#REVIEW INTRACELLULAR EXTRACELLULAR BODY FLUID COMPARTMENTS FREE#
Body density was used to calculate fat free mass with the Siri formula (22). The percentage of body fat of each subject was determined by hydrostatic weighing (20) and a determination of residual lung volume with a bell spirometer. The test protocol was approved by the Institutional Review Board at the University of Connecticut and complied with the policy statement regarding the use of human subjects as published by Medicine and Science in Sports and Exercise. Thirteen healthy male college students (Table 1) gave their written, informed consent to participate in this study after all risks and procedures had been explained. We hypothesized that volumes derived via BIS would be statistically different from those derived with tracer dilution. This was accomplished by using deuterium oxide and sodium bromide dilution techniques as reference measures.
Therefore, the purpose of this investigation was to test the validity of a technique that provides TBW, ECV, and ICV estimates from BIS analyses. These limitations emphasize the need for validation studies.īecause BIS methods and commercial instruments have been developed only during the present decade, the validities of BIS modeling techniques have not been firmly established (23). Third, BIS is linked with TBW, ECV, and ICV by theory (7,8,12,14), not proven biophysical principles (17). Second, the following factors are known to affect impedance measurements: electrode placement, side of the body, posture, limb position, composition of the examination surface, ambient temperature, hydration status, food and liquid intake, plasma osmolality, and recency of exercise (4,17,23). First, BIS in humans is likely to be influenced by differences in body composition (17,29). However, three limitations of the BIS technique are relevant to this investigation. Bioimpedance spectroscopy (BIS) is a statistical modeling technique (7,9,29) that extrapolates values for resistances at very high and very low frequencies from resistance values in the frequency range that is reliable (i.e., 1-500 kHz), then calculates ECV, ICV, and TBW (29). Single-frequency bioelectrical impedance values predict TBW well (r = -0.86, P 500 kHz) frequencies (8,29), statistical modelling techniques have been used. Bioelectrical impedance analysis is based on the assumption that electricity (i.e., a low level alternating current, single 50 kHz frequency) is conducted poorly by fat and bone but is conducted well by tissues that contain predominantly water and electrolytes. A corrected bromide space can be calculated from the serum bromide concentration after administration of a known quantity of bromide this is an excellent approximation of ECV (10).ĭuring the 1980s, single frequency bioelectrical impedance analysis became a widely-used technique for measuring TBW (12,17). Historically, extracellular fluid volume (ECV) was measured with thiocyanate and isotopes of sodium and chloride (i.e., 24 Na, 22Na, 36Cl), but in recent years bromide has been the most widely used tracer in research studies (12,15,16). TBW has been measured reliably by using the isotopes of tritium, hydrogen, and deuterium (i.e., 3 H 2O, 2H 2O, H 2 18O ref. Medicine and science require precise, reliable techniques to assess total body water (TBW) and fluid compartment volumes.
We concluded that BIS is valid for between-subject comparisons of body fluid compartments, is appropriate in clinical settings where change in ECV/ICV ratio is important, and should be used by comparing the required level of accuracy to the inherent technique error/variance. The correlation coefficients of dilution versus BIS volumes (r = 0.93 to 0.96) were significant at P < 0.0001 SEEs were: TBW, 2.23 L ECV, 1.26 L and ICV, 1.71 L. Electrode placement, posture, exercise, food/fluid intake, and ambient temperature were controlled. Impedance was measured (50-500 kHz) at rest, on a nonconducting surface, with a BIS analyzer. Thirteen healthy males (mean ± SD: age, 23 ± 3 yr body mass, 80.6 ± 14.7 kg) had their TBW and ECV measured by ingesting dilution tracers (7.27 g deuterium oxide, 1.70 g sodium bromide blood samples at 0 and 4 h). The purpose of this study was to test the validity of a multiple frequency bioimpedance spectroscopy (BIS) technique that estimates extracellular fluid volume (ECV), intracellular fluid volume (ICV), and total body water (TBW). Bioimpedance spectroscopy technique: intra-, extracellular, and total body water.
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