Effect of body positions and splints in bioelectrical impedance analysis

The objective of this study was to evaluate body composition as measured by bioelectric impedance analysis using splints and body positions differing from the standard supine position. Forty-three patients, randomized into two groups of different body positions, and 101 healthy volunteers were prospectively studied. Resistance and reactance of body tissues were measured by bioelectric impedance analysis. Body composition is described by a three-compartment model composed of body fat, body cell mass, and extra cellular mass. The patients were measured in the standard supine position and then randomized into two groups. They were then remeasured with the appropriate splinting device or position change. Volunteers were measured in the standard supine position and all four alternative positions. There was a statistically significant difference demonstrated in whole body resistance, whole body reactance, body cell mass, and the ratio of extracellular mass to body cell mass in some body positions. The percentage of change with different body positions and splints, when compared with the standard supine position, was generally below 2%, a clinically insignificant difference. We conclude that the reliability of resistance and reactance as measured by bioelectric impedance analysis is clinically valid using any of the tested body positions and/or splints. The three-compartment model may be a useful concept to measure body composition changes in both healthy and sick persons.