The change in blood and plasma volume following ingestion of glucose solutions of varying concentrations was estimated in twelve healthy male volunteers. Subjects consumed, within a 5 min period, 600 ml of a solution containing 0, 2, 5 or 10 % glucose with osmolalities of 0 (sd 0), 111 (sd 1), 266 (sd 7) and 565 (sd 5) mOsm/kg, respectively. Blood samples were collected over the course of 1 h after ingestion at intervals of 10 min. After ingestion of the 2 % glucose solution, plasma volume increased from baseline levels at 20 min. Plasma volume decreased from baseline levels at 10 and 60 min after ingestion of the 10 % glucose solution. Heart rate was elevated at 10 and 60 min after ingestion of the 10 % glucose solution and decreased at 30 and 40 min after ingestion of the 2 % glucose solution relative to the average heart rate recorded before drinking. It is concluded that ingestion of hypertonic, energy-dense glucose solutions results in a decrease in plasma and extracellular fluid volume, most likely due to the net secretion of water into the intestinal lumen.

The present study tested the hypothesis that multi-frequency bioelectrical impedance analysis (MFBIA) can be used to provide reasonable estimates of body mass, total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) at rest, during exercise-induced dehydration and subsequent recovery. Seven exercise-conditioned horses were administered indicators for measurement of resting TBW, ECFV and PV. MFBIA measurements at 24 frequencies between 5 and 280 kHz were obtained at rest, during prolonged submaximal exercise and for up to 13 h of recovery with food and water provided. Impedance–frequency response curves were described by a double-exponential decay equation from which coefficients were used, together with height and length, to generate predictive equations for estimating body mass, TBW, ECFV and PV. Predictive equations for body mass, ECFV and PV provided reasonable estimates of the parameter at rest and during exercise and recovery that were within 6% of absolute values determined using indicators. Despite the inherent error in estimating absolute volumes, the technique allowed accurate (within 1%) determination of the change in compartment volumes within individual horses over time. The number of frequencies at which impedance was measured could be reduced to seven without sacrificing the accuracy of the impedance–frequency relationships or the predictive equations – this enabled a 70% reduction in data-acquisition time (to ∼35 s) for each MFBIA measurement series. It is concluded that MFBIA can be used in individual horses to track changes in compartmental hydration status resulting from dehydration and rehydration.

The purpose of this study was to identify whether the central extracellular fluid volume status following and pypo- hypervolaemia can be measured by the initial distribution volume of glucose or by the extravascular lung water. These two estimates were compared with the initial distribution volume of sucrose which has been used as an indicator for the measurement of the extracellular fluid volume. The above three estimates were determined by the administration of glucose, chilled saline and sucrose solutions, before and after haemorrhage (30 mL kg−1), and subsequent fluid load (lactated Ringer's solution 90 mL kg−1). The distribution volumes of glucose and sucrose decreased after haemorrhage and increased after fluid load compared with normovolaemic values, and a linear correlation was obtained between these two distribution volumes (r=0.93, P<0.001, n=36). How ever, the extravascular lung water remained statistically unchanged throughout the procedure, despite a weak linear correlation with the sucrose distribution volume ( r=0.38, n=33, P<0.05). These results indicate that the initial distribution volume of glucose is more useful as an indicator of the central extracellular fluid volume status than the extravascular lung water.