The effect of photobiomodulation on histamine and Mucuna pruriens-induced pruritus, hyperknesis and alloknesis in healthy volunteers: A double-blind, randomized, sham-controlled study.

BACKGROUND: Photobiomodulation, also referred to as Low-Level Light Therapy (LLLT), has emerged as a promising intervention for pruritus, a prevalent and often distressing symptom. OBJECTIVES: This study investigated the efficacy of low-level light therapy (LLLT) in alleviating pruritus, hyperknesis, and alloknesis induced by histamine and Mucuna pruriens. METHODS: In a double-blind, randomized, sham-controlled trial with a split-body design, healthy volunteers underwent 6 minutes of LLLT and sham treatments in separate upper back quadrants. The histamine model was applied to the upper quadrants, and Mucuna pruriens to the lower quadrants. Pruritus intensity, alloknesis, hyperknesis, flare area, and skin temperature were measured pre and post treatment. RESULTS: Seventeen individuals (eight females, nine males) participated in the study. In the histamine model, LLLT notably reduced itch intensity (difference = 13.9 (95% CI: 10.5 - 17.4), p = 0.001), alloknesis (difference = 0.80 (95% CI: 0.58-1.02), p = 0.001), and hyperknesis (difference = 0.48 (95% CI: 0.09-0.86), p = 0.01). Skin temperature changes were not significantly different between the two groups (difference = -2.0 (95% CI: -6.7-2.6), p = 0.37). For the Mucuna pruriens model, no significant differences were observed in any measures, including itch intensity (difference = 0.8 (95% CI: -2.3 - 3.8), p = 0.61) hyperknesis (difference = 0.08 (95% CI: -0.06-0.33), p = 0.16) and alloknesis (difference = 0. 0.09 (95% CI: -0.08-0.256), p = 0.27). CONCLUSIONS: LLLT effectively reduced histamine-induced pruritus, alloknesis, and hyperknesis; however, LLLT was ineffective against Mucuna pruriens-induced pruritus. Further investigations are required to determine LLLT's effectiveness of LLLT in various pruritus models.

Evaluation of Non-invasive Fat Reduction Using a Resistive Electric Transfer-based Radiofrequency Device With Multi-channel Handpieces.

BACKGROUND/AIM: Various devices for non-invasive body shape correction are being developed along with the growth of the beauty industry. Radiofrequency (RF) can selectively reduce subcutaneous fat without causing skin damage. The efficacy of the procedure can be improved by applying RF to a large area simultaneously with multiple handpieces. This study evaluated the safety and efficacy of a new RF device with multi-channel handpieces. MATERIALS AND METHODS: In ex vivo experiments, the RF device was used to treat porcine tissue comprising the skin, subcutaneous, and muscle layers. The device's safety was evaluated by temperature measurements of porcine tissue and histological analysis. In in vivo experiments, the dorsal skin of pigs was treated with the RF device. The safety and efficacy of the device were evaluated by measuring the skin temperature, subcutaneous fat layer thickness, and conducting histological analysis. RESULTS: The skin temperature did not exceed the set temperature during treatment, and skin damage was not observed in histologic analysis in both ex vivo and in vivo experiments. In in vivo experiments, the subcutaneous fat layer thickness and subcutaneous lipocyte size were decreased after treatment. In addition, the fibrous tissue between subcutaneous lipocytes was increased in the RF treatment group compared with the non-treatment group. CONCLUSION: The RF device used in this study effectively reduced the size of subcutaneous lipocytes and increased fibrous tissue without skin damage. Therefore, the safe and effective use of this device for non-invasive fat reduction may be possible in clinical settings.

The effectiveness of far-infrared irradiation on foot skin surface temperature and heart rate variability in healthy adults over 50 years of age: A randomized study.

