Diurnal changes in local skin water assessed via tissue dielectric constant 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.

Assessing Potential Circadian, Diurnal, and Ultradian Variations in Skin Biophysical Properties

A variety of skin measurements are routinely made in various clinical and research settings to evaluate the skin’s biophysical properties for diagnostic and research purposes. Such measurements include transepidermal water loss (TEWL), skin pH, sebum, skin blood flow (SBF), and tissue dielectric constant (TDC) as a measure of skin water. Given the various reported circadian, diurnal, and possible ultradian and other temporal variations in skin physiological processes, it is of value to have clarity as to possible temporal variations in skin’s biophysical properties associated with such processes. It was thus the purpose of this investigation to review and detail key elements of what is currently known regarding such variations and to provide a characterization that will permit informed judgments as to the sensitivity of the timing of measurements to optimize measurement reproducibility.

Understanding these variations and their possible oscillatory effects on skin biophysical properties may aid physicians in providing optimal treatment timing for dermatological conditions and offer researchers insight into optimal measurement timing. The major findings of the present investigation that systematically searched multiple databases and critically examined pertinent findings, revealed that of the several skin parameters reviewed, which included TEWL, pH, sebum, SBF, TDC, and thickness, each had at least one study describing a statistically significant within-a-day temporal change. The magnitude of these changes varied and may be large enough to be seriously considered when assessing these parameters in clinical and research settings. However, inconsistencies in reported temporal variations suggest that further systematic research is well warranted especially with respect to temporal within-a-day and day-to-day variabilities of TEWL, TDC, and mechanical properties. At present, the impact of this type of confounding variability on reported values for skin biophysical parameters is unclear and worthy of further clarification.

Spatial and Temporal Variability of Upper Extremity Edema Measures After Breast Cancer Surgery

Background: Tissue dielectric constant (TDC), as an index of local tissue water, and girth measurements are quantitative methods to measure and characterize lymphedema. Objective: To describe the spatial and temporal variability in arm girth and TDC values in women surgically treated for breast cancer and to describe the relationship between these measures. Methods and Results: This was a prospective longitudinal study that observed 36 women for 78 weeks after breast cancer surgery with lymph node removal. Arm circumferences and TDC values, as indices of local tissue water, were measured on both arms at multiple sites at postsurgery weeks 2, 4, 12, and 78 in women undergoing surgical breast cancer treatment with one or more axillary lymph nodes removed. TDC and girth values remained relatively uniform from visit-to-visit for both at-risk and contralateral control arms with no overall statistically significant difference in values (p > 0.05). There was a strong inverse correlation between arm girth and the TDC value in both the at-risk and control arms (p < 0.001). Overall, there was no statistically significant difference in TDC interarm ratios among visits or anatomical sites. TDC values for at-risk and control arms tended to significantly decrease with increasing distance from the wrist (p < 0.001). Conclusion: TDC arm values and girth measures remained relatively uniform in women after breast cancer surgery. The fact that TDC values are higher distally than proximally provides new information from which TDC measurements may be interpreted and also provides a better understanding of arm spatial variability in relation to girth measures.