Dehydration is a frequent cause of morbidity and mortality in the elderly. Identifying at risk individuals and maintaining adequate fluid balance is an essential component of health care in aging population. Currently, there is no effective tool available to measure hydration status and distinguish those at risk. The reliability and validity o current hydration assessment methods and criteria such as thirst, skin turgor, blood pressure, pulse, urine output and specific gravity, MRI, dilution methods and bioimpedance, are limited; the methods are inaccurate or expensive. Given that dehydration is both preventable and reversible, the need for an easy-to-perform method for the detection of water imbalance is of the utmost clinical importance. The goal of this project is to develop and commercialize an inexpensive and easy-to-use device that monitors changes in hydration status and predicts at risk in home-bound and institutionalized elderly. The Hydration Monitor (HM) which is being developed under this grant can objectively quantify changes in the body water content and hydration status. The proprietary patented method implemented in the device is based on the experimental fact that ultrasound velocity through soft tissue is a linear function of the tissue water content. Because muscle provides the largest body reservoir for water, the assessment of water imbalance is conducted by measuring speed of ultrasound in muscle. In the course of Phase I studies we designed and assembled HM -prototype, extensively tested it on tissue phantoms and excised animal tissues. Based on the results of these tests we designed the HM -prototype for Phase II clinical studies. The aims of this Phase II SBIR project include building and bench-testing eight HM -prototypes and providing the prototypes to three sites for clinical validation. The objectives of human studies include: to determine normal daily variation of the individual hydration level in longitudinal study on elderly in assisted living facility; to assess range between individual hydration baselines for elderly in a normal physiologically hydrated state; to establish the ability of the HM to assess initial and corrected hydration status in a population of elderly patients admitted to the hospital for hypernatremic dehydration; to determine euhydration and dehydration thresholds when employing ultrasound velocity measures in parallel with conventional tests and to detect changes in the hydration status of young healthy adults before and after undergoing 3% acute dehydration; and to test the hypothesis that body dehydration is a generalized physiological process equally affected all body muscles by comparing the data obtained on calf and biceps muscles. The Phase II activities will culminate with developing a pre-production HM prototype and preparing comprehensive engineering documentation. The device will aim to comply with respective FDA Quality System Regulations, Good Manufacturing Practices and regulations which are incorporated into Artann Laboratories quality systems.