BACKGROUND: Far-infrared irradiation (FIR) is used in the medical field to improve wound healing, hemodialysis with peripheral artery occlusive disease, and osteoarthritis but seldom used in ameliorating poor lower extremity circulation. The purpose of this study was to evaluate the effect of FIR on changes in foot skin surface temperature (FSST) and autonomic nerve system (ANS) activity to evaluate its effectiveness in improving lower limb circulation. METHODS: A randomized controlled study was conducted. Subjects (n = 44), all over the age of 50 years and satisfying the inclusion criteria, were randomly allocated into 2 groups. The intervention group received FIR on a lower limb for 40 minutes and the control group received no intervention. Left big toe (LBT), right big toe (RBT), left foot dorsal (LFD), right foot dorsal (RFD) surface skin temperature, autonomic nervous activity, and blood pressure were assessed. RESULTS: The main results were skin surface temperature at the LBT increased from 30.8 ±â€Š0.4°C to 34.8 ±â€Š0.4°C, at RBT increased from 29.6 ±â€Š0.4°C to 35.3 ±â€Š0.4°C and LFD increased from 31.9 ±â€Š0.3°C to 36.4 ±â€Š0.4°C, RFD increased from 30.7 ±â€Š0.3°C to 37.7 ±â€Š0.2°C. FIR caused a significant increase of the FSST ranging in a 4°C to 7°C increase after 40 minutes irradiation (P < .001). The ANS low-frequency (LF) and high-frequency (HF) activity showed a statistically significant increase in the FIR group (P < .05) but not the LF/HF ratio. CONCLUSION: FIR significantly increased the FSST from between 4°C and 7°C after 40 minutes irradiation, which might improve lower extremity circulation and regulation of ANS activity.

Effect of Radiofrequency Electromagnetic Fields on Thermal Sensitivity in the Rat.

The World Health Organization and the French Health Safety Agency (ANSES) recognize that the expressed pain and suffering of electromagnetic field hypersensitivity syndrome (EHS) people are a lived reality requiring daily life adaptations to cope. Mechanisms involving glutamatergic N-methyl d-aspartate (NMDA) receptors were not explored yet, despite their possible role in hypersensitivity to chemicals. Here, we hypothesized that radiofrequency electromagnetic field (RF-EMF) exposures may affect pain perception under a modulatory role played by the NMDA receptor. The rats were exposed to RF-EMF for four weeks (five times a week, at 0 (sham), 1.5 or 6 W/kg in restraint) or were cage controls (CC). Once a week, they received an NMDA or saline injection before being scored for their preference between two plates in the two-temperatures choice test: 50 °C (thermal nociception) versus 28 °C. Results in the CC and the sham rats indicated that latency to escape from heat was significantly reduced by -45% after NMDA, compared to saline treatment. Heat avoidance was significantly increased by +40% in the 6 W/kg, compared to the sham exposed groups. RF-EMF effect was abolished after NMDA treatment. In conclusion, heat avoidance was higher after high brain-averaged specific absorption rate, affording further support for possible effect of RF-EMF on pain perception. Further studies need to be performed to confirm these data.

Effects of Contrast Therapy Using Infrared and Cryotherapy as Compared with Contrast Bath Therapy on Blood Flow, Muscle Tone, and Pain Threshold in Young Healthy Adults.

BACKGROUND The aim of this research was to compare the effects of contrast bath therapy (CBT) and contrast therapy (CT) using infrared (IR) and cryotherapy (CR) on blood flow, muscle tone, and pain in the forearm. MATERIAL AND METHODS Twenty healthy individuals participated in this study. Each participant received 2 kinds of CT separated by a week. CBT involved immersion in hot water (38-40°C) for 4 minutes, followed by 1 minute of immersion in cold water (12-14°C) for four rotations. CT using IR and CR was performed in the same manner as CBT. RESULTS The variables measured were blood flow, muscle tone, and pain before and after intervention. Both types of CT produced fluctuations in the blood flow (P<0.05). The pain threshold increased on both therapies; a significant increase was noted with IR and CR (P<0.05) therapies. Muscle elasticity was induced and stiffness was reduced with all therapies (P<0.05). IR and CR resulted in significant changes (P<0.05) in blood flow as compared with the CBT. CONCLUSIONS The results of this study suggest that CT using IR and CR is more effective in improving blood flow than CBT and has the same effect on muscle tone and pain. Nonetheless, using IR and CR is efficient with regard to mobility and maintaining temperature; therefore, it would be convenient to use these in clinical settings. Further studies involving CT should be carried out to determine whether our findings are clinically relevant.

