Effects of local forearm skin heating on skin properties

Skin Barrier Function Assessment: Electrical Impedance Spectroscopy Is Less Influenced by Daily Routine Activities Than Transepidermal Water Loss

BACKGROUND

Skin barrier function assessment is commonly done by measuring transepidermal water loss (TEWL). An important limitation of this method is the influence of intrinsic and extrinsic factors. Electrical impedance spectroscopy (EIS) is a lesser-established method for skin barrier function assessment. Some influential factors have been described, but no guidelines exist regarding the standardization of these measurements.

OBJECTIVE

To evaluate the effect size of daily routine activities on TEWL and EIS, as well as their correlation with age and anatomical differences.

METHODS

Healthy participants (n=31) were stratified into three age groups (18-29, 30-49, and ≥50 years). In a climate-controlled room, EIS and TEWL measurements were performed on the left and right volar forearm and abdomen.

RESULTS

Body cream application decreased TEWL and EIS values after 15 and 90 minutes. Skin washing decreased TEWL for 15 minutes and EIS values for at least 90 minutes. TEWL was increased 5 minutes after moderate to intense exercise. Coffee intake increased TEWL on the abdomen after 60 minutes. TEWL and EIS values did not correlate with participants' age and no anatomical differences were observed. No correlation was observed between TEWL and EIS.

CONCLUSION

Body cream application and skin washing should be avoided at least 90 minutes prior to measurements of TEWL and EIS. Exercise and coffee intake should also be avoided prior to TEWL measurements. EIS may be a promising tool for skin barrier function assessment as it is less affected by daily routine activities than TEWL.

Pressure Injury Mitigation in Prolonged Care: A Randomized Noninferiority and Superiority Trial

INTRODUCTION

Combat casualties are at increased risk for pressure injuries (PIs) during prolonged casualty care. There is limited research on operational PI risk mitigation strategies. The purpose of this study was to (1) compare a prototype mattress (AirSupport) designed for operational conditions versus the foldable Talon litter and Warrior Evacuation Litter Pad (WELP) on PI risk factors and (2) determine whether the Talon + AirSupport pad was noninferior and superior to the Talon + WELP on skin interface pressure.

MATERIALS AND METHODS

Healthy adults (N = 85; 20 men and 65 women), aged 18 to 55 years, were stratified based on body fat percentage and randomized into three groups: Talon (n = 15), Talon + AirSupport (n = 35), and Talon + WELP (n = 35). The participants were asked to lie in a supine position for 1 hour. The outcomes included skin interface pressure (body surface areas: Sacrum, buttocks, occiput, and heels), sacral and buttock skin temperature and moisture, and discomfort and pressure. The study was approved by the University of Washington Institutional Review Board.

RESULTS

Aim 1: The Talon had significantly higher peak skin interface pressure versus the AirSupport and WELP on the sacrum, buttocks, occiput, and heels. Skin temperature increase over the 1-hour loaded period was significantly lower on Talon versus AirSupport or WELP, reflecting a lower temperature-induced ischemic load. There was no significant difference in skin moisture changes or discomfort between the surfaces. Aim 2: The upper confidence limits for the difference in skin interface pressure (all body surface areas) for AirSupport versus WELP were below 25 mm Hg, establishing noninferiority of the AirSupport to the WELP. AirSupport was also superior to WELP for the peak interface pressure on the sacrum, occiput, and heels but not on the buttocks. Skin temperature changes (sacrum or buttocks) were not significantly different between the AirSupport and WELP.

CONCLUSIONS

The Talon litter presents a PI risk because of increased skin interface pressure, and hence, immediate action is warranted. The decreased PI risk associated with the lower skin interface pressures on the AirSupport and WELP was offset by the higher skin temperature, which may add the equivalent of 20 to 30 mm Hg pressure to the ischemic burden. Thus, any pressure redistribution intervention must be evaluated with a consideration for skin interface pressure, temperature, and moisture. Data from this study were applied to a predictive model for skin damage. Under operational conditions where resources and the environment may limit patient repositioning, it would be expected that casualties would suffer skin damage within 2 to 5 hours, with the occiput as the highest risk area. The severity of predicted skin damage is lowest on the AirSupport, which is consistent with the noninferiority and superiority of the AirSupport mattress compared to the WELP and Talon. Operational utility: The AirSupport and WELP, which were both superior to the Talon, are operationally feasible solutions to mitigate PI risk. The smaller size of the Talon (2.7 kgs compressible) versus the WELP (5 kgs noncompressible) may make them appropriate for different levels of the operational setting.

Impacts of Skin Eccrine Glands on the Measured Values of Transepidermal Water Loss

Transepidermal water loss (TEWL) is widely used to assess and quantify skin insensible water loss to assess skin's barrier function integrity. Low TEWL values are normally indicative of intact skin and a healthy functional barrier, whereas an increased TEWL reveals a disturbed or disrupted skin barrier. Because most skin sites at which these measurements are made have eccrine glands present, the contribution of the sweat gland activity to these measurements is variable and, in most cases, unknown. The separation between the contribution of water loss that is reflective of the skin barrier integrity versus that contributed via eccrine activation is not easy and is made more difficult since both components increase with increasing skin and environmental temperature. Endogenous factors that impact eccrine sweat gland activity include sympathetic nervous system activity, emotional stress, physical activity, eccrine gland density, and age. Exogenous factors that impact eccrine gland activity include ambient temperature and humidity and the climate where one resides. The aforementioned variables impact eccrine gland activity positively or negatively and therefore alter TEWL values accordingly. Although it may be theoretically possible to control all these factors, the difficulty in doing so results in only a few being controlled during most TEWL measurements. Such confounding processes may have impacted historical TEWL reference ranges and values previously reported. Thus, the impact of eccrine activation on standardly measured TEWL values is at this juncture unclear and may be a component contributing to some reported variability in TEWL values. To help clarify the issues, a literature review was conducted to investigate and summarize relevant prior research efforts and outcomes with respect to ways to consider eccrine activity in TEWL measurements and estimate the contribution of eccrine gland activity to TEWL values. Online databases such as Excerpta Medica Database (EMBASE), Public/Publisher Medline (PubMed), Elton B. Stephans Company (EBSCO), Google Scholar, and Wiley Online Library were searched with "transepidermal water loss" or "TEWL" in the title combined with "eccrine glands" or "sweat" anywhere in the text. The present findings indicate a multiplicity of biological and environmental variables impacting eccrine gland activity and thereby potentially affecting measured TEWL values. Even if laboratory conditions adhere to various guidelines and recommendations, it is not yet possible to separate the eccrine activation component from the parameter of true interest in the assessment of the skin's physiological barrier function except for full gland deactivation. The amount that such eccrine gland activation impacts the measured value of TEWL is generally not determined using currently available methods and the only sure way to eliminate a confounding effect is to inactivate the glands during such TEWL measurements. Because such eccrine gland deactivating approach is not usually desirable or even possible, other approaches would be recommended. One would be the development of a measuring device that could distinguish between the component of TEWL that is associated with the skin barrier function and the other that is attributable to sweat gland activation. Further research and development along these lines appear warranted.

Human exposure to radiofrequency energy above 6 GHz: review of computational dosimetry studies

International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity 'absorbed/epithelial power density' has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 s). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.