Total body water estimation

Martinoh R, Mohamed El, Maiolo C et al. (2003) Total body water estimation using bioelectrical impedance a meta-analysis of the data available in the literature. Acta Diabetol. 40 Suppl 1 S203-6. 

Estimation of total body water (virtual tritium space) in the rat, cat, rabbit, guinea-pig, and man, and of the biological half-life of tritium in man,... 

The elimination half-life of Li+ is estimated at 24 hours, and more than 90% of the dose of Li+ is excreted into the urine. Renal clearance, however, is only 20%, since Li+ is actively reabsorbed in the proximal tubule at sites normally used for the conservation of Na. Thus, competition between Li+ and Na for uptake sites can alter the elimination of Li+ and its concentration in total body water. Na+ loading enhances Li+ clearance, while Na+ depletion promotes Li+ retention. This important relationship explains the appearance of Li+ toxicity (discussed later) associated with diet (low Na ),... 

The adult male human body contains about 60% (weight) of water and the adult female body about 50%. The large amount of body water is compartmentalized, each compartment being bounded by membranes. It has been estimated (Edelman and Leibman, 1959) that 55% of this water is contained within cells and that it is bounded by cell membranes. The remaining, extracellular water or fluids (ECF) is made up of a relatively small volume of plasma (7.5% of total body water in the vascular tree), with the remaining 37.5% in nonplasma and located outside the vascular... 

Since the doubly labeled water technique can be used to determine total body water, the method can be used to estimate the fat-free naass, as defined in the Obesity chapter. In brief, with a knowledge of the amount of total body water, and the assumption that normal subjects have a fat-free mass that is about 73% water, one can calculate the amount of fat-free mass. Further details are in the Obesity chapter... 

Estimated total body water (in liters) is calculated as a function of body weight 0.61/kg in children 0.6 and 0.51/kg in non-elderly men and women respectively 0.5 and 0.451/kg in elderly men and women respectively. 

It is an interesting question how toxic deuterium or heavy water is to humans. If it is accepted on the basis of animal experiments that the critical deuterium concentration (the double of which would cause severe physiological effects) is about 10%, then one can easily estimate that a person of 70 kg may drink 4.81 heavy water or 1.21 per day for 4 days without serious consequences (Forstel 1978). Thus, heavy water cannot be considered toxic to humans. This is an important conclusion, since stable isotopes (e.g., heavy water for the estimation of total body water) are widely used in clinical research and diagnosis (Krumbiegel 1991). In the literature, one can find also some more conservative estimates as far as the application risk of the deuterium in the form of heavy water is concerned, for example, Jones and Leatherdale (1991) suggest that the threshold for noticeable side-effects exists at the dosage between 70 and 140 g of 100% D2O. 

A variety of analytical methods have been employed for the estimation of deuterium in biological fluids in the context of total body water measurements. These include the falling drop method [241], freezing point elevation [242], infrared spectroscopy [243], gas chromatography [237] and mass spectrometry [240,244]. A range of accuracy between 0.5-5.0% is claimed from these various techniques in the overall protocol of body water measurement. 

To the clinician, the accurate measurement of total body water (TBW) can provide indirect information concerning whole body composition and energy balance. Desiccation measurements performed on eviscerated guinea pigs in 1945 [270] led to the almost universal acceptance of the fact that lean body mass (LBM) was of constant composition — and additionally, contained all of the body water. Thus the extracellular water associated with adipose tissue was neglected and the water content of lean body mass taken as 73.2%. The following simple formula, which was readily applied to man, provided an indirect estimate of body fat ... 

R. Kushner, Estimation of total body water by bioelectrical impedance analysis, The American Journal of Clinical Nutrition, vol. 44, pp. 417-424, 1986. 

Bioelectrical impedance (BI) measures the opposition (impedance) of biological tissues to the flow of alternating electric current. This opposition is highly correlated both with the concentrations of electrolyte ions and water in the tissues, as well as with their structure cell sizes, density, and spacing [1]. In the field of body composition, the technique is known as Bioelectrical Impedance Analysis (BIA), and it has been used for the estimation of total body water (TBW), fat-free mass (FFM) and fat mass (FM) [2]. Impedance is measured using a tetrapolar approach as described in [3]. 

Watson PE, Watson ID, Batt RD (1980). Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr 33(l) 27-39... 

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