Quantitative Thermal Imaging Biomarkers to Detect Acute Skin Toxicity From Breast Radiation Therapy Using Supervised Machine Learning.

PURPOSE: Radiation-induced dermatitis is a common side effect of breast radiation therapy (RT). Current methods to evaluate breast skin toxicity include clinical examination, visual inspection, and patient-reported symptoms. Physiological changes associated with radiation-induced dermatitis, such as inflammation, may also increase body-surface temperature, which can be detected by thermal imaging. Quantitative thermal imaging markers were identified and used in supervised machine learning to develop a predictive model for radiation dermatitis. METHODS AND MATERIALS: Ninety patients treated for adjuvant whole-breast RT (4250 cGy/fx = 16) were recruited for the study. Thermal images of the treated breast were taken at 4 intervals: before RT, then weekly at fx = 5, fx = 10, and fx = 15. Parametric thermograms were analyzed and yielded 26 thermal-based features that included surface temperature (°C) and texture parameters obtained from (1) gray-level co-occurrence matrix, (2) gray-level run-length matrix, and (3) neighborhood gray-tone difference matrix. Skin toxicity was evaluated at the end of RT using the Common Terminology Criteria for Adverse Events (CTCAE) guidelines (Ver.5). Binary group classes were labeled according to a CTCAE cut-off score of ≥2, and thermal features obtained at fx = 5 were used for supervised machine learning to predict skin toxicity. The data set was partitioned for model training, independent testing, and validation. Fifteen patients (∼17% of the whole data set) were randomly selected as an unseen test data set, and 75 patients (∼83% of the whole data set) were used for training and validation of the model. A random forest classifier with leave-1-patient-out cross-validation was employed for modeling single and hybrid parameters. The model performance was reported using receiver operating characteristic analysis on patients from an independent test set. RESULTS: Thirty-seven patients presented with adverse skin effects, denoted by a CTCAE score ≥2, and had significantly higher local increases in skin temperature, reaching 36.06°C at fx = 10 (P = .029). However, machine-learning models demonstrated early thermal signals associated with skin toxicity after the fifth RT fraction. The cross-validated model showed high prediction accuracy on the independent test data (test accuracy = 0.87) at fx = 5 for predicting skin toxicity at the end of RT. CONCLUSIONS: Early thermal markers after 5 fractions of RT are predictive of radiation-induced skin toxicity in breast RT.

Does the Application of Tecar Therapy Affect Temperature and Perfusion of Skin and Muscle Microcirculation? A Pilot Feasibility Study on Healthy Subjects.

Background: Tecar therapy (TT) is an endogenous thermotherapy used to generate warming up of superficial and deep tissues. TT capability to affect the blood flow is commonly considered to be the primary mechanism to promote tissue healing processes. Despite some preliminary evidence about its clinical efficacy, knowledge on the physiologic responses induced by TT is lacking. Objective: The aim of this quantitative randomized pilot study was to determinate if TT, delivered in two modes (resistive and capacitive), affects the perfusion of the skin microcirculation (PSMC) and intramuscular blood flow (IMBF). Design: A randomized controlled pilot feasibility study. Subjects: Ten healthy volunteers (n = 4 females, n = 6 males; mean age 35.9 ± 10.7 years) from a university population were recruited and completed the study. Intervention: All subjects received three different TT applications (resistive, capacitive, and placebo) for a period of 8 min. Outcome measures: PSMC, IMBF, and the skin temperature (ST) were measured pre- and post-TT application using power Doppler sonography, laser speckle contrast imaging (LSCI), and infrared thermography. Results: Compared with placebo application, statistically significant differences in PSMC resulted after both the resistive (p = 0.0001) and the capacitive (p = 0.0001) TT applications, while only the resistive modality compared with the placebo was capable to induce a significant change of IMBF (p = 0.013) and ST (p = 0.0001). Conclusions: The use of power Doppler sonography and LSCI enabled us to evaluate differences in PSMC and IMBF induced by TT application.

