Validation of a portable EMG device to assess muscle activity during free-living situations.

Portable amplifiers that record electromyograms (EMGs) for longer than four hours are commonly priced over $20,000 USD. This cost, and the technical challenges associated with recording EMGs during free-living situations, typically restrict EMG use to laboratory settings. A low-cost system (µEMG; OT Bioelecttronica, 100€), using specialized concentric bipolar electrodes, has been developed specifically for free-living situations. The purpose of this study was to validate the µEMG system by comparing EMGs from µEMG with a laboratory-based alternative (Telemyo 900; Noraxon USA, Inc.). Surface EMGs from biceps brachii (BB) and tibialis anterior (TA) of ten subjects were recorded simultaneously with both systems as subjects performed maximal voluntary contractions (MVCs), submaximal contractions at 25%, 50%, and 75% MVC, seven simulated activities of daily living (ADLs), and >60min of simulated free-living inside the laboratory. In general, EMG parameters (e.g., average full-wave rectified EMG amplitude) derived from both systems were not significantly different for all outcome variables, except there were small differences across systems in baseline noise and absolute EMG amplitudes during MVCs. These results suggest that µEMG is a valid approach to the long-term recording of EMG.

Autologous minced muscle grafts: a tissue engineering therapy for the volumetric loss of skeletal muscle.

Volumetric muscle loss (VML) results in a large void deficient in the requisite materials for regeneration for which there is no definitive clinical standard of care. Autologous minced muscle grafts (MG), which contain the essential components for muscle regeneration, may embody an ideal tissue engineering therapy for VML. The purpose of this study was to determine if orthotopic transplantation of MG acutely after VML in the tibialis anterior muscle of male Lewis rats promotes functional tissue regeneration. Herein we report that over the first 16 wk postinjury, MG transplantation 1) promotes remarkable regeneration of innervated muscle fibers within the defect area (i.e., de novo muscle fiber regeneration); 2) reduced evidence of chronic injury in the remaining muscle mass compared with nonrepaired muscles following VML (i.e., transplantation attenuated chronically upregulated transforming growth factor-ß1 gene expression and the presence of centrally located nuclei in 30% of fibers observed in nonrepaired muscles); and 3) significantly improves net torque production (i.e., ∼55% of the functional deficit in nonrepaired muscles was restored). Additionally, voluntary wheel running was shown to reduce the heightened accumulation of extracellular matrix deposition observed within the regenerated tissue of MG-repaired sedentary rats 8 wk postinjury (collagen 1% area: sedentary vs. runner, ∼41 vs. 30%), which may have been the result of an augmented inflammatory response [i.e., M1 (CCR7) and M2 (CD163) macrophage expression was significantly greater in runner than sedentary MG-repaired muscles 2 wk postinjury]. These findings support further exploration of autologous minced MGs for the treatment of VML.

Hemodynamic changes in rat leg muscles during tourniquet-induced ischemia-reperfusion injury observed by near-infrared spectroscopy.

In this study, we hypothesized that non-invasive continuous wave near-infrared spectroscopy (CWNIRS) can determine the severity or reversibility of muscle damage due to ischemia/reperfusion (I/R), and the results will be highly correlated with those from physical examination and histological analysis. To test this hypothesis, we performed CWNIRS measurements on two groups of male Sprague-Dawley rats ( approximately 400 g) that underwent 2 h (n = 6) or 3 h (n = 7) of pneumatic tourniquet application (TKA). Tissue oxyhemoglobin [HbO(2)] and deoxyhemoglobin [Hb] concentration changes were monitored during the 2 h or 3 h of 250 mmHg TKA and for an additional 2 h post-TKA. Rats were euthanized 24 h post-TKA and examined for injury, edema and viability of muscles. Contralateral muscles served as controls for each animal. In both groups, [HbO(2)] dropped immediately, then gradually decreased further after TKA and then recovered once the tourniquet was released. However, releasing after 2 h of TKA caused [HbO(2)] to overshoot above the baseline during reperfusion while the 3 h group continued to have lower [HbO(2)] than baseline. We found a significant correlation between the elapsed time from tourniquet release to the first recovery peak of [HbO(2)] and the muscle weight ratio between tourniquet and contralateral limb muscles (R = 0.86). Hemodynamic patterns from non-invasive CWNIRS demonstrated significant differences between 2 h and 3 h I/R. The results demonstrate that CWNIRS may be useful as a non-invasive prognostic tool for conditions involving vascular compromise such as extremity compartment syndrome.

