Simple Impedance Measurement Detects Dehydration

A redesigned medical device that monitors a person's hydration level could improve survival odds for people medically at risk from dehydration or congestive heart failure (CHF).

Scientists at the Oak Ridge National Laboratory (ORNL, TN, USA) improved and miniaturized an existing device called The ZOE Fluid Status Monitor, used primarily in home health care applications, in order to improve the product by making it more robust, smaller, less expensive, and capable of remote monitoring. The ZOE device measures thoracic Zo (base impedance)--a measurement of the electric current traveling from the top to the bottom of the thorax. This is accomplished by placing one electrode at the top and another at the bottom of the breastbone. The smaller the resistance (measured in ohms) the more fluid is inside the chest cavity. The normal range for humans is between 19 ohms and 30 ohms; values lower than 19 indicate that a person may be overhydrated, while values exceeding 30 indicate dehydration. A wearable wireless version of the ZOE instrument, ZOEwi, will allow monitoring during activity and is planned for market introduction in 2008. The ZOE is a product of Noninvasive Medical Technologies (Las Vegas, NV, USA).

"Studies have shown that up to 80% of troops become dehydrated while performing their duties, and that's a major concern to the military because the soldiers are not able to perform at peak levels,” said Katy DeMarr, vice president of government relations at Noninvasive Medical Technologies. "Similarly, high school and college athletes would benefit greatly from knowing their hydration levels.”

Dehydration symptoms generally become noticeable after 2% of one's normal water volume has been lost, and include thirst, decreased urine volume, abnormally dark urine, tiredness, lack of tears, headaches, dry mouth, and dizziness when standing due to orthostatic hypertension. As dehydration increases, symptoms worsen. With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle, vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses greater than 15% are usually fatal.


Related Links:
Oak Ridge National Laboratory
Noninvasive Medical Technologies