Fluid imbalance can mean either volume depletion or volume overload, both of which affect cognitive and physical performance and cardiac maladaption. The number of hospitalizations for dehydration has increased steadily in recent decades, reaching 518,000 hospitalizations and $5.5 billion in hospital charges in 2004 . Congestion may arise from a variety of underlying conditions including renal failure and congestive heart failure (CHF). CHF is a chronic, age-related disease with an estimated 670,000 new cases per year. CHF patients took up 6.5 million annual hospital days and represented $39.2 billion in health costs (of which hospital costs accounted for 60%) in 2010 .
Fluid imbalances (e.g. dehydration, congestive heart failure, etc.) are prime examples of conditions preventable from hospitalization if they are diagnosed and managed early. Unfortunately, an individual’s fluid status is difficult to assess and there is no single, universal gold standard to inform decision making . This project appeals to the need for a rapid, accurate, non-invasive, portable, and safe technique to measure volemic state, particularly in an outpatient setting. Such an invention could be used in monitoring and treatment of the elderly, CHF patients, athletes, and military personnel, among many other populations.
There is no single robust “gold standard” method to determine hydration state. Often, multiple metrics are used in combination to provide a more complete assessment of hydration state. The most widely used metrics include: body mass change, plasma osmolality, % plasma volume change, urine osmolality, urine specific gravity, urine conductivity, urine color, total body water (dilutional), total body water (bioelectric impedance) [4,5]. Though various tools and metrics exist, they are plagued with issues including high variability, being easily confounded, and being indeterminant as a stand-alone measurement.
We are designing and building noninvasive, portable, nuclear magnetic resonance (NMR)-based sensors that are capable of detecting fluid status. Proton NMR is a technique to obtain information about water in a tissue based on T1 and T2 relaxation times. We have shown that proton NMR, where hydrogen functions as a proxy for water, demonstrates relaxometry changes that reflect underlying water volume and distribution changes in animals [6, 7]. We believe that miniaturized NMR sensors are a suitable diagnostic platform for assessing hydration state in patients.
 S. Kim, Preventable Hospitalizations of Dehydration: Implications of Inadequate Primary Health Care in the United States. Annals of Epidemiology, vol. 17, no. 9, p. 736, Sep. 2007.
 Sieck, S. The Economics and Reimbursement of Congestive Heart Failure, Chapter 2. 2012.
 S. a Kavouras. Assessing hydration status. Current opinion in clinical nutrition and metabolic care, vol. 5, no. 5, pp. 519–24, Sep. 2002.
 Carter R, Cheuvront SN, Kolka MA, Sawka MN. Hydration Status Monitoring. Book Chapter – National Academy of Science (2004).
 Armstrong LE. Assessing Hydration Status: The Elusive Gold Standard. Journal of the American College of Nutrition. 26:5755-5845 (1997).
Fig 1. Schematic of early version NMR sensor against patient leg.
Fig 2. Magnetic field profile lines from magnet array design.
Fig 3. Single-sided sensors like the commercially-available NMR MOUSE (Mobile Universal Surface Explorer) can probe any part of the body.