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

The extracellular fluid volume of rats was increased up to 33% by sequ ential injection of 4 ml aliquots of saline into the intraperitoneal c avity. Multiple frequency bioelectrical impedance analysis (MFBIA) mea surements were used to monitor the changes in extracellular water (ECW ) and total body water (TBW) after each aliquot. Using previously esta blished prediction equations, changes in ECW and TBW determined by MFB IA 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 wa s demonstrated to be better than +/- 2 ml in a 350 g rat. The results confirm the validity, accuracy and precision of MFBIA in rats irrespec tive of gross alterations to their extracellular and total body water volumes.