DOES MULTIFREQUENCY BIOELECTRICAL-IMPEDANCE RELATE TO BODY-COMPOSITION

Background: There is need for a rapid, noninvasive, inexpensive yet ac curate bedside technique to measure body composition. Bioelectrical im pedance analysis measures the resistance and conductance of a weak ele ctrical current passed through the body. It has been suggested that mu ltifrequency impedance analysis can determine the distribution of flui d between the extracellular and intracellular compartments. Materials and Methods: The correlation between the resistance signals obtained f rom multifrequency bioelectrical impedance measurements and body compo sition was determined in normal rats ranging from 150 to - 400 g in we ight. Total body water, body fat, total body sodium, and total body po tassium were measured using the carcass analysis technique, and extrac ellular water was derived from a dilutional marker using sodium bromid e. Fat-free mass was calculated as the difference between body weight and body fat, and intracellular water was derived from total body wate r and extracellular water. Multifrequency bioelectrical impedance was measured at frequencies ranging from 3 to 300 kHz. Resistance at zero frequency and infinite frequency was calculated using the Cole and Col e equation. Results: Resistance index (i.e., length of the animal(2)/r esistance) was highly correlated with all body compartments (r = 0.879 -0.996) at all frequencies. There was also a high correlation among al l compartments of the body (r = 0.971-0.999). Because of this high int ercorrelation among the body compartments, a specific relationship bet ween the multifrequency bioelectrical impedance signal and a specific compartment was not identified. Conclusions: Resistance index at any f requency will be correlated with any body compartment in a normal popu lation. The utility of this technique should be determined in situatio ns where there is a disturbance in the relationship between various co mpartments of the body. (C) 1996 Academic Press, Inc.