CAMBRIDGE, Mass. -- It resembles a cross between a trinket in a gumball machine and a space-age gizmo seen on Star Trek. Despite its curious appearance, this newly developed photosensor ring performs a serious task: It monitors the pulse rate and blood-oxygen level of ambulatory patients living at home.Previously, such tests required a visit to a clinic or, in some cases, were conducted by a visiting nurse.To remedy this, two Massachusetts Institute of Technology (MIT) researchers came up with the idea of developing a device that homebound patients could wear continuously, even in the shower. It had to be both compact and wireless. It also had to be completely noninvasive.With those criteria in mind, MIT research scientist Boo-Ho Yang and Professor H. Harry Asada designed a battery-powered ring that incorporates a light-emitting diode (LED) that continuously sends light into the finger, reflecting off the blood. When the heart beats, blood vessels contract and absorb more light. A photodiode captures the reflected light and converts it into an electrical signal. A tiny circuit then processes data from the photodiode, filtering extraneous information and transmitting the remainder to one of several receivers in the patient's home. The receivers transmit the signals to a computer at a telenursing center that analyzes the data to ensure the patient's pulse and blood-oxygen level are normal. In the event something is amiss, the computer automatically alerts doctors at a nearby medical center.Still in its prototype phase, the ring will be tested in coming months at an area hospital. One of the first obstacles to overcome, according to the researchers, is finding a way to make the device smaller. Currently the ring extends about an inch above the finger and is relatively bulky. A second version coming out later this year will be about the size of a class ring.Besides scaling back the ring's size, Yang and Asada foresee adding new LEDs and photodiodes to measure blood pressure and blood flow rates in the arteries. The researchers are also investigating ways to monitor patients outside the home by developing a portable control unit worn around the waist. The unit would include a small computer, modem and cellular phone that could interpret data from the finger ring and transmit information automatically to a hospital.While increased functionality and portability are important, the researchers' immediate goal is to make sure the rings provide consistently accurate readings. Dirt and sweat tend to skew results. Different skin colors also affect readings. As possible solutions, Asada is considering incorporating an array of LEDs and using spatial and temporal modulation. The group has developed another prototype of the ring for people of Asian descent, and others are possible.