration in anisotropy has direct relevance to the clinical application of electrical impedance myography. We also speculate that it may impact other forms of diagnostic testing, including needle electromyography and magnetic resonance imaging.

Finite element analysis of electrical impedance myography in the rat hind limb.

Electrical impedance myography (EIM) is a form of muscle assessment based on the surface application of electrical current and measurement of the resulting voltages over a muscle group of interest. In order to better understand the effect of pathological change in muscle, EIM has recently been applied to the rat. In this study, a finite element model of EIM is presented for the rat hind limb which incorporates the detailed anatomy of the leg based on computerized tomographic imaging and conductivity and permittivity values obtained from the rat gastrocnemius muscle. In addition, the angular anisotropy of the biceps femoris muscle has been included. The model successfully predicts the recorded surface impedances measured with EIM.

Electrical characteristics of rat skeletal muscle in immaturity, adulthood and after sciatic nerve injury, and their relation to muscle fiber size.

Localized impedance methods can provide useful approaches for assessing neuromuscular disease. The mechanism of these impedance changes remains, however, uncertain. In order to begin to understand the relation of muscle pathology to surface impedance values, 8 immature rats, 12 mature rats and 8 mature rats that had undergone sciatic crush were killed. Measurement was made on tissue from the gastrocnemius muscle from each animal in an impedance cell, and the conductivity and relative permittivity of the tissue were calculated in both the longitudinal and transverse directions for frequencies of 2 kHz to 1 MHz. In addition, quantitative histological analysis was performed on the tissue. Significant elevations in transverse conductivity and transverse relative permittivity were found with animal growth, but longitudinal values showed no difference. After sciatic crush, both transverse and longitudinal conductivity increased significantly, with no change in the relative permittivity in either direction. The frequency dependence of the values also changed after nerve injury. In the healthy animals, there was a strong linear relation between measured conductivity and relative permittivity with cell area, but not for the sciatic crush animals. These results provide a first step toward developing a comprehensive understanding of how the electrical properties of muscle alter in neuromuscular disease states.

Electrical impedance myography at 50kHz in the rat: technique, reproducibility, and the effects of sciatic injury and recovery.

OBJECTIVE: To describe a refined technique for performing electrical impedance myography (EIM) in the rat and assess its reproducibility, long-term stability, and the effects of sciatic nerve injury. METHODS: EIM at 50kHz was performed on the gastrocnemius-soleus complex of the rat hind limb in 12 rats, followed from 6 weeks of age for up to 6 months. Eight additional rats underwent sciatic nerve crush and 6 underwent a sham procedure. RESULTS: The EIM variables of resistance, reactance and phase demonstrated substantial change with growth until approximately 14 weeks of age, at which point the measurements stabilized, giving mean values of 6.0+/-5.7Omega, 22.1+/-2.1Omega, and 16.5+/-1.1 degrees , respectively, at 16 weeks of age. Immediate reproducibility of technique was high with an intraclass correlation coefficient of 0.91 and higher for all three parameters. Sciatic crush produced marked reductions in the reactance and phase that reversed over a several week period. CONCLUSIONS: These results support that 50kHz EIM can be performed effectively in adult rat models of neuromuscular disease with a straightforward experimental technique and that it is sensitive to neurogenic injury. SIGNIFICANCE: EIM can serve as a new approach to the study of neuromuscular disease in the rat.

Nerve conduction topography in geriatric hand assessment.

Motor nerve conduction is a noninvasive clinical test used to diagnose nerve problems such as carpal tunnel syndrome or peripheral neuropathy. Current techniques use a single-site recording over a superficial muscle. This traditional approach does not account for the electrical contributions from the other muscles innervated by the nerve being stimulated, which need to be considered with thumb carpometacarpal (CMC) degenerative joint disease (DJD) because these electrical contributions may change the anatomic relationship of the thenar muscles. This study recorded from 15 sites over the thenar eminence during motor nerve conduction studies of the median nerve of 12 young subjects with normal thenar anatomy and 25 elderly subjects with thumb CMC DJD. The maximum compound muscle action potential (CMAP) values did not occur in the same electrode position for the two groups, and traditional single-site recording would have resulted in smaller amplitudes and longer latencies for the elderly than the values noted with the multiple-site recordings. This pilot study of nerve conduction topography mapping with multiple-site recording illustrates that single-site studies may be misleading and supports further exploration of multichannel grid electrodes for topographic display and analysis of the CMAP.