Relationships between the changes of skin temperature and radiation skin injury.

Background: Radiation skin injury (RSI) causes changes in skin temperature, but detailed information on the thermographic responses is currently lacking. We investigated thermographic patterns after radiotherapy. We hypothesized that skin temperature may be used as a diagnostic and early predictor of RSI severity.Method: All breast cancer patients received radiotherapy after unilateral postmastectomy. The contralateral supraclavicular area served as control, and the frontal thermal image of torso was taken by a thermal infrared imager weekly. We defined areas of interest on bilateral symmetrical supraclavicular area, and analyzed the difference of average and maximum skin temperature (DSTaverage and DSTmax) between them. The extent of the weekly variation in DST (DSTW) was calculated using a mathematical formula to represent a trend of skin temperature change. RSI and symptoms related to RSI were scored from baseline to 2 weeks after the end of radiotherapy.Results: Forty-one patients were enrolled in this study. In comparison to the baseline, the DSTaverage and DSTmax increased significantly over time during radiotherapy (p < .05). The onset of DST increase was accompanied by the onset of radiation dermatitis, and the maximal DST also appeared at the peak of Radiation Therapy Oncology Group (RTOG) and symptom scores. Radiation dose, DSTaverage, burning-feeling and pulling were the independent variables affecting RTOG score according to multivariate analysis (p < .001, p < .034, p < .001, p < .001). Patients with DSTWaverage >1.223 or DSTWmax >1.114 in second week showed a late higher dermatitis score (RTOG score ≥2).Conclusion: This study confirmed that RSI was associated with thermographic response. Our results suggested that the follow-up observations of skin temperature during radiotherapy could provide the objective evaluation criteria and prediction methods for RSI.

Infrared-Radiation-Enhanced Nanofiber Membrane for Sky Radiative Cooling of the Human Body.

Extreme heat events are mainly responsible for weather-related human mortality due to climate change. However, there is a lack of outdoor thermal management for protecting people from extreme heat events. We present a novel infrared-radiation-enhanced nanofiber membrane (NFM) that has good infrared resonance absorption and selectively radiates thermal radiation of the human body through the atmosphere and into the cold outer space. The NFM comprises polyamide 6 (PA6) nanofibers and randomly distributed SiO2 submicron spheres and has sufficient air permeability and thermal-moisture comfortability because of its interconnect nanopores and micropores. We measure the sky radiative cooling performance under a clear sky, and PA6/SiO2 NFM produces temperatures that are about 0.4-1.7 °C lower than those of commercial textiles when covering dry and wet hands and temperatures 1.0-2.5 °C lower than the ambient temperature when thermal conduction and convection are isolated in a closed device. Our processed PA6/SiO2 NFM combines sky radiative cooling with thermal management of the human body very well, which will promote the development of radiative cooling textiles.

Active compound chrysophanol of Cassia tora seeds suppresses heat-induced lipogenesis via inactivation of JNK/p38 MAPK signaling in human sebocytes.

