April 2, 2008 -- A new way to remotely monitor blood pressure, pulse rate and sweating could be used to screen for health signs as well as to administer lie detection tests on people without their knowledge or consent.
While researchers stress their work remains only proof-of-concept, a commercial version using sub-terahertz waves could theoretically help remotely monitor medical patients, evaluate athletic performance, diagnose disease and detect lies.
The key is in the surprising shape of human sweat ducts.
Recent advances in imaging technology revealed that sweat ducts, the tiny tubes that connect sweat glands to the outside of the skin, are helical -- or shaped like cork screws. That's a similar to the shape of some antennas.
"At this point it's not clear why nature chooses to create sweat ducts shaped like antennas," said physicist Aharon Agranat of the Hebrew University of Jerusalem and a co-author on a study about the work in the March 28 edition of Physical Review Letters. "We are simply exploiting it."
When Yuri Feldman, also a physicist at the Hebrew University of Jerusalem and a study author, saw these sweat gland images, they reminded him of the helical antennas often used in basic engineering classes.
By measuring certain factors like the number of twists, any beginning electrical engineering student can calculate which wavelength of energy the antenna would interact with, say the physicists.
The wavelength of human sweat glands falls in the sub-terahertz, or sub T-ray, range.
Full T-rays have recently been used in a variety of other applications, from uncovering hidden artwork to finding concealed weapons. T-rays, unlike their energetic cousins X-rays, are harmless.
By creating a machine that generates and detects sub T-rays, the scientists say they can look at which wavelengths interact with the millions of tiny "antennas" buried within the body's largest organ, the skin. While sweating doesn't produce T-rays, sweat production changes the wavelength that is bounced back off the sweat duct antenna.
By measuring these wavelengths, scientists can, in turn, calculate how much and where a person is sweating.
Different parts of the body sweat depending on the reason. Eating a spicy chili pepper causes sweat beads to break out on the forehead. Sunbathing causes sweat glands on the chest and back to be activated.
Various diseases and medical conditions activate other sweat glands, while also changing blood pressure and pulse rate. Eventually, with development of an accurate sweat map and other studies, the physicists hope to create a tool that can diagnose diseases based on where a person is sweating.
In subsequent tests the researchers were also able to also measure blood pressure and pulse rate remotely. They did this by monitoring the kinds of sweating that are directly linked to changes in blood pressure and pulse.
Currently the only way to measure blood pressure is by using an inflatable pressure cuff or a surgically implanted monitor. The only way to measure sweat is through a cumbersome process that uses electrodes on a small portion of skin. The new method can do both remotely and constantly.
While cautious about the new research, James Wolff, a doctor at Emerson Hospital in Concord, Mass. who was not associated with the study, said "this could open up a whole new area of research."
Because it has never been possible to remotely monitor sweat, pulse and blood pressure, no one has thought about what the the technique could be used for, said Wolff.
The device could also be used as a remote lie detector. A person could be subjected to lie detection without their knowledge or consent.
When a person lies, it triggers physiological responses: faster pulse, higher blood pressure and increased sweating. A polygraph machine measures these responses, but it has to be physically attached to a person.
Trained professionals can evade polygraphs, but if a person doesn't know they are being constantly tested the new method could be more effective.
Jonathan Marks, a professor of bioethics at Pennsylvania State University, says that lie detection using this method would still have problems with accuracy. A person already anxious over something else when they are being scanned could trigger a false positive.
"There are concerns about people's privacy," said Marks. "Is there a justification for screening people en masse for physiological data?
"Where would you do this?"
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