Suturing of lacerations of skeletal muscle.

Our aim was to compare the biomechanical properties of suturing methods to determine a better method for the repair of lacerated skeletal muscle. We tested Kessler stitches and the combination of Mason-Allen and perimeter stitches. Individual stitches were placed in the muscle belly of quadriceps femoris from a pig cadaver and were tensioned mechanically. The maximum loads and strains were measured and failure modes recorded. The mean load and strain for the Kessler stitches were significantly less than those for combination stitches. All five Kessler stitches tore out longitudinally from the muscle. All five combination stitches did not fail but successfully elongated. Our study has shown that the better method of repair for suturing muscle is the use of combination stitches.

Inter-species extrapolation of skin heating resulting from millimeter wave irradiation: modeling and experimental results.

This study reports measurements of the skin surface temperature elevations during localized irradiation (94 GHz) of three species: rat (irradiated on lower abdomen), rhesus monkey (posterior forelimb), and human (posterior forearm). Two exposure conditions were examined: prolonged, low power density microwaves (LPM) and short-term, high power density microwaves (HPM). Temperature histories were compared with calculations from a bio-heat transfer model. The mean peak surface temperature increase was approximately 7.0 degrees C for the short-term HPM exposures for all three species/locations, and 8.5 degrees C (monkey, human) to 10.5 degrees C (rat) for the longer-duration LPM exposures. The HPM temperature histories are in close agreement with a one-dimensional conduction heat transfer model with negligible blood flow. The LPM temperature histories were compared with calculations from the bio-heat model, evaluated for various (constant) blood flow rates. Results suggest a variable blood flow model, reflecting a dynamic thermoregulatory response, may be more suited to describing skin surface temperature response under long-duration MMW irradiation.

Empirical validation of SAR values predicted by FDTD modeling.

Rapid increase in the use of numerical techniques to predict current density or specific absorption rate (SAR) in sophisticated three dimensional anatomical computer models of man and animals has resulted in the need to understand how numerical solutions of the complex electrodynamics equations match with empirical measurements. This aspect is particularly important because different numerical codes and computer models are used in research settings as a guide in designing clinical devices, telecommunication systems, and safety standards. To ensure compliance with safety guidelines during equipment design, manufacturing and maintenance, realistic and accurate models could be used as a bridge between empirical data and actual exposure conditions. Before these tools are transitioned into the hands of health safety officers and system designers, their accuracy and limitations must be verified under a variety of exposure conditions using available analytical and empirical dosimetry techniques. In this paper, empirical validation of SAR values predicted by finite difference time domain (FDTD) numerical code on sphere and rat is presented. The results of this study show a good agreement between empirical and theoretical methods and, thus, offer a relatively high confidence in SAR predictions obtained from digital anatomical models based on the FDTD numerical code.

Lack of effect of 94 GHz radio frequency radiation exposure in an animal model of skin carcinogenesis.