BACKGROUND: Heat induced by infrared (IR) radiation from sun exposure increases skin temperature and can lead to thermal and photo-aging. However, little is known about the relationship between heat induced by IR radiation and lipid biosynthesis in human sebocytes. This study investigated the expression of factors involved in lipid biosynthesis in human sebocytes exposed to heat. The effect of Cassia tora extract and chrysophanol, which is widely used as anti-inflammatory agent, on the heat shock effect in sebocytes was then examined. METHODS: For the treatment, cells were maintained in culture medium without FBS (i.e., serum starved) for 6 h and then moved for 30 min to incubators at 37 °C (control), 41 °C, or 44 °C (heat shock). Culture media were replaced with fresh media without FBS. To investigate expression of gene and signaling pathway, we performed western blotting. Lipid levels were assessed by Nile red staining. The cytokine levels were measured by cytokine array and ELISA kit. RESULTS: We found that peroxisome proliferator-activated receptor (PPAR)γ and fatty acid synthase (FAS) were upregulated and the c-Jun N-terminal kinase (JNK)/p38 signaling pathways were activated in human sebocytes following heat exposure. Treatment with Cassia tora seed extract and chrysophanol suppressed this up-regulation of PPARγ and FAS and also suppressed the increase in IL-1ß levels. CONCLUSION: These findings provide evidence that IR radiation can stimulate sebum production; Cassia tora seed extract and chrysophanol can reverse lipid stimulated inflammatory mediation, and may therefore be useful for treating skin disorders such as acne vulgaris.

Radiofrequency Electromagnetic Field Exposure and the Resting EEG: Exploring the Thermal Mechanism Hypothesis.

There is now strong evidence that radiofrequency electromagnetic field (RF-EMF) exposure influences the human electroencephalogram (EEG). While effects on the alpha band of the resting EEG have been repeatedly shown, the mechanisms underlying that effect have not been established. The current study used well-controlled methods to assess the RF-EMF exposure effect on the EEG and determine whether that effect might be thermally mediated. Thirty-six healthy adults participated in a randomized, double-blind, counterbalanced provocation study. A water-perfusion suit (34 C) was worn throughout the study to negate environmental influences and stabilize skin temperature. Participants attended the laboratory on four occasions, the first being a calibration session and the three subsequent ones being exposure sessions. During each exposure session, EEG and skin temperature (8 sites) were recorded continuously during a baseline phase, and then during a 30 min exposure to a 920 MHz GSM-like signal (Sham, Low RF-EMF (1 W/kg) and High RF-EMF (2 W/kg)). Consistent with previous research, alpha EEG activity increased during the High exposure condition compared to the Sham condition. As a measure of thermoregulatory activation, finger temperature was found to be higher during both exposure conditions compared to the Sham condition, indicating for the first time that the effect on the EEG is accompanied by thermoregulatory changes and suggesting that the effect of RF-EMF on the EEG is consistent with a thermal mechanism.

Besides Photothermal Effects, Low-Level CO2 Laser Irradiation Can Potentiate Skin Microcirculation Through Photobiomodulation Mechanisms.

Background: Improvement of microcirculation is one of the important mechanisms of low-level laser therapy (LLLT) to treat some diseases such as wound healing. Most previous studies have been carried out with multiple lasers other than the 10,600-nm CO2 laser. Recently, the CO2 laser has been used not only as a tool for excision of soft tissues but also for therapeutic applications. Objective: To study whether low-level CO2 laser irradiation can influence microcirculation and further explore the underlying mechanisms. Methods: Seventy-milliwatt (70-mW) CO2 lasers irradiated the forearms of 12 participants and skin blood perfusion (SkBP) was measured with a laser speckle imager. The thermal effect of irradiation was evaluated by measuring the irradiated skin in vivo and the exposed cell suspensions in vitro. Extracellular adenosine triphosphate (eATP) of the human mast cell line (HMC-1) is assessed by luciferin-luciferase assay to explore the potential mechanisms. Results: Irradiation caused dose-dependent increase in SkBP. At a medium dose of 262 J/cm2, SkBP reached its maximum value at 195.8% ± 18.6% of the baseline (n = 12, p < 0.01). Such laser irradiation had a mild thermal effect, heating local skin temperature (SkT) by 6.1°C ± 0.3°C (n = 10) and warming cell suspensions by 4.5°C ± 0.8°C (n = 6). Irradiation dose-dependently lowered eATP levels of HMC-1 cells in vitro. At a medium dose of 262 J/cm2, eATP levels declined to the minimum at 74.8% ± 5.5% of the baseline (n = 12, p < 0.01). This downregulation effect could be significantly inhibited by 100-µM ARL67156, a nonspecific ecto-ATPase inhibitor. On the contrary, heating itself slightly raised the level of eATP. Conclusions: Low-level CO2 laser irradiation can improve microcirculation. Besides the thermal effect, regulation of extravascular eATP by the photobiomodulation mechanism may be involved. This implies that CO2 lasers might be used in LLLT.

