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

Lower extremity swelling accompanies many conditions, including gynecological 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. 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 edema due to congestive heart failure. 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 edema. This work provides the reference values for such comparisons to be systematically done.