Dehydration, or the loss of body water, is a common health problem during military operations, athletic events and illness, particularly in children and the elderly. Warfighters frequently become dehydrated when training or fighting in hot and mountainous environments because heat and high altitude increase body water losses. The negative consequences of dehydration worsen as body water losses increase. Severe dehydration (>10%) is a life-threatening emergency that may result in heat illness, seizures, permanent brain damage or death. The most common type of dehydration is caused by sweat loss during heavy physical labor or exercise (hypertonic dehydration). A different type of dehydration can be caused by blood loss, burns, diarrhea, vomiting or diuretic drugs used for example by diabetics (isotonic dehydration). Despite the critical importance of proper fluid balance to human performance and health, no field-expedient, non-invasive dehydration test is available for either form of dehydration. The ultimate goal of this project is to develop a field-expedient, non-invasive test for both types of dehydration. The test will be sensitive to 2% dehydration, a critical threshold for performance impairment and a statistically valid decision point for hydration assessment.
Design: Fifteen volunteers will be first euhydrated (well-hydrated) and then moderately dehydrated (2-4%) using two procedures. First, sweat loss during exercise in the heat without fluids (hypertonic dehydration). Second, excessive urination stimulated by a diuretic pill called Lasix (isotonic dehydration). SRP biomarkers in saliva samples will be compared to changes in body weight, and to known hydration indicators in blood and urine. Results will identify the best SRP biomarkers for diagnosing both types of dehydration and compare accuracy of the new saliva test to the existing hydration indicators.