Young adult gender differences in forearm skin-to-fat tissue dielectric constant values measured at 300 MHz

Intra-day variations in volar forearm skin hydration

BACKGROUND

Skin hydration (SKH) measurements are used for multiple purposes: to study skin physiology, to clinically investigate dermatological issues, and to assess localized skin water in pathologies like diabetes and lymphedema. Often the volar forearm is measured at various times of day (TOD). This report aims to characterize intra-day variations in volar forearm SKH to provide guidance on expected TOD dependence.

MATERIALS AND METHODS

Forty medical students (20 male) self-measured tissue dielectric constant (TDC) on their non-dominant forearm in triplicate as an index of local skin tissue water every 2 h starting at 0800 and ending at 2400 h. All were trained and pre-certified in the procedure and had whole-body fat (FAT%) and water (H2O%) measured. Day average TDC (TDCAVG) was determined as the average of all time points expressed as mean ± SD.

RESULTS

Males versus females had similar ages (25.1 ± 2.2 years vs. 25.1 ± 1.5 years), higher H2O% (56.6 ± 5.0 vs. 51.8 ± 5.7, p = 0.002), and higher TDCAVG (32.7 ± 4.1 vs. 28.5 ± 5.1, p = 0.008). TDC values were not significantly impacted by H2O% or FAT%. Female TDC exhibited a significant decreasing trend from morning to night (p = 0.004); male TDC showed no trend.

CONCLUSION

Skin water assessed by TDC shows some intra-day variations for females and males but with quite different temporal patterns. Clinical relevance relates to the confidence level associated with skin hydration estimates when measured at different times of day during normal clinic hours which, based on the present data, is expected to be around 5% for both males and females.

Breast Cancer-Related Lymphedema Assessed via Tissue Dielectric Constant Measurements

This review describes the use of tissue dielectric constant (TDC) measurements mainly in the assessment of breast cancer-related lymphedema (BCRL). PubMed, Web of Science, and EMBASE databases were initially searched using criteria that included the terms "dielectric" and "lymphedema." The initial search yielded a total of 131 titles. After removing studies not focused on upper extremity lymphedema, 56 articles remained. These articles, together with relevant articles from their bibliographies, formed the basis of the review. The findings show the potential utility and applications of TDC measurements to help detect and track BCRL, whether present in limbs, breasts, or trunks. It is reported as a non-invasive, simple-to-use method, with each measurement requiring less than 10 seconds, suggesting its practicality and useability as an in-office or in-clinic screening and tracking method. Although there are various ways to quantitatively evaluate lymphedema, most, if not all, are restricted to measurements on limbs. Thus, one significant advantage of the TDC approach is that almost any local region of interest can be effectively measured and tracked, which, for BCRL, could include specific regions of arms or hands, breasts, and truncal areas.

Medical Applications of Skin Tissue Dielectric Constant Measurements

Tissue dielectric constant (TDC) values assess certain skin properties that are dependent on multiple factors but mainly on the relative amount of water content within a locally measured tissue volume. Because of the non-invasive nature of these measurements and their ease of use, the method has been widely used in various medically related applications. The goal of this paper was to review and describe the uses and findings of such TDC measurements, considering and including the wide array of medical applications. The review is in part based on information derived from an analysis of published material obtained via literature searches of four major electronic databases and, in part, based on the author's experience with the TDC measurement methods and their various applications and his professional experiences. The databases searched were PubMed, Web of Science, EMBASE, and CINAHL Complete. Based on the initial search criteria, a total of 1257 titles were identified. After removing duplicates and filtering according to relevancy, 160 remained for detailed further review. In some cases, the bibliography of these retrieved articles provided additional sources. The findings demonstrate multiple research and medical uses and applications of TDC measurements, focusing on detecting and quantifying localized edema and lymphedema in multiple target sites. These include the upper and lower extremities, breasts, and trunk as regions involved in medical conditions causing lymphedema. In addition, the findings suggest that TDC evaluations are a convenient, non-invasive method to study and evaluate other conditions impacting skin, including diabetes mellitus and skin wounds or ulcers. Its ability to detect aspects of tissue changes simply and rapidly at almost any anatomical location makes it a useful tool for investigating multiple dermatological conditions and their treatment as future applications of this method.

