A NEW METHOD FOR MONITORING HYDRATION AT HIGH-ALTITUDE BY BIOIMPEDANCE ANALYSIS

Our study evaluated the performance of a graphical method for monitori ng the fluid variation at high altitude in seven adult Caucasian male subjects (average age 25 yr, average height 177 cm). The graphical app roach is called the Resistance-Reactance (RXc) graph method and is bas ed on standard bioimpedance analysis (tetrapolar, 50 kHz frequency). M easurements were taken at sea level before the expedition, at 5050 m a fter 1 wk and 3 wk, and again at sea level after descent. Plasma and u rine electrolytes, osmolalities, and the free-water clearance were det ermined by standard methods. All climbers had baseline impedance vecto rs within the reference 95% tolerance ellipse for the Italian male pop ulation. The high altitude dehydration caused a significant lengthenin g of vectors, which after descent underwent a significant shortening a nd returned close to the baseline values. Average urine volume increas ed by 1.4 l . d(-1) in the first week and average body weight decrease d by 4.4 kg after 3 wk. The RXc graph method could be useful in the pl anning of the individual climber's appropriate dehydration and fluid i ntake at altitude since a feedback control of the hydration is allowed without any assumption of body composition.