ALTERATION OF THE EXTRACELLULAR AND TOTAL-BODY WATER VOLUMES MEASURED BY MULTIPLE FREQUENCY BIOELECTRICAL-IMPEDANCE ANALYSIS (MFBIA)

The extracellular fluid volume of rats was increased up to 33% by sequential injection of 4 ml aliquots of saline into the intraperitoneal cavity. Multiple frequency bioelectrical impedance analysis (MFBIA) measurements were used to monitor the changes in extracellular water (ECW) and total body water (TBW) after each aliquot. Using previously established prediction equations, changes in ECW and TBW determined by MFBIA were in very close agreement with the known induced volume changes (P<0.01). The resistivity of the body fluids was determined, and using a cross-validation procedure, measured volume changes were determined and compared with the known volume changes. The precision of MFBIA was demonstrated to be better than +/- 2 ml in a 350 g rat. The results confirm the validity, accuracy and precision of MFBIA in rats irrespective of gross alterations to their extracellular and total body water volumes.