Variation in Leg Tissue Dielectric Constant Values of Healthy Young Adult Females With and Without Compression Bandaging

Background The clinical efficacy of a compression application has been often limited to the assessment of the change in limb volume, change in clinical symptoms (i.e., wound size, pain, range of motion, incidence of cellulitis), or vascular hemodynamics of the whole limb. Assessing compression-related biophysical changes of a localized area, such as around a wound, or in an area outside of an extremity cannot be objectively assessed by these measurements. Tissue dielectric constant (TDC) values, which provide a measure of the local tissue water (LTW) content, offer an alternative method to document variation in the LTW content of the skin in a specific location. The goals of the present research were (1) to characterize TDC values, expressed as percentage tissue water, from multiple areas along the medial aspect of the lower leg of healthy volunteers and (2) to explore the potential utilization of the TDC values to assess change in tissue water content in a localized area following compression applications. Methods TDC was measured at 10, 20, 30, and 40 cm proximal to the medial malleolus on the medial aspect of the right leg of 18 young adult healthy women with an age range of 18-23 years and a body mass index of 18.7 to 30.7kg/m^2.. TDC was measured at baseline and after 10 minutes of exercise with compression in place on three separate days during which three different compression applications were assessed: a longitudinal elastic stockinette, a two-layer cohesive compression kit, and a combination of the two. Leg circumferences and compression-related interface pressures were also measured. Results Test-Retest Reliability of circumferential measurements and TDC values evaluated using Intraclass correlation coefficient (ICC _3,1) revealed excellent and moderate-to-good reliability, respectively. Analysis of TDC values along the length of the limb using Friedman's test, revealed a small but statistically significant overall difference among baseline TDC values attributable to a smaller value at 40 cm. The largest difference in cumulative average was 7.7% which occurred between 20 and 40 cm, with all other differences between locations less than 1%. No significant differences between the compression applications were observed. Conclusion  The present findings demonstrate the utility of TDC measurements as a modality to assess compression-related changes in the legs of healthy women as a foundation for their potential use in assessing outcomes of compression treatments for persons with lower extremity edema or lymphedema. The absence of a significant change in TDC values in these healthy non-edematous conditions and the demonstrated reliability of the TDC measurements on three different days provides further support for the utility of such applications of TDC measurements. The extension to patients with lower extremity edema or lymphedema needs to be evaluated.

Physiological, Pathological, and Circadian Factors Impacting Skin Hydration

Thismanuscript focuses on the physiological, environmental, nutritional, circadian, and aging factors affecting skin tissue water and hydration parameters. The literature findings indicate a multiplicity of interacting processes among these parameters, ultimately impacting skin hydration in normal skin and playing a role in conditions such as atopic dermatitis and psoriasis. The maintenance of adequate skin hydration, aided by the proper functioning of the skin’s protective barrier, is facilitated by stratum corneum integrity with the presence of tight junctions and lipids such as ceramides, each of which is impacted by changes in most of the evaluated parameters. Abnormalities in aquaporin 3 (AQP3) expression and associated deficits in skin hydration appear to have a role in atopic dermatitis and psoriasis. AQP3 hydration-related aspects are influenced by circadian rhythms via modulations associated with CLOCK genes that alter AQP3 protein expression. Ultraviolet exposure, aging, and low temperatures are among those factors that affect skin ceramide composition, potentially leading to increased transepidermal water loss and negatively impacting skin hydration. Vitamin C, collagen, and probiotics may increase ceramide production and improve skin hydration. The extent to which each of the different evaluated factors affects skin hydration varies but is usually large enough to consider their potential effects when investigating skin in research and clinical settings.

Circumferential and Depth Variations in Tissue Dielectric Constant Values as Indices of Lower Leg Localized Skin Water