Although there is no evidence that electromagnetic energy in the radio frequency radiation (RFR) band is mutagenic, there have been suggestions that RFR energy might serve as either a promoter or co-promoter in some animal models of carcinogenesis. Recent developments in electromagnetic technology have resulted in the manufacture of RFR sources capable of generating frequencies in the millimeter wavelength (MMW) range (30-300 GHz). Because absorption of MMW energy occurs in the skin, it is to be expected that long-term detrimental health effects, if any, would most likely be manifest in the skin. In this study we investigated whether a single (1.0 W/cm(2) for 10 s) or repeated (2 exposures/week for 12 weeks, 333 mW/cm(2) for 10 s) exposure to 94 GHz RFR serves as a promoter or co-promoter in the 7,12-dimethylbenz[a]anthracene (DMBA)-induced SENCAR mouse model of skin carcinogenesis. Neither paradigm of MMW exposure significantly affected papilloma development, as evidenced by a lack of effect on tumor incidence and multiplicity. There was also no evidence that MMW exposure served as a co-promoter in DMBA-induced animals repeatedly treated with 12-O-tetradecanoylphorbol 13-acetate. Therefore, we conclude that exposure to 94 GHz RFR under these conditions does not promote or co-promote papilloma development in this animal model of skin carcinogenesis.

Predicted SAR in Sprague-Dawley rat as a function of permittivity values.

Specific absorption rate (SAR) value is dependent on permittivity value. However, variability in the published permittivity values for human and animal tissue and the development of sophisticated 3-dimensional digital anatomical models to predict SAR values has resulted in the need to understand how model parameters (permittivity value) affect the predicted whole body and localized SAR values. In this paper, we establish the partial derivative of whole body SARs and localized SAR values (defined as SAR for individual organs with respect to a change in the permittivity values of all tissue types, as well as for those tissues with the most variable permittivity values. Variations in the published permittivity values may substantially influence whole body and localized SAR values, but only under special conditions. Orientation of the exposed object to the incident electromagnetic wave is one of the most crucial factors. Published 2001 Wiley-Liss, Inc.

Regional distribution of Hsp70 in the CNS of young and old food-restricted rats following hyperthermia.

We examined the effect of aging on the capacity of the brain to produce heat shock protein (Hsp70) in response to heat stress, using high-powered microwaves (HPM, 2.06 GHz, 2.2 W/cm(2)) to induce hyperthermia for periods so brief that thermoregulatory factors were functionally eliminated as confounding variables. Unanesthetized young (6 months) and old (25 months) male, food-restricted Sprague-Dawley rats were exposed to HPM to induce a mean peak tympanic temperature (T(ty)) of 42.2 degrees C within 30 s. T(ty) returned to <40.0 degrees C within 6 min post-exposure in both age groups. Rats were euthanized 6 or 24 h later for immunohistochemical determination of Hsp70 accumulation in 10 brain regions. HPM exposure induced significant increases in 7 of the 10 regions. There were no significant differences observed in the pattern or density of Hsp70 accumulation between the young and old rats at 6 h post-HPM exposure, with the exception of the medial vestibular nucleus, which demonstrated significantly greater Hsp70 accumulation in the old rats. There were significant differences between the age groups at 24 h post-exposure, however, there was no general pattern; i.e., depending on the brain region, aged rats displayed significantly greater, lesser, or similar increases in Hsp70 expression compared with young. Taken together, these results demonstrate that the brain of aged, food-restricted rats does not display a loss of capacity to accumulate Hsp70 in response to heat stress.

Exercise in the heat is limited by a critical internal temperature.

We examined whether fatigue during exertional heat stress occurred at a critical internal temperature independent of the initial temperature at the start of exercise. Microwaves (2.1 GHz; 100 mW/cm(2)) were used to rapidly (3-8 min) heat rats before treadmill exercise to exhaustion. In a repeated-measures design, food-restricted male Sprague-Dawley rats (n = 11) were preheated to three levels (low, medium, and high). In addition, two sham exposures, Sham 1 and Sham 2, were administered at the beginning and end of the study, respectively. At the initiation of exercise, hypothalamic (T(hyp)) and rectal (T(rec)) temperatures ranged from 39.0 degrees C to 42.8 degrees C (T(hyp)) and 42.1 degrees C (T(rec)). The treadmill speed was 17 m/min (8 degrees grade), and the ambient temperature during exercise was 35 degrees C. Each treatment was separated by 3 wk. Run time to exhaustion was significantly reduced after preheating. There was a significant negative correlation between run time and initial T(hyp) and T(rec) (r = 0.73 and 0.74, respectively). The temperatures at exhaustion were not significantly different across treatments, with a range of 41.9-42.2 degrees C (T(hyp)) and 42.2-42.5 degrees C (T(rec)). There were no significant differences in run time in the sham runs administered at the start and end of the investigation. No rats died as a result of exposure to any of the treatments, and body weight the day after each treatment was unaffected. These results support the concept that a critical temperature exists that limits exercise in the heat.

