Plasma volume and blood viscosity during 4-hour sitting in a dry environment: Effect of prehydration

Doi T, Sakurai M, Hamada K, Matsumoto K, Yanagisawa K, Kikuchi N, Morimoto T, Greenleaf JE
Aviation, Space, and Environmental Medicine 2004; 75: 500-504

Purpose:
We examined our hypothesis that prehydration with an ion supply drink would be better than prehydration with water for maintaining the body fluid balance and preventing increased blood viscosity during a four-hour period spent sitting in a dry environment.

Methods:
Twelve healthy male subjects were studied in three randomized cross-over intervention trials of prehydration using an ion supply drink, water or a control condition with no prehydration. For each trial, subjects sat for four hours at an ambient temperature of 23.0-23.5℃ and a relative humidity of 18-36%. They consumed 6 mL/kg body weight of test beverage at the start of 4-hour sitting period. The plasma volume and blood viscosity were determined every hour. The urine volume and body weight were recorded at two and four hours.

Results:
The retention of the consumed fluid was significantly higher for ion supply drink than for water during the first two hours. The plasma volume decreased and the blood viscosity increased when there was no prehydration. The plasma volume for the ion supply drink was maintained at the baseline level in comparison to the water at two hours. The increase in blood viscosity for the patients in the ion supply drink was maintained at the baseline level which was significantly lower than the no prehydration at 2-3 hours.

Conclusion:
The ion supply drink may be useful for maintaining the body fluid balance and preventing an increase in blood viscosity during prolonged sitting in a dry environment.

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