"With real-time monitoring, the user can be continuously aware of his hydrocortisone levels, thus alerting him to dangerous levels of stress in the field," said David S. Lawrence, Ph.D., senior staff member and medicinal chemist at Johns Hopkins University's Applied Physics Laboratory. Stress evaluation is important to establishing and maintaining combat readiness among troops.
Lawrence said military commanders "would like to monitor the soldiers on the front lines (or in other stressful situations) to determine whether John Smith has reached his maximum stress load where he may become a danger to himself or to his unit. The commanders can then make a more informed decision as to the mission itself and Smith's role in it."
Such a device could have important civilian applications as well, with potential beneficiaries including pilots, air traffic controllers, deep-sea divers, and emergency medical personnel, among others.
The system is based on ongoing measurements of hydrocortisone, a steroid produced by the adrenal gland. Hydrocortisone regulates a number of biological functions and processes, and levels of the steroid in the bloodstream correlate with stress levels.
Bloodstream levels of the steroid fluctuate throughout the day, depending upon the time of day and factors such as diet and variations in metabolism. Thus any device that relies on hydrocortisone as an indicator must monitor its levels continuously.
Because taking constant blood samples is out of the question, Lawrence's team developed a device that could be linked to hydration systems like those used by serious cyclists and other athletes. These devices have a liquid-filled 'bladder' linked to a tube for hands-free drinking. The equipment allows a sensor constant access to the subject's saliva. Measurement of salivary hydrocortisone levels is thought to be an accurate indicator of the entire body's hormone concentration, said Lawrence.
The system relies on a class of polymers that contain a molecular imprint of hydrocortisone. The researchers create the imprint by growing the polymers in the presence of hydrocortisone and then removing the steroid, leaving behind an impression like a plaster cast.
Hydrocortisone molecules in saliva can move in and out of that impression, and the team has now designed a detector that shows a decrease in a fluorescent signal every time this happens. The signal change is proportional to the amount of hydrocortisone, allowing the device to track the molecule's levels over time. Lawrence hopes to have a demonstration system built by the end of September.
The Johns Hopkins University Applied Physics Laboratory's Institute for Advanced Science and Technology in Medicine provided funding for the work.
(This paper will be presented at 2:40 PM, Wednesday, May 29, in Assembly Room A in the Johnson Building at George Mason University.)