Heating and pain sensation produced in human skin by millimeter waves: comparison to a simple thermal model.

Cutaneous thresholds for thermal pain were measured in 10 human subjects during 3-s exposures at 94 GHz continuous wave microwave energy at intensities up to approximately 1.8 W cm(-2). During each exposure, the temperature increase at the skin's surface was measured by infrared thermography. The mean (+/- s.e.m.) baseline temperature of the skin was 34.0+/-0.2 degrees C. The threshold for pricking pain was 43.9+/-0.7 degrees C, which corresponded to an increase in surface temperature of approximately 9.9 degrees C (from 34.0 degrees C to 43.9 degrees C). The measured increases in surface temperature were in good agreement with a simple thermal model that accounted for heat conduction and for the penetration depth of the microwave energy into tissue. Taken together, these results support the use of the model for predicting thresholds of thermal pain at other millimeter wave (length) frequencies.

Regional brain heating during microwave exposure (2.06 GHz), warm-water immersion, environmental heating and exercise.

Nonuniform heating may result from microwave (MW) irradiation of tissues and is therefore important to investigate in terms of health and safety issues. Hypothalamic (Thyp), cortical (Tctx), tympanic (Tty), and rectal (Tre) temperatures were measured in rats exposed in the far field, k-polarization (i.e., head pointed toward the transmitter horn and E-field in vertical direction) to two power densities of 2.06 GHz irradiation. The high-power density (HPM) was 1700 mW/cm2 [specific absorption rate (SAR): hypothalamus 1224 W/kg; cortex 493 W/kg]; the low-power density (LPM) was 170 mW/cm2 (SAR: hypothalamus 122.4 W/kg; cortex 49.3 W/kg). The increase (rate-of-rise, in degrees C/s) in Thyp was significantly greater than those in Tctx or Tre when rats were exposed to HPM. LPM produced more homogeneous heating. Quantitatively similar results were observed whether rats were implanted with probes in two brain sites or a single probe in one or the other of the two sites. The qualitative difference between regional brain heating was maintained during unrestrained exposure to HPM in the h-polarization (i.e., body parallel to magnetic field). To compare the temperature changes during MW irradiation with those produced by other modalities of heating, rats were immersed in warm water (44 degrees C, WWI); exposed to a warm ambient environment (50 degrees C, WSED); or exercised on a treadmill (17 m/min 8% grade) in a warm ambient environment (35 degrees C, WEX). WWI produced uniform heating in the regions measured. Similar rates-of-rise occurred among regions following WSED or WEX, thus maintaining the pre-existing gradient between Thyp and Tctx These data indicate that HPM produced a 2-2.5-fold difference in the rate-of-heating within brain regions that were separated by only a few millimeters. In contrast, more homogeneous heating was recorded during LPM or nonmicrowave modalities of heating.

HSP70 expression in the CNS in response to exercise and heat stress in rats.