Model of Steady-state Temperature Rise in Multilayer Tissues Due to Narrow-beam Millimeter-wave Radiofrequency Field Exposure.

The assessment of health effects due to localized exposures from radiofrequency fields is facilitated by characterizing the steady-state, surface temperature rise in tissue. A closed-form analytical model was developed that relates the steady-state, surface temperature rise in multilayer planar tissues as a function of the spatial-peak power density and beam dimensions of an incident millimeter wave. Model data was derived from finite-difference solutions of the Pennes bioheat transfer equation for both normal-incidence plane waves and for narrow, circularly symmetric beams with Gaussian intensity distribution on the surface. Monte Carlo techniques were employed by representing tissue layer thicknesses at different body sites as statistical distributions compiled from human data found in the literature. The finite-difference solutions were validated against analytical solutions of the bioheat equation for the plane wave case and against a narrow-beam solution performed using a commercial multiphysics simulation package. In both cases, agreement was within 1-2%. For a given frequency, the resulting analytical model has four input parameters, two of which are deterministic, describing the level of exposure (i.e., the spatial-peak power density and beam width). The remaining two are stochastic quantities, extracted from the Monte Carlo analyses. The analytical model is composed of relatively simple functions that can be programmed in a spreadsheet. Demonstration of the analytical model is provided in two examples: the calculation of spatial-peak power density vs. beam width that produces a predefined maximum steady-state surface temperature, and the performance evaluation of various proposed spatial-averaging areas for the incident power density.

Effects of Footbaths with Mustard, Ginger, or Warm Water Only on Objective and Subjective Warmth Distribution in Healthy Subjects: A Randomized Controlled Trial.

OBJECTIVE: To analyze the short-term thermogenic effects of footbaths with warm water alone (WA) versus when combined with medicinal powders. DESIGN: Randomized controlled trial with cross-over. INTERVENTIONS AND OUTCOMES: Seventeen healthy volunteers (mean age 22.1 years, SD = 2.4; 11 female) received three footbaths with WA or WA combined with mustard (MU) or ginger (GI) in a randomized order. Self-perceived warmth (Herdecke warmth perception questionnaire) and actual skin temperatures (thermography) were assessed before (t0), immediately after footbaths (t1), and 10 minutes later (t2). The primary outcome was perceived warmth in the feet. Secondary outcomes were warmth perception in the face, hands and overall, as well as actual skin temperature in the feet, face, and hands. RESULTS: Perceived warmth at the feet (primary outcome) increased significantly (all p's < .001) for MU and GI at t1 as well as for GI at t2 when compared to t0 with high effect sizes. At t2, GI differed significantly from WA (p < .001) and MU (p = .048). With regards to the secondary measures of outcome, no significant effects were seen for perceived warmth at the face or hands. Overall warmth was significantly higher at t1 compared to t0 (p = .01). Thermography assessments of skin temperature at the feet at t1 increased after all conditions (p < .001). No effects were seen in the face. At the hands, temperature decreased at t1 (p = .02) and t2 compared to t0 (p < .001). CONCLUSION: The present study provides preliminary evidence that mustard and ginger increase warmth perception at the feet more than warm water alone, with only the effects for GI enduring at the brief follow-up.

Comparison of Thermal Response for RF Exposure in Human and Rat Models.

