KOULMANN, N., C. JIMENEZ, D. REGAL, P. BOLLIET, J.-C. LAUNAY, G. SAVOUREY, and B. MELIN. Use of bioelectrical impedance analysis to estimate body fluid compartments after acute variations of body hydration level. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 857–864, 2000. Physiological measurements including body mass, plasma osmolality, natremia, plasma volume measured by Evans Blue dilution, and total body water (TBW) and extracellular water (ECW) volumes estimated by bioelectrical impedance analysis (BIA) were recorded in eight healthy young Caucasian subjects before and after acute variations of their body hydration state on four separate occasions: 1) euhydration or control trial (C); 2) heat-induced dehydration of 2.8% body mass (D); 3) exercise-induced dehydration of 2.8% body mass (E); and 4) glycerol-hyperhydration (H). Heart rate, rectal and mean skin temperatures were also recorded throughout the experiment. The main result of the study is that BIA only half predicted the body water loss after exercise, although conditions were standardized (electrode placement, side of the body, limb position, posture, and ambient temperature). Differences in body temperatures cannot explain such an unexpected result, nor did the study of plasma osmolality and sodium concentration. If BIA appears to adequately predict changes in TBW after heat-induced dehydration and glycerol hyperhydration, further studies including measures of TBW and ECW by dilution tracer methods would be necessary to establish the validity of using the BIA method to measure such changes and to interpret ECW variations.
When exposed to heat stress, whatever it is, metabolic and/or thermal heat, men may lose a considerable amount of body water through sweating, induced by the regulation of body temperature. As soon as 1947, Adolph et al. (1) reported that body fluid compartments contribute in different extent to the water loss. However, only a few data are available concerning the distribution of the water loss among body fluid compartments; the alterations in different compartmental fluid status would depend on both the kind of heat stress applied (12) and the level of hypohydration (25). On the other hand, hyperhydration induced by glycerol ingestion before exposure to dehydrating events appears to be a potential countermeasure to the deleterious effects of hypohydration (15,20). Only one study (23) reported the changes in the interstitial fluid volume due to the increase of total body water. During those studies, body fluid compartments were determined using tracer methods, including radioactive tracers. The dilution techniques were indeed the method used until recently to assess total body water and fluid compartment volumes. However, repeated measurements using the dilution methods were difficult, because they required either a waiting period while the tracers cleared from the body, or the use of higher doses. Moreover, the repeated use of radioactive tracers appeared now to be questionable, especially in young healthy subjects for experimental design.
Recently, there has been considerable interest in bioelectrical impedance as a safe, convenient, and portable method of estimating body composition, associated with high reliability in normal individuals (2) and the ability to perform frequent, rapid, and noninvasive measurements. The aim of the present study was then, using bioelectrical impedance analysis (BIA), to estimate changes in body fluid compartments after different acute changes in the body hydration level—heat-induced dehydration, exercise-induced dehydration, and glycerol hyperhydration. Because a great variety of factors other than body composition, as electrode placement, side of the body, limb position (2), body posture (21,24), ambient and skin temperatures (3,8), plasma osmolality and sodium concentration (8,21) could, at least potentially, alter BIA measurements, we have particularly taken care to standardize our experimental design and to respect the manufacturer’s recommendations.