The primary goal of this study was to quantify circumferential (medial, anterior, lateral) and measurement depth variations (0.5 mm, 1.5 mm, 2.5 mm) in tissue dielectric constant (TDC) values as an aid to their use to assess the presence and progression of lower extremity edema and lymphedema. Measurements were done in 30 healthy non-edematous women to provide reference data to estimate expected values and thresholds when evaluating clinical edematous or lymphedematous conditions. A second goal was to determine the extent to which TDC values evaluated at lower leg sites depend on body mass index (BMI). The study protocol (#12180901) was approved by the university’s institutional review board and subjects were evaluated after signing an approved informed consent. The study group had an age range of 19-54 years with a mean age and SD of 30.6 ± 10.1 years and had a BMI between 18.1-44.1 Kg/m² with a mean BMI and SD of 24.5 ± 5.4 Kg/m². The main findings show that at the three circumferential sites (medial, anterior, and lateral) located eight cm from the mid-malleolus, there are small but statistically significant differences in TDC values at every measurement depth (0.5 mm, 1.5 mm and 2.5 mm). For each depth, the maximum difference occurs between the medial and lateral locations with lateral locations having a greater TDC value at all depths. Despite the wide range of BMI values of the subjects evaluated, no significant relationship between TDC value and BMI was detected. It is concluded that TDC measurements in the lower leg reveal statistically significant differences among circumferential sites and measurement depths that should be considered when evaluating or tracking lower extremity tissue water changes associated with edema, lymphedema or other conditions related to skin water. The absolute values of these non-edematous TDC values herein determined may provide a basis for calculating TDC thresholds applicable to edematous or lymphedematous lower leg conditions.

Measurement and image-based estimation of dielectric properties of biological tissues —past, present, and future—

The dielectric properties of biological tissues are fundamental pararmeters that are essential for electromagnetic modeling of the human body. The primary database of dielectric properties compiled in 1996 on the basis of dielectric measurements at frequencies from 10 Hz to 20 GHz has attracted considerable attention in the research field of human protection from non-ionizing radiation. This review summarizes findings on the dielectric properties of biological tissues at frequencies up to 1 THz since the database was developed. Although the 1996 database covered general (normal) tissues, this review also covers malignant tissues that are of interest in the research field of medical applications. An intercomparison of dielectric properties based on reported data is presented for several tissue types. Dielectric properties derived from image-based estimation techniques developed as a result of recent advances in dielectric measurement are also included. Finally, research essential for future advances in human body modeling is discussed.

Noninvasive Measurements of Breast Cancer-Related Lymphedema

Breast cancer-related lymphedema (BCRL) presents as swelling in the arm, hand, trunk, or breast at varying times after completion of breast cancer treatment. Its reported incidence varies widely in part due to its dependence on the type and extent of the treatment, co-present pre-treatment risk factors, and the criteria used to define its presence. Central to this issue is the quantitative measures that are variously used to specify lymphedema thresholds for its detection and tracking over time and during treatment. The goal of this paper is to discuss these issues and the methods available for the non-invasive quantitative assessment of BCRL. Operational principles and advantages and limitations of the various methods and their clinical history of use and effectiveness are discussed. 

Subepidermal Moisture and Pressure Injury in a Pediatric Population: A Prospective Observational Study

PURPOSE

To describe relationships between subepidermal moisture (SEM) and visual skin assessment of pressure injury (PI) in children.

DESIGN

Prospective descriptive study.

SUBJECTS AND SETTING

Twenty-four participants aged 8 to 16 years recruited from a pediatric orthopedic unit in a children's hospital in Ireland.

METHODS

Subepidermal moisture measured with the SEM scanner (Bruin Biometrics, Los Angeles, California) ranged from 0 to 7 picoFarads [pF], and visual observation of trunk and heels occurred daily for 3 days after admission to the unit and/or after surgery. Skin was assessed for discoloration categorized as blanchable erythema, stage 1 PI, or deep tissue injury (DTI). Any open wound PI was classified as stage 2, 3, 4, or unstageable. Demographic, medical, and pain data were collected. Chi-square test, t tests, analysis of variance, and regression were used to describe data and examine relationships.

RESULTS

Participants were pediatric patients; 100% (n = 24) were white, 62% (n = 15) were female, 8 to 16 years of age (mean = 12.5 ± 2.5 years), and 29% (n = 7) had fractures and 71% (n = 17) surgery diagnoses. Blanchable erythema incidence was 21% (n = 5) and stage 1 PI incidence was 42% (n = 10); nearly all at heels. Deep tissue injury incidence was 4% (one sacral DTI). Stage 2 or greater PI incidence was 4% (one heel stage 2 PI). For skin that was assessed as normal in this pediatric population, SEM for trunk was 2.65 to 2.76 pF and for heels 2.37 to 2.41 pF. Subepidermal moisture for blanchable erythema and stage 1 PI was higher (range, 3.2-3.7 pF) and significant at trochanters and heels (left trochanter: P = .003; right trochanter: P = .02; right and left heels: P = .000). Nominal regression, controlling for participant and assessment day, showed SEM a predictor of erythema and stage 1 PI at heels. We also found that SEM was higher with pain (significant at sacrum and heels).

