Skin Tissue Water Variations in Different Races Measured via the 300 MHz Tissue Dielectric Constant Method

Objective. To determine if skin tissue water, based on tissue dielectric constants (TDC), are different among anatomical sites and races and if TDC-values correlate with total body water percentage (TBW%). Background. Measuring TDC via the open-ended coaxial probe 300Mz method is a useful non-invasive measure for edema assessment but site, race and TBW% effects on TDC are unknown. Such information would aid in TDC clinical usage. Methods. TDC was measured in triplicate to depths of 1.5 and 5.0 mm bilaterally at the first intercostal space mid-clavicle (chest) and anterior forearm (arm) and to 1.5 mm at the medial malleolus (ankle). TBW was measured standing and supine with two different devices according to whole body impedance measurements. To date, measurements were done in five races: White (16), Black (4), Hispanic (5), Asian (7) and Asian Indian (10) for a total N = 42 (23 male). The study design calls for N = 100 with 20 per race. Results. Because the current N is insufficient for race comparisons, results focus on site variations in TDC and relationships between TDC and TBW. Composite TDC values for chest, arm and ankle (n = 84) were 36.0±5.3, 34.5±3.1 and 28.2±6.4 (p < 0.001) for 1.5mm-depth and for chest and arms at 5.0 mm-depth were 30.2±4.7 vs. 30.0±6.3 (p = 0.751). The 5.0 mm-depth values were significantly less (p < 0.001) than corresponding 1.5 mm-depth values. Standing and supine TBW% were 57.7±6.9% vs. 56.3±5.79%. TBW% correlated best with TDC-5.0mm measured on the arm (r = 0.635, p < 0.001). Conclusions. There are significant anatomical site and depth variations in TDC that may correlate with TBW%.