In the international guidelines/standards for human protection against electromagnetic fields, the specific absorption rate (SAR) is used as a metric for radio-frequency field exposure. For radio-frequency near-field exposure, the peak value of the SAR averaged over 10 g of tissue is treated as a surrogate of the local temperature elevation for frequencies up to 3⁻10 GHz. The limit of 10-g SAR is derived by extrapolating the thermal damage in animal experiments. However, no reports discussed the difference between the time constant of temperature elevation in small animals and humans for local exposure. This study computationally estimated the thermal time constants of temperature elevation in human head and rat models exposed to dipole antennas at 3⁻10 GHz. The peak temperature elevation in the human brain was lower than that in the rat model, mainly because of difference in depth from the scalp. Consequently, the thermal time constant of the rat brain was smaller than that of the human brain. Additionally, the thermal time constant in human skin decreased with increasing frequency, which was mainly characterized by the effective SAR volume, whereas it was almost frequency-independent in the human brain. These findings should be helpful for extrapolating animal studies to humans.

Tissue models for RF exposure evaluation at frequencies above 6 GHz.

Exposures to radiofrequency (RF) energy above 6 GHz are characterized by shallow energy penetration, typically limited to the skin, but the subsequent increase in skin temperature is largely determined by heat transport in subcutaneous layers. A detailed analysis of the energy reflection, absorption, and power density distribution requires a knowledge of the properties of the skin layers and their variations. We consider an anatomically detailed model consisting of 3 or 4 layers (stratum corneum, viable epidermis plus dermis, subcutaneous fat, and muscle). The distribution of absorbed power in the different tissue layers is estimated based on electrical properties of the tissue layers inferred from measurements of reflected millimeter wavelength energy from skin, and literature data for the electrical properties of fat and muscle. In addition, the thermal response of the model is obtained using Pennes bioheat equation as well as a modified version incorporating blood flow rate-dependent thermal conductivity that provides a good fit to experimentally-found temperature elevations. A greatly simplified 3-layer model (Dermis, Fat, and Muscle) that assumes surface heating in only the skin layer clarifies the contribution of different tissue layers to the increase in surface skin temperature. The model shows that the increase in surface temperature is, under many circumstances, determined by the thermal resistance of subcutaneous tissues even though the RF energy may be deposited almost entirely in the skin layer. The limits of validity of the models and their relevance to setting safety standards are briefly discussed. Bioelectromagnetics. 39:173-189, 2018. © 2018 Wiley Periodicals, Inc.

Skin color and tissue thickness effects on transmittance, reflectance, and skin temperature when using 635 and 808 nm lasers in low intensity therapeutics.

OBJECTIVE: To examine the role of skin color and tissue thickness on transmittance, reflectance, and skin heating using red and infrared laser light. METHODS: Forty volunteers were measured for skin color and skin-fold thickness at a standardized site near the elbow. Transmittance, reflectance and skin temperature were recorded for energy doses of 2, 6, 9, and 12 Joules using 635 nm (36 mW) and 808 nm (40 mW) wavelength laser diodes with irradiances within American National Standards Institute safety guidelines (4.88 mm diameter, 0.192 W/cm2 and 4.88 mm diameter, 0.214 W/cm2 , respectively). RESULTS: The key factors affecting reflectance to an important degree were skin color and wavelength. However, the skin color effects were different for the two wavelengths: reflectance decreased for darker skin with a greater decrease for red light than near infrared light. Transmittance was greater using 808 nm compared with 635 nm. However, the effect was partly lost when the skin was dark rather than light, and was increasingly lost as tissue thickness increased. Dose had an increasing effect on temperature (0.7-1.6°C across the 6, 9, and 12 J doses); any effects of wavelength, skin color, and tissue thickness were insignificant compared to dose effects. Subjects themselves were not aware of the increased skin temperature. Transmittance and reflectance changes as a function of energy were very small and likely of no clinical significance. Absorption did not change with higher energy doses and increasing temperature. CONCLUSION: Skin color and skin thickness affect transmittance and reflectance of laser light and must be accounted for when selecting energy dose to ensure therapeutic effectiveness at the target tissue. Skin heating appears not to be a concern when using 635 and 808 nm lasers at energy doses of up to 12 J and irradiance within American National Standards Institute standards. Photobiomodulation therapy should never exceed the American National Standards Institute recommendation for the maximum permissible exposure to the skin. Lasers Surg. Med. 50:291-301, 2018. © 2017 Wiley Periodicals, Inc.

