Assessing Lower Extremity Lymphedema Using Upper and Lower Extremity Tissue Dielectric Constant Ratios: Method and Normal Reference Values

Harvey N. Mayrovitz, PhD. Lymphatic Research Biology, February, 2019

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Assessing Lower Extremity Lymphedema Using Upper and Lower Extremity Tissue Dielectric Constant Ratios: Method and Normal Reference Values

Harvey N. Mayrovitz, PhD. Lymphatic Research Biology, February 2019

Background: Lower extremity swelling accompanies many conditions, including gynaecological surgery and chronic venous dysfunction. Some clinical and quantitative assessment methods exist, but other ways to rapidly assess early lymphedema and track changes are needed. Our goal was to use lower to upper extremity intraside tissue dielectric constant (TDC) ratios with the specific aim of providing normal reference values potentially useful as a comparison measure against which persons at risk for lower extremity lymphedema might be evaluated.

Methods and Results: TDC ratios (calf/forearm, foot/forearm) were measured in 44 young (25.1–2.2 years) and 60 mature (60.1–11.5 years) volunteers equally divided by gender. Foot/forearm and calf/forearm ratios did not differ between genders. For mature, values measured on dominant sides were 1.050–0.151 and 1.013–0.162, respectively. Lymphedema threshold ratios, calculated as the mean ratio plus twice their respective standard deviations, were for calf/forearm and foot/forearm 1.352 and 1.337, respectively. As an initial test of the thresholds, they were compared to TDC ratios determined in six patients with lower extremity oedema due to congestive heart failure.

Conclusion: Based on these findings, it is proposed that a calf/forearm TDC ratio that exceeds 1.35 is suggestive of lower extremity lymphedema and that the calf/forearm ratio could be used to track temporal changes and therapy-related improvements. The test of these conclusions requires future research in which these intraside TDC ratios and thresholds are evaluated in patients with lower extremity lymphedema and venous-related oedema. This work provides the reference values for such comparisons to be systematically done.

Main findings

  • The measurement method utilizes ratios of the lower extremity to upper extremity TDC values to minimize the effect of variation in absolute TDC values among individuals and to determine the resultant reference thresholds. More specifically, they sought to provide initial intraside lower to upper extremity TDC ratio reference values as a guide to subsequent assessments of patients in a clinical setting, using a protocol that would be time practical in a busy practice.
  • There were two phases. the first of which utilized a group of young adults in whom extensive bilateral TDC measurements could be made at multiple upper and lower extremity sites. The specific aims of phase 1 were to determine the extent to which intraside lower to upper extremity TDC ratios differ dependent on (1) skin depth to which TDC measurements were made, (2) anatomical sites used, and (3) intraside used being dominant or nondominant. The second phase consisted of more limited measurements in a group of mature adults with only one body side used with measurements in fewer selected anatomical sites. The specific aim was to provide the needed initial reference ratios in an age group more likely to be representative of the subsequent clinical population.
  • The participants were measured in supine.
  • The number of measurement sites and depths used in MATURE was purposefully made less than for YOUNG so that the MATURE measurement set could better simulate a pattern that might actually be used in a busy clinical setting with time constraints.
  • For YOUNG, there were three lower extremity measurement sites (foot dorsum, medial calf, and lateral calf);
  • For MATURE, there were two (foot dorsum and medial calf). The foot dorsum site was between first and second toes just proximal to their union. The calf sites were 8cm proximal to the centre of the corresponding malleolus.
  • For YOUNG, measurements were bilateral; for MATURE, measurements were unilateral on the dominant side. For both groups, the upper extremity measurement site was the anterior forearm 5cm distal to the antecubital fossa.
  • In YOUNG, an additional site was the hand palm in the centre of the thenar eminence.
  • TDC measurements on lower extremity sites were started after completing upper extremity TDC measurements.
  • In MATURE, absolute TDC values of males exceeded those of females at each measured site by amounts ranging from 13.3% at the foot, 15.6% at the forearm, and 21.7% at the medial leg. In YOUNG, absolute TDC values of males exceeded those of females at foot and forearm by 17% and 21.2%, respectively. Despite these absolute value differences, the intraside ratios did not significantly differ between genders for either MATURE or YOUNG.
  • Based on these findings, they proposed that a leg/ arm TDC ratio that exceeds 1.35 is suggestive of the presence of lower extremity lymphedema.
  • They would also propose that a reduction in this ratio could be used to track therapy-related improvements.