We have previously documented the regional distribution of 70-kDa heat shock protein (HSP70) in brains of rats made hyperthermic by brief exposure to high-powered microwaves (HPM; 2.06 GHz). We now compare HSP70 expression induced by HPM exposure to that induced by exertional and/or environmental heat stress. Rats were chronically implanted with a temperature probe guide in the hypothalamic region of the brain (Tbr). After recovery, the following treatment groups were examined: HPM; sham exposed; treadmill exercise at room temperature (24 degreesC; Ex-1); treadmill exercise in a warm environment (34 degreesC; Ex-2); and sedentary groups (Sed-1 and Sed-2), in which ambient temperature was adjusted so that the Tbr mimicked the Tbr in the corresponding exercise groups. Significant HSP70 expression occurred only in the hyperthermic (Ex-2, Sed-2, and HPM) groups. The pattern of HSP70 expression was similar among Ex-2 and Sed-2 rats but differed from that in HPM rats. We conclude that 1) the pattern of HSP70 expression differs between HPM and nonmicrowave heating, and 2) exercise alone was not sufficient to induce central HSP70 expression.

Age does not affect thermal and cardiorespiratory responses to microwave heating in calorically restricted rats.

This study sought to determine whether age influences the thermal distribution and cardiorespiratory responses to 35 GHz microwave (MW) heating. Male Sprague-Dawley rats (n = 8/group) 3 to 4 mo old (young), 15 to 16 mo old (middle-aged), and 24 to 25 mo old (old) were used. All animals were restricted to 63% of ad libitum feed. Rats were anesthetized (ketamine) and a catheter was placed into a carotid artery for measurement of mean arterial blood pressure (MAP). Anesthetized rats were then exposed to MWs until death, while measuring MAP, heart rate and temperatures at five sites (colonic, left and right tympanic, subcutaneous, and tail). Before MW exposure, there were no significant (p < .05) differences among age groups in measured parameters. MW produced increases in temperature at each of the measured sites; temperatures at death did not differ between groups. Heart rate increased throughout MW exposure, in a statistically identical manner in all age groups. MAP was initially well maintained and then, in the latter phases of heating, precipitously declined until death, with no discernible age-related difference. Respiration rate was not altered by MW exposure in any group. Finally, there were no group differences in the MW exposure time required to induce death. Thus, age does not alter thermal and cardiorespiratory responses to 35 GHz MW heating in food-restricted rats.

Uncoupling of changes in skeletal muscle beta-adrenergic receptor density and aerobic capacity during the aging process.

The results of the present study indicate that the density of the beta-adrenergic receptors in the skeletal muscle does not decline with age, despite declines in oxidative capacity both in the skeletal muscle and whole body oxygen consumption. When young rats and old rats of equal body weight trained daily at the same duration and speed for 6 months on the treadmill, skeletal muscle of young and old rats reached the same aerobic capacity. The young demonstrated a significant rise in Bmax of the beta receptors, while the old rats did not change their density of receptors. When both young and old rats had the contractile activity of their skeletal muscle raised to the same level through chronic tonic electrical stimulation, the aerobic-capacity and beta receptor density rose to the same levels in the skeletal muscle. Thus, the contraction-dependent pathway in the senescent muscle appears to function normally given a maximal chronic stimulus via electrical stimulation. These data indicate that the relationship between oxidative capacity, beta-adrenergic receptor properties, exercise training, and aging does not appear to be readily explicable by a single unifying mechanism, but probably resides in the interaction of age with a differential responsiveness of the beta-adrenergic and/or contraction dependent pathway for stimulation of aerobic capacity in the aging skeletal muscle.

Thresholds of microwave-evoked warmth sensations in human skin.

We measured thresholds for microwave-evoked skin sensations of warmth at frequencies of 2.45, 7.5, 10, 35, and 94 GHz. In the same subjects, thresholds of warmth evoked by infrared radiation (IR) were also measured for comparison. Detection thresholds were measured on the skin in the middle of the back in 15 adult male human subjects at all microwave (MW) frequencies and with IR. Long duration (10-s), large area (327-cm2) stimuli were used to minimize any differential effects of temporal or spatial summation. Sensitivity increased monotonically with frequency throughout the range of microwave frequencies tested. The threshold at 94 GHz (4.5 +/- 0.6 mW/cm2) was more than an order of magnitude less than at 2.45 GHz (63.1 +/- 6.7 mW/cm2), and it was comparable to the threshold for IR (5.34 +/- 1.07 mW/cm2).

