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Ring monitors vital signs, location of patients in home

A ring developed by MIT engineers could allow caregivers and doctors to monitor a patient's vital signs in the home 24 hours a day.

A prototype of the ring, which contains miniaturized sensors and a wireless transmitter, measures pulse rate and the amount of oxygen in arterial blood. Other vital signs the researchers hope to measure in the future include blood pressure and blood flow rate in the arteries.

The ring, which can also estimate a patient's location inside his or her home, "is primarily for monitoring elderly people who live alone," said H. Harry Asada, Ford Professor of Engineering in the Department of Mechanical Engineering and director of the d'Arbeloff Laboratory for Information Systems and Technology. Other applications include monitoring patients who have been discharged from the hospital.

Professor Asada developed the ring with Dr. Boo-Ho Yang, a research scientist in the department. Data from the ring would be transmitted to small receivers installed in each room of a patient's home. The receivers, in turn, would be connected to a computer that analyzes the data and determines if anything seems amiss. If so, the computer would send a warning signal via the Internet to a hospital, alerting doctors to a potential problem.

While the system is currently designed for use in the home, the researchers are working to expand it to monitor patients outside the home as well. To allow such mobility, Professor Asada and Dr. Yang are developing a control unit that the patient would wear around the waist. The unit would include a small computer, a modem and a cellular phone. "The modem would turn the data read by the finger ring into data that can be transmitted by the phone to a hospital," Dr. Yang said.

The researchers developed the monitoring system with the following criteria in mind. "First, we wanted a device that a person wouldn't mind wearing 24 hours a day, even in the shower," Dr. Yang said. "That's why we decided on a ring." The device also had to be noninvasive, wireless, and compact.

The prototype ring extends about an inch above the finger and is relatively bulky. The researchers plan to make a second version this year that will be the size of a class ring. In all other respects, the prototype meets the design criteria.


Powered by a tiny battery, the ring works by manipulating light. First, a light-emitting diode continuously emits light into the finger. Some of that light is reflected off the blood in the finger, and is in turn captured by another element called a photo diode.

Pulse rate is one of the vital signs the ring can currently measure. "When the heart beats, the blood vessels expand a little bit, and they absorb more light," Dr. Yang explained. As a result, less light is reflected to the photo diode, so a weaker signal from the photo diode corresponds to a heartbeat.

The data from the photo diode are processed by a circuit in the ring that amplifies the signal. The circuit also "cleans" the signal, or removes extraneous data. The final signal is transmitted via an antenna embedded in the ring to the receiver in the room.

A home computer processes the signals to show not only the rhythm of the pulse rate, but also its shape. The latter "results in a graph that doctors can look at to diagnose a potential cardiac condition," Dr. Yang said.

The researchers expect that the ring could also be adapted to read other vital signs. For example, multiple LEDs and photo diodes could allow them to measure the speed of blood flow. This in turn could be analyzed to determine blood pressure.

In addition to reading vital signs, the monitoring system estimates a patient's location based on the strength of the signals captured by each receiver.

Dr. Yang and Professor Asada hope to conduct field tests of a more advanced ring at a local hospital. "We want to get feedback from patients," Dr. Yang said.

The researchers have applied for a patent on the ring. The work is sponsored by the Home Automation and Healthcare Consortium at the d'Arbeloff Laboratory. Professor Asada is principal investigator for the consortium; Ian W. Hunter, Hatsopoulos Professor of Mechanical Engineering, is co-PI. (Professor Hunter is also co-director of the D'Arbeloff Lab.)

A version of this article appeared in MIT Tech Talk on April 3, 1997.

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