Reliability of multiple frequency bioelectrical impedance analysis: An intermachine comparison

Abstract

The technical reliability (i.e., interinstrument and interoperator reliability) of three SEAC‐swept frequency bioimpedance monitors was assessed for both errors of measurement and associated analyses. In addition, intraoperator and intrainstrument variability was evaluated for repeat measures over a 4‐hour period. The measured impedance values from a range of resistance‐capacitance circuits were accurate to within 3% of theoretical values over a range of 50–800 ohms. Similarly, phase was measured over the range 1°–19° with a maximum deviation of 1.3° from the theoretical value. The extrapolated impedance at zero frequency was equally well determined (±3%). However, the accuracy of the extrapolated value at infinite frequency was decreased, particularly at impedances below 50 ohms (approaching the lower limit of the measurement range of the instrument). The interinstrument/operator variation for whole body measurements were recorded on human volunteers with biases of less than ±1% for measured impedance values and less than 3% for phase. The variation in the extrapolated values of impedance at zero and infinite frequencies included variations due to operator choice of the analysis parameters but was still less than ±0.5%. Am. J. Hum. Biol. 9:63–72 © 1997 Wiley‐Liss, Inc.

Predicting composition of leg sections with anthropometry and bioelectrical impedance analysis, using magnetic resonance imaging as reference

“…If circularity was assumed then total cross-sectional area calculated from circumference (thigh slice A, 162 cm# ; slice B, 238 cm# ; slice C, 312 cm# : calf slice A, 128 cm# ; slice B, 119 cm# ; slice C, 89 cm#) would be overestimated in all cases compared with summed MRI estimates of component tissues (Table 1). impedance at 50 kHz for the 20-cm thigh section was 22.8 (5.3) Ω and that for the 10-cm calf section was 25.2 (7.0) Ω (the SFB2 instrument reads to one decimal place in the range 10 to 2000 Ω and the accuracy to within 1 %, claimed by the manufacturer, has been verified experimentally [20]). There are only slight discrepancies between MRI and anthropometry for most measures, except the circumference at calf A (anthropometry about 10 % lower) and calf cross-sectional areas (anthropometry, generally about 10 % higher).…”

“…Almost all published values for skin appear to be in the transverse direction across the skin. However, if alternative values for skin resistivity, at the extremes of the possible range of values considered here, were incorporated into the full equation (equation 1), estimates of muscle volume would be decreased by only 1.6 %, for a value of 2.89 Ω:m [20], and increased by 1.6 % if the value for stratum corneum ( 100 Ω:m) was applied. This is because the assessment of tissues in limb sections is dependent on the assumption of parallel arrangement of tissue resistances from which the fundamental BIA equation is derived as there may be conduction of current along at least some of the skin layers.…”

Optimizing electrode sites for segmental bioimpedance measurements

“…The variation in the relative values of the measured impedance parameters along the proposed equipotential lines was less than 1% and the maximum standard deviation of any measured relative impedance parameter in this study was 2%. However this variation includes both an instrumental variation of up to 1% and a biological variation (Ward et al 1997). The biological variation, particularly in ECW segmental volumes, over a period of 5 to 10 minutes upon becoming supine is significant and of the order of 2 to 4% (Thomas et al 1998).…”

Assessment of Bilateral Limb Lymphedema by Bioelectrical Impedance Spectroscopy

“…Generally, the default program settings were used for analyses; however, for some data sets, the analysis was optimized by adjustment of the frequency ''window'' used for fitting the data to the Cole model guided by minimizing the standard error of the estimate (SEE) for the curve fitting procedure. 16 The SEE for all analyses was less than 1%.…”