OAK RIDGE, Tenn., April 29, 1997 -- A chip that fits your fingertip may someday measure and transmit your body temperature when you're ill. An array of chips attached to your body may obtain and send additional information on your blood pressure, oxygen level and pulse rate to your doctor miles away.
Such "medical telesensors" - application-specific integrated circuits that measure vital signs, process the data and transmit it as radio signals to a remote receiver - are being developed at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) for military troops in combat zones. Using funding from the Defense Sciences Office of the Defense Advanced Research Projects Agency (DARPA), a group led by ORNL researcher Tom Ferrell has built a temperature sensor 2.3 millimeters on a side (about one-eighth the size of a postage stamp). The chip can be attached to a finger or placed in an ear. There, it can measure body temperature and transmit a reading when queried by a remote receiver.
"Military leaders need a way to find out quickly which soldiers have been wounded and what their conditions are," Ferrell says. "Then, medics will be able to decide whom to treat first and whom to remove from the battlefield for treatment at hospitals. The first objective is to get the least seriously injured treated so they can return to combat."
The ultimate research goal is to develop an array of chips to monitor body functions collectively. These chips may be attached at various points on a soldier using a nonirritating adhesive like that used in waterproof adhesive bandages. Such medical telesensors will send physiological data via wireless transmission to an intelligent monitor on a medic's helmet. The monitor will alert the medic if the data show that the soldier is in trauma. The monitor also could receive global satellite positioning data to help the medic locate wounded soldiers.
Medical telesensors developed for DARPA are expected to have civilian applications, so ORNL is seeking additional funding from the private sector.
"Wireless monitors attached to the skin," says Ferrell, "could provide valuable information on the physiological condition of intensive-care patients in hospitals, high-risk outpatients, infants at risk of suffering sudden infant death syndrome, and police, firefighting and construction personnel in hazardous situations."
The temperature-measuring chip was designed under Ferrell's leadership by a group at the University of Virginia. This work relied in part on earlier work by ORNL scientist Alan Wintenberg, Chuck Britton and others.
The chip contains a temperature sensor that measures absolute temperature using bipolar transistors whose electronic properties are sensitive to temperature. These components are all incorporated on a single chip together with analog signal processing, transmission electronics and an antenna that sends the data by radio signals (radio frequency transmission) to a monitor when the chip is queried.
Each chip, Ferrell says, is planned to have a unique identifier - a characteristic radio signal pattern in which the frequency spectrum changes every few microseconds. Such spread-spectrum transmission allows the monitor to know which soldier needs immediate medical care. In addition, thin-film lithium-ion batteries developed by John Bates of the Solid State Division could be used to supply the very low levels of power required by the circuit.
The ORNL group, which also has collaborated with several faculty members from the University of Tennessee, including Don Bouldin, Jim Rochelle and Paul Crilly, is now developing a pulse oximetry sensor for DARPA. This device, ultimately to be fabricated on a single chip, will measure pulse rate and blood oxygen level. Blood oxygen level can indicate a wide variety of respiration-related problems. The group plans to develop another type of pulse sensor and a blood pressure sensor, in addition to a device that measures electrical conductivity in the skin, an indicator of stress.
"Measurements of pulse rate are important to the military," Ferrell says, "because this information helps medics quickly determine which of the wounded soldiers are alive and which are dead. Also, blood pressure can be determined by measuring and comparing times of pulse arrival at various points on the body. Measurement of a drop in blood pressure is important because that may indicate a soldier is bleeding." A pulse sensor also has civilian uses; for instance, measurements of erratic pulse rate can warn that a patient has cardiac arrhythmia.
The pulse oximetry sensor will measure the pulse on the wrist or neck by use of an optical pressure sensor. To measure changes in blood oxygen level, the sensor detects changes in hemoglobin, the iron-containing pigment in red blood cells. When the oxygen level changes, the color of the hemoglobin is altered. Such a chip will have an infrared light source and detector that can measure changes in the light absorption of the hemoglobin when it is excited by light of specific frequencies. The measurement results are reported by wireless telemetry.
ORNL, one of the Department of Energy's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Research Corporation.