Deployment telemedicine: the Walter Reed Army Medical Center experience.

This retrospective study analyzed telemedicine consultations from deployed military medical units in Somalia, Haiti, Croatia, and Macedonia to determine the clinical utility of telemedicine consultations. A computerized data-collection sheet was developed and information was abstracted from consultation requests and consultant replies. Questions relating to the consultation request include basic patient demographics, the deployed physician's specialty, questions asked, consultation urgency, specialties requested by the consultation, type of equipment used, history of present illness, and differential diagnosis. Data extracted from the consultant's reply were the consultant's diagnosis and recommendations. Subjective questions included the severity of illness and the degree to which telemedicine affected the diagnosis, treatment, or patient status. Results show that physicians in many different specialties employed telemedicine consultations in a wide range of patients and illnesses. Telemedicine consultations significantly affected the diagnosis in 30%, the treatment in 32%, and the overall patient status in 70% of cases.

Lack of behavioral effects in non-human primates after exposure to ultrawideband electromagnetic radiation in the microwave frequency range.

The effect of acute exposure to ultrawideband (UWB) electromagnetic radiation on the Primate Equilibrium Platform (PEP) task, where the monkey's task is to manipulate a joystick control to compensate for the random perturbations in the pitch plane that are generated by a computer at unpredictable intervals, was examined. The duration of the UWB exposure was 2 min at a pulse repetition rate of 60 Hz (total of 7200 pulses). The bandwidth of the pulse was 100 MHz to 1.5 GHz (peak power between 250-500 MHz) with a peak E-field strength of 250 kV/m. Each monkey was exposed twice. The interval between exposures was 6 days. The exposure to UWB electromagnetic radiation had no effect on PEP performance when tested immediately after exposure.

No detectable bioeffects following acute exposure to high peak power ultra-wide band electromagnetic radiation in rats.

A wide range assessment of the possible bioeffects of an acute exposure to high peak power ultra-wide band (UWB) electromagnetic radiation was performed in rats. The UWB-exposure consisted of 2 min of pulsed (frequency: 60 Hz, pulse width: 5-10 ns) UWB (bandwidth: 0.25-2.50 GHz) electromagnetic radiation. Rats were examined using one of the following: 1) a functional observational battery (FOB); 2) a swimming performance test; 3) a complete panel of blood chemistries; or 4) determination of the expression of the c-fos protein in immunohistologically-stained sections of the brain. No significant differences were found between UWB- or sham-exposed rats on any of the measured parameters.

Database created from magnetic resonance images of a Sprague-Dawley rat, rhesus monkey, and pigmy goat.

To obtain a database of accurate anatomical images onto which dosimetry data of electromagnetic fields could be mapped, a healthy Sprague-Dawley rat, rhesus monkey, and pigmy goat were scanned using magnetic resonance imaging (MRI). Axial sections throughout the length of the animals were collected. Sections were 3 mm thick for the rat and 5 mm thick for the monkey and goat. Sagittal sections (2 mm thick) of the rat head were also scanned. Images were recorded on magnetic tape and transferred to computer disk for image enhancement and network distribution. Images are available in 16 bit Big Endian signed or 8 bit TIFF formats. This is the first database of contiguous MRI axial scans of rat, monkey, and goat available for distribution via magnetic tape (4 mm DDS) or Internet file transfer protocol. Digital transfer of the data was selected to preserve the integrity of each image, circumventing the need for the user to scan the images back into a digital format for use with their software. These images should be useful to physiologists, neuroscientists, veterinarians, anatomists, and teachers. Reconstructing these 2-dimensional images into 3-dimensional structures is an effective media for conveying spatial anatomical information in a quick and comprehensive manner.