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சுருக்கம்

Small changes of hydration and Air Displacement Plethysmography

Coralie Lauley, Concepcion Gonzalez, Caroline Perlemoine, Henri Gin and Vincent Rigalleau

Background: Do current-life changes of hydration influence the assessment of small (~1kg) body composition changes by Air Displacement Plethysmography (ADP) ?

Methods: In ten normal subjects, ADP measurements were performed before and after the ingestion of 1.055L of water, and then after miction. The analysis were conducted with the subjects carriying external charges of 1.055L of oil (density 0.9), and 1.055L of a fat-free-mimicking solute (density 1.1).

Results: Ingesting and carrying 1.055L of water led to a similar significant increase in fat-free mass (ingested: +0.98±0.78 kg, carried: +1.01±0.98). A significant reduction of the body volume was detected after the miction (0.286±0.152L), without any significant change of body composition. In the three situations (basal-hydrated-after miction), fat and fat-free loads were discriminated, closest to reality in well-hydrated subjects. The measured changes were correlated with the true changes, but the %fat of the changes were underestimated (real: +22±34%, measured: -3±70%; p<0.001), and biased (Bland & Altman procedure): the more the change was fat, the less ADP underestimated its fatness.

Conclusions:ADP discriminates ~1kg alterations in fat vs fat-free mass. The analysis should be performed in similar conditions of good hydration.