Bioimpedance assessment of hypohydration.

Abstract

This study examined the utility of bioimpedance spectroscopy (BIS) for assessing total body water (TBW) changes associated with moderate (6-7% TBW), hypertonic (HH), and isotonic (IH) hypohydration. The TBW of nine men was measured using BIS (TBWBIS) when euhydrated (EU) and during HH and IH. These measurements were compared with TBW measurements obtained using isotope dilution (deuterium oxide; TBWD20) during EU, and the estimated TBWD20 during hypohydration calculated from body weight change. Body weight loss was similar (P > 0.05) for HH (3.4 +/- 0.7 kg) and IH (2.9 +/- 0.7 kg). Plasma osmolality was higher (P < 0.05) on HH (292 +/- 4 mOsmol x kg(-1)) than EU (280 +/- 4 mOsmol x kg(-1)) and IH (284 +/- 3 mOsmol x kg(-1)), and higher (P < 0.05) during IH than EU. The measurements reflected a similar decrease (P < 0.05) in TBW during HH (TBWD20: 45.4 +/- 7.3 L, TBWBIS: 42.2 +/- 5.1 L) and IH (TBWD20: 45.8 +/- 7.5 L, TBWBIS: 42.0 +/- 4.9 L), compared with EU (TBWD20: 48.8 +/- 7.5 L, TBWBIS: 44.3 +/- 5.0 L), but TBWD20 was consistently higher (3.9 +/- 4.0 L, P < 0.05) than TBWBIS during all tests. TBWD20 and TBWBIS were correlated (P < 0.05) during EU (r = 0.87), HH (r = 0.84), and IH (r = 0.84). The change in TBW from EU during HH was greater (P < 0.05) for TBWD20 (3.5 +/- 0.8 L) than TBWBIS (2.1 +/- 0.9 L), but during IH the change in TBW reflected by TBWD20 (3.0 +/- 0.6 L) and TBWBIS (2.3 +/- 0.8 L) did not differ. The change in TBWD20 and TBWBIS between EU and hypohydration was correlated for HH (r = 0.77, P < 0.05), but not IH. These findings indicate that BIS is sufficiently sensitive to detect moderate hypohydration; however, the resolution of this technique diminished with isotonic fluid loss.