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MIT Ring Monitors Patients' Vital Signs

CAMBRIDGE, Mass.-A ring developed by MIT engineers could allow caregiversand 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 awireless transmitter, measures pulse rate and the amount of oxygen inarterial blood. Other vital signs the researchers hope to measure in thefuture include blood pressure and blood flow rate in the arteries.

The ring, which can also estimate a patient's location in a home,"is primarily for monitoring elderly people who live alone," said H. HarryAsada, Ford Professor of Engineering in the Department of MechanicalEngineering and director of the d'Arbeloff Laboratory for InformationSystems and Technology. Other important applications include monitoringpatients who have been discharged from the hospital.

The ring and other health-care devices in development at MIT weredemonstrated at a recent MIT Workshop on Healthcare Robotics chaired byProfessor Asada and sponsored by the National Science Foundation.

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

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

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

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

Powered by a tiny battery, the ring works by manipulating light.First, a Light-Emitting Diode (LED) in the ring continuously emits lightinto the finger. Some of that light is reflected off the blood in thefinger, and is in turn captured by another element called a photo diode.

Pulse rate is one of the vital signs the ring can currentlymeasure. "When the heart beats, the blood vessels expand a little bit, andthey absorb more light," Dr. Yang explained. As a result, less light isreflected to the photo diode, so a weaker signal from the photo diodecorresponds to a heartbeat.

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

A home computer processes the signals to show not only the rhythmof the pulse rate, but also its shape. The latter "results in a graph thatdoctors can look at to diagnose a potential cardiac condition," Dr. Yangsaid.

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

In addition to reading vital signs, the monitoring system estimatesa patient's location in the home based on the strength of the signalscaptured by each receiver.

Dr. Yang and Professor Asada hope to conduct field tests of a moreadvanced 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 issponsored by the Home Automation and Healthcare Consortium at thed'Arbeloff Laboratory. Professor Asada is principal investigator for theconsortium; Ian W. Hunter, Hatsopoulos Professor of Mechanical Engineering,is co-PI. (Professor Hunter is also co-director of the D'Arbeloff Lab.)

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