Maximum allowable exposure to different heat radiation levels in three types of heat protective clothing.

To determine safe working conditions in emergency situations at petro-chemical plants in the Netherlands a study was performed on three protective clothing combinations (operator's, firefighter's and aluminized). The clothing was evaluated at four different heat radiation levels (3.0, 4.6, 6.3 and 10.0 k∙W∙m-2) in standing and walking posture with a thermal manikin RadMan™. Time till pain threshold (43°C) is set as a cut-off criterion for regular activities. Operator's clothing did not fulfil requirements to serve as protective clothing for necessary activities at heat radiation levels above 1.5 k∙W∙m-2 as was stated earlier by Den Hartog and Heus1). With firefighter's clothing it was possible to work almost three min up to 4.6 k∙W∙m-2. At higher heat radiation levels firefighter's clothing gave insufficient protection and aluminized clothing should be used. Maximum working times in aluminized clothing at 6.3 k∙W∙m-2 was about five min. At levels of 10.0 k∙W∙m-2 (emergency conditions) emergency responders should move immediately to lower heat radiation levels.

Differential impact in young and older individuals of blue-enriched white light on circadian physiology and alertness during sustained wakefulness.

We tested the effect of different lights as a countermeasure against sleep-loss decrements in alertness, melatonin and cortisol profile, skin temperature and wrist motor activity in healthy young and older volunteers under extendend wakefulness. 26 young [mean (SE): 25.0 (0.6) y)] and 12 older participants [(mean (SE): 63.6 (1.3) y)] underwent 40-h of sustained wakefulness during 3 balanced crossover segments, once under dim light (DL: 8 lx), and once under either white light (WL: 250 lx, 2,800 K) or blue-enriched white light (BL: 250 lx, 9,000 K) exposure. Subjective sleepiness, melatonin and cortisol were assessed hourly. Skin temperature and wrist motor activity were continuously recorded. WL and BL induced an alerting response in both the older (p = 0.005) and the young participants (p = 0.021). The evening rise in melatonin was attentuated under both WL and BL only in the young. Cortisol levels were increased and activity levels decreased in the older compared to the young only under BL (p = 0.0003). Compared to the young, both proximal and distal skin temperatures were lower in older participants under all lighting conditions. Thus the color temperature of normal intensity lighting may have differential effects on circadian physiology in young and older individuals.

Finite element method simulating temperature distribution in skin induced by 980-nm pulsed laser based on pain stimulation.

For predicting the temperature distribution within skin tissue in 980-nm laser-evoked potentials (LEPs) experiments, a five-layer finite element model (FEM-5) was constructed based on Pennes bio-heat conduction equation and the Lambert-Beer law. The prediction results of the FEM-5 model were verified by ex vivo pig skin and in vivo rat experiments. Thirty ex vivo pig skin samples were used to verify the temperature distribution predicted by the model. The output energy of the laser was 1.8, 3, and 4.4 J. The laser spot radius was 1 mm. The experiment time was 30 s. The laser stimulated the surface of the ex vivo pig skin beginning at 10 s and lasted for 40 ms. A thermocouple thermometer was used to measure the temperature of the surface and internal layers of the ex vivo pig skin, and the sampling frequency was set to 60 Hz. For the in vivo experiments, nine adult male Wistar rats weighing 180 ± 10 g were used to verify the prediction results of the model by tail-flick latency. The output energy of the laser was 1.4 and 2.08 J. The pulsed width was 40 ms. The laser spot radius was 1 mm. The Pearson product-moment correlation and Kruskal-Wallis test were used to analyze the correlation and the difference of data. The results of all experiments showed that the measured and predicted data had no significant difference (P > 0.05) and good correlation (r > 0.9). The safe laser output energy range (1.8-3 J) was also predicted. Using the FEM-5 model prediction, the effective pain depth could be accurately controlled, and the nociceptors could be selectively activated. The FEM-5 model can be extended to guide experimental research and clinical applications for humans.