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.