BIOELECTRICAL-IMPEDANCE ANALYSIS IN HUMAN IMMUNODEFICIENCY VIRUS-INFECTED PATIENTS - COMPARISON OF SINGLE-FREQUENCY WITH MULTIFREQUENCY, SPECTROSCOPY, AND OTHER NOVEL APPROACHES

Bioelectrical impedance (BIA), a prediction method for estimating body water compartments and body cell mass (BCM), is being increasingly us ed in studies of human immunodeficiency virus (HIV)-related wasting, b ut there are few validation studies of the method in this group. The a im of this study is to examine the relationship between impedance meas urements and body water compartments in patients with advanced HN dise ase, and to investigate whether the newer approaches of multifrequency BIA, BIA spectroscopy, logarithmic transformation using a parallel ci rcuit model, and direct calculation from electrical theory offer any a dvantage over traditional single-frequency BIA. We measured total body water (TBW) by deuterium dilution and extracellular water by bromide dilution in 33 patients with advanced HIV disease. Intracellular water and BCM were calculated from these results. Impedance was measured ov er a range of frequencies using a multifrequency analyzer. The relatio nship between impedance index at various frequencies and body water co mpartments was assessed by correlation and linear regression. We found that impedance index at higher frequencies had a closer relationship to TBW (r = 0.86, standard error of the estimate [SEE] = 2.96 at 1000 kHz) and at lower frequencies a closer relationship to extracellular w ater (ECW) (r = 0.47, SEE = 3.13 at 0 kHz) than the traditional 50 kHz measurement (r = 0.84, SE = 3.11 for TBW; r = 0.44, SEE = 3.19 for EC W), but the differences were marginal and not statistically significan t. None of the other novel approaches tested were significantly better than traditional single frequency measurement. The 50 kHz equation fo r BCM developed in this study [BCM (kg) = (0.360331 x Ht(2)/Z(50)) + ( 0.151123 x Wt) - 2.95] may be useful to investigators using BIA for HI V-wasting studies. Nutrition 1998; 14:658-666. (C) Elsevier Science In c. 1998.