A COMPARISON OF SEGMENTAL AND WRIST-TO-ANKLE METHODOLOGIES OF BIOIMPEDANCE ANALYSIS

The common approach of bioelectrical impedance analysis to estimate bo dy water uses a wrist-to-ankle methodology which, although not indicat ed by theory, has the advantage of ease of application particularly fo r clinical studies involving patients with debilitating diseases. A nu mber of authors have suggested the use of a segmental protocol in whic h the impedances of the trunk and limbs are measured separately to pro vide a methodology more in keeping with basic theory. The segmental pr otocol hits not, however, been generally adopted, partly because of th e increased complexity involved in its application, and partly because studies comparing the two methodologies have not clearly demonstrated a significant improvement from the segmental methodology. We have con ducted a small pilot study involving ten subjects to investigate the e fficacy of the two methodologies in a group of normal subjects. The st udy did not require the independent measure of body water, by for exam ple isotope dilution, as the subjects were maintained in a state of co nstant hydration with only the distribution between limbs and trunk ch anging as a result of change in posture. The results demonstrate a sig nificant difference between the two methodologies in predicting the ex pected constancy of body water in this study, with the segmental metho dology indicating a mean percentage change in extracellular water of - 2.2%; which was not significantly different from the expected null res ult, whereas the wrist-to-ankle methodology indicated a mean percentag e change in extracellular water of -6.6%. This is significantly differ ent from the null result, and from the value obtained from the segment al methodology (p = 0.006). Similar results were obtained using estima tes of total body water from the two methodologies. (C) 1998 Elsevier Science Ltd. All rights reserved.