CONCLUSIONS

In this pediatric population, SEM values over skin assessed as normal are lower than SEM values reported for normal skin in adults, 2.37 to 2.76 pF. Subepidermal moisture was significantly higher for blanchable erythema and stage 1 PI at trochanters and heels, and with the presence of pain at sacrum and heels. We recommend that SEM should be examined for detecting PIs in pediatric populations; SEM and pain should be explored in larger pediatric and adult populations.

An Approach Toward Assessing Head-and-Neck Lymphedema Using Tissue Dielectric Constant Ratios: Method and Normal Reference Values

Background: There are multiple methods to quantitatively assess limb lymphedema, but quantitative methods to assess external lymphedema in persons with head-and-neck lymphedema are quite limited. Quantification in this difficult condition currently uses multiple time-consuming head, face, and neck metric measurements, the accuracy of which is unclear. Thus, there is an important need for a new approach that is sufficiently convenient yet accurate to quantify head-and-neck lymphedema. The approach adopted was to use tissue dielectric constant (TDC) measurements that depend on tissue water, at neck and a submental area, and normalize these to TDC values at the forearm as a way to develop subject-independent indices. Methods and Results: TDC was measured in 60 self-reported healthy nonlymphedematous adults (34 female, 18-81 years, 18.5-45.7 Kg/m²) at two neck sites and one arm site bilaterally and at a submental area. Neck-to-arm-index (NAI) and submental-to-arm-index (SAI) ratios were calculated. TDC values (mean ± standard deviation [SD]) for neck, submental, and arm were, respectively, 37.4 ± 6.9, 35.9 ± 7.7, and 30.1 ± 4.6. Mean NAI and SAI values were 1.253 ± 0.222 and 1.214 ± 0.296 respectively. Head-and-neck lymphedema thresholds calculated as mean + 2.5 SD were for NAI and SAI 1.80 and 1.95, respectively. Conclusions: An approach to help quantify and track head-and-neck lymphedema using TDC neck and/or submental values normalized to a person's forearm TDC values indicates threshold values between 1.80 and 1.95. These ratios, denoted as NAI and SAI, are suggested for use to detect and track changes in lymphedema status based on a patient's changing indices associated with lymphedema treatment.

Tissue Dielectric Constant Measures in Women With and Without Clinical Trunk Lymphedema Following Breast Cancer Surgery: A 78-Week Longitudinal Study

OBJECTIVE

Following breast cancer surgery with lymph node removal, women are at risk of developing lymphedema in the upper extremity or trunk. Currently, trunk lymphedema diagnosis relies on a clinical assessment because no quantifiable standard method exists. Tissue dielectric constant (TDC) values are quantifiable measures of localized skin tissue water and may be able to detect trunk lymphedema. The goal of this study was to (1) compare parameters derived from TDC measurements with those derived from clinically accepted criteria for trunk lymphedema in women following breast cancer surgery and (2) explore the potential utility of TDC to detect trunk lymphedema early in its progression.

METHODS

This prospective longitudinal study, a secondary analysis from a larger study, observed women with and without clinically determined truncal lymphedema following breast cancer surgery. TDC was measured on the lateral trunk wall at post-surgery weeks 2, 4, 12, and 78 in women who had surgical breast cancer treatment with lymph node removal. Clinical assessment for trunk lymphedema was determined at 78 weeks by a lymphedema expert. Comparison of TDC measurements in women with and without clinical trunk lymphedema was analyzed.

RESULTS

Clinical assessment identified trunk lymphedema in 15 out of 32 women at 78 weeks. These women had TDC ratios statistically higher than women without truncal lymphedema.

CONCLUSION

The overall findings indicate that TDC has the ability to quantify trunk lymphedema and might be valuable in early detection.

IMPACT

TDC may be a beneficial tool in the early detection of breast cancer-related trunk lymphedema, which could trigger intervention.

