HOUSTON – (October 1, 2002) – Whether 240 miles above in the International Space Station or firmly grounded on Earth, medical testing without needles wins everyone's vote.
Refinements under way to current near infrared (NIR) spectroscopic techniques will expand the range of non-invasive blood and tissue chemistry measurements. These changes also will provide accurate readings unaffected by skin color or body fat.
"Once complete, this device will allow chemical analysis and diagnosis without removing samples from the patient. It will be useful for monitoring surgery patients, assessing severity of traumatic injury, and evaluating injuries in space," said Dr. Babs Soller, researcher on the National Space Biomedical Research Institute's smart medical systems team.
Patients may now encounter NIR spectroscopy at the doctor's office. The pulse oximeter, used for measuring oxygen saturation, employs a small clip placed on the finger or ear to measure the amount of oxygen carried by the blood, along with pulse rate.
"Light in the near infrared region has slightly longer wavelengths than red light. It is important for medicine because those wavelengths, for the most part, actually pass through skin and to some extent bone, allowing you to get chemical information about tissues and blood," said Soller, a research associate professor of surgery at the University of Massachusetts Medical School.
To refine the technology for more varied measurements, Soller and colleagues are gathering data from patients. Study participants include cancer, cardiac surgery and trauma patients.
"We're measuring hematocrit, tissue pH and tissue oxygenation using our device and standard techniques," she said. "These data will give us the information needed to derive equations to calibrate the new NIR instrument."
The blood and tissue measurements will provide key information, such as whether a patient is anemic and whether there are adequate levels of oxygen and blood flow to muscle tissue cells.
To make the device accurate regardless of skin color or body-fat content, Soller's group is gathering data from 100 subjects representing five ethnic groups – African-American, Asian, Caucasian, Hispanic and Mediterranean.
"NIR light is absorbed by pigment in darker skin, so we are collecting data and developing equations that remove the influence of skin color and fat content on measurements," Soller said. "Our technique will take this human variability into account. Once we adjust for these variables, we can take measurements on the arm or leg or even sew sensors into clothes."
The final step will be to develop clinical guidelines for the measurements, so that physicians know the significance of the readings.
"Tissue pH and oxygenation are new medical parameters, so we have to determine specific values that, based on the readings, allow us to identify when a person is in shock or in need of treatment. We also see this device as a means to assess the adequacy of the treatment employed," Soller said.
Since the technology is being designed to meet the lightweight, low-power and portable requirements of the space program, it will also be useful in ambulances, helicopters and emergency rooms.
"The beauty of the non-invasive technique is that it allows physicians to take measurements continuously, once a second if you want," she said. "We think these measurements might help prevent serious complications from traumatic injuries by providing early indications of low oxygen availability."
Soller feels the device will be particularly useful for treating patients with shock caused by excessive bleeding or heart attack, patients with internal bleeding, and pediatric patients, where it can be difficult to take multiple blood samples.
The technology also has potential use in exercise and endurance training.
"Tissue pH can measure how hard a person's muscles are working. The device could be used to determine when the muscles are exhausted, so you could use it to develop a personal training program," she said.
The prototype device currently uses two optical fibers, one shining the light into the patient and the other carrying the reflected light back to a device that analyzes the data. However, it still needs to be smaller for space use