LAY SUMMARY

A new device may help recognize trunk lymphedema in patients with breast cancer so they could receive appropriate treatment.

Heat-related changes in skin tissue dielectric constant (TDC)

The impact of 20 min of whole-body heating (WBH) on the tissue dielectric constant (TDC) of forearm and hand skin was evaluated in 24 young adults. TDC was measured in triplicate at 300 MHz using an open-ended transmission line method in which the effective measurement depth was about 2 mm. TDC measurements are an effective way to assess and track localized oedema and lymphoedema. The underlying hypothesis was that heat-induced eccrine gland activation would increase TDC values via an increase in fluid within the TDC measurement volume. The goal was to test this concept and to determine the magnitude of the change when environmental temperatures were elevated to near 42°C and to estimate TDC recovery time. The practical aspect of this research is motivated by the fact that patients in whom such measurements are made may arrive at the clinic in various states of sweat gland activation. Thus, knowledge of the effect of such activation on measured TDC values permits better understanding of possible relationships between such activation and TDC values. Results showed that increasing environmental temperature from 23·3 ± 1·6 to 41·5 ± 1·3°C increased forearm and thenar eminence skin temperatures to 37·8 ± 0·5 and 37·9 ± 0·4°C, respectively. These changes were associated with increases in TDC at arm from 30·7 ± 4·6 to 36·3 ± 5·7 (18·2%) and at hand from 34·7 ± 4·9 to 45·1 ± 5·5 (30%). Based on calculated TDC recovery rates, it is concluded that temperature-related TDC variability can be minimized using a wait time of at least 15 min after bandage removal prior to TDC measurements in affected limbs.

Possible applications of normative lower to upper limb ratios of tissue dielectric constant to lower extremity edema

BACKGROUND

Lower extremity edema occurs in many conditions including congestive heart failure, lymphedema, diabetes-related, kidney and liver disease, chronic venous insufficiency with venous hypertension. Clinical edema assessment methods are often subjective and variable. Our goals were to introduce a simple noninvasive measurement procedure potentially useful to characterize lower extremity edema by providing normative values from which edema thresholds might emerge.

METHODS

Tissue dielectric constant (TDC) values, as indices of skin-to-fat tissue water, were measured on foot dorsum, lower medial leg and anterior forearm of 88 adults (44 female) with ages ranging from 19-77 years with BMI ranging from 18.3-40.6 kg/m2. From these direct measurements lower-to-upper extremity TDC ratios (foot/arm and leg/arm) were determined for each gender. Possible edema threshold ratios were calculated as the mean lower-to-upper ratio to which was added two standard deviations of the overall ratio thereby providing initial thresholds for future testing.

RESULTS

Results showed that at each anatomical site absolute TDC values for males significantly exceed those of females (P<0.001). Male vs. female TDC values were 33.0±5.4 vs. 27.7±4.0 for the forearm, 34.8±6.5 vs. 27.5±4.6 for the leg, and 32.5±6.5 vs. 28.7±5.1 for the foot. In contrast, the foot/arm and leg/arm ratios were similar between genders ranging 0.990±0.144 to 1.063±0.170. Corresponding lower extremity to upper extremity threshold ratios ranged from 1.278 for foot/arm to 1.403 for leg/arm. The composite ratios considering both gender ration (N.=88) yielded a composite threshold foot/arm ratio of 1.387 and a leg/arm threshold ratio of 1.324.

CONCLUSIONS

This assessment method together with the normative ratios and calculated thresholds may aid in rapid detection of lower extremity edema in patients and possibly as a way to quantitatively track changes in edema status with time or treatment. However, the suitability of these thresholds is subject to future validation in persons with clearly defined lower extremity edema for which this report's findings serve as an initial quantitative starting point.

Minimum Detectable Changes Associated with Tissue Dielectric Constant Measurements as Applicable to Assessing Lymphedema Status

Background: Tissue dielectric constant (TDC) measurements are increasingly being used as a tool to help characterize lymphedema features, detect its presence, and assess treatment related changes. Although the underlying physics of this technology has been well described in the literature, there has been little systematic study of in vivo reliability aspects. A central unanswered question is the minimal detectable change (MDC) that, with a given level of confidence, may be ascribed to this technology. Our goal was to address this issue using test-retest measurements from which intraclass correlations coefficients (ICC) and MDC could be estimated. Methods and Results: Forty volunteers (20 females) aged 19-61 years with body mass indices of 14.7-47 kg/m² and body fat percentages of 12.0%-48.9% were evaluated. Two measurers (M1 and M2) used two different TDC measuring devices (multiprobe and compact) to measure TDC in triplicate sequentially and bilaterally at three locations; anterior forearm, hand palmar mid-thenar eminence, and dorsum mid-web. These measurements were made by each measurer twice constituting test-retest values (T1 and T2). From these measurements ICC_2,1 and MDC at 95% confidence were determined for each site and probe for absolute TDC values and for inter-side ratios. MDC values for absolute TDC ranged from 2 to 9 TDC units, and for inter-side ratios ranged from 5.3% to 8.0% depending on site and probe. ICC_2,1 values ranged from 0.765 to 0.982. Conclusions: The MDC values herein documented may be used to provide guidance to aid interpretation of measured TDC changes or differences in a clinical environment.

Sensor-Based Detection of the Severity of Hyperkeratosis in the Teats of Dairy Cows

The aim of this study was to evaluate whether the severity of hyperkeratosis (HK) in the teats of dairy cows can be assessed by a dielectric measurement. The study focused on surveying the occurrence of hyperkeratosis in a total of 241 teats of lactating dairy cows. A scoring system consisting of four categories was used to macroscopically assess the severity of HK. Additionally, the dielectric constant (DC) of all teats with milkability was measured in a double iteration with the MoistureMeterD (Delfin Technologies, Kuopio, Finland) on four different days. The Spearman rank correlation coefficient revealed a negative correlation between the DC and HK score (rs = −0.55 to −0.36). The results of the regression analysis showed that the DC values differed significantly between healthy teat ends (≤2) and teat ends with HK (≥3). Thus, the non-invasive measurement of DC provides a promising method of objectively assessing the occurrence and severity of HK.

The revised EEMCO guidance for the in vivo measurement of water in the skin

BACKGROUND

Noninvasive quantification of stratum corneum water content is widely used in skin research and topical product development.

METHODS

The original EEMCO guidelines on measurements of skin hydration by electrical methods and transepidermal water loss (TEWL) by evaporimeter published in 1997 and 2001 have been revisited and updated with the incorporation of recently available technologies.

RESULTS

Electrical methods and open-chamber evaporimeters for measurement of TEWL are still the preferred techniques to measure the water balance in the stratum corneum. The background technology and biophysics of these instruments remain relevant and valid. However, new methods that can image surface hydration and measure depth profiles of dermal water content now available. Open-chamber measurement of TEWL has been supplemented with semiopen and closed chamber probes, which are more robust to environmental influence and therefore convenient to use and more applicable to field studies. However, closed chamber methods interfere with the evaporation of water, and the methods cannot be used for continuous monitoring. Validation of methods with respect to intra- and inter-instrument variation remains challenging. No validation standard or test phantom is available.

RESULTS AND CONCLUSIONS

The established methods for measurement of epidermal water content and TEWL have been supplemented with important new technologies including methods that allow imaging of epidermal water distribution and water depth profiles. A much more complete and sophisticated characterization of the various aspects of the dermal water barrier has been accomplished by means of today's noninvasive techniques; however, instrument standardization and validation remain a challenge.

Note: Hybrid-π model and parameter extraction method for electrode-electrolyte interface characterization with superbly accurate reactance

This paper presents an equivalent circuit model for the electrode-electrolyte interface and aims at improving the modeling accuracy of the parasitic effects at frequencies up to 300 MHz. Different from the conventional model, the electrode inductances, body loss capacitances, and body loss resistances are all included in the proposed hybrid-π model. In addition, the S-parameters obtained by a vector network analyzer are innovatively used to extract the parameters of the electrode-electrolyte interface model for a frequency range from 10 Hz to 300 MHz. Since reactance is proportional to frequency, the proposed technique can precisely calculate the parasitic effects at higher frequencies. Verified by experiments, the hybrid-π model presents better accuracies when fitted to both the phases and magnitudes of S11 and S21. The superb modeling accuracy of this work is beneficial for biomedical applications that have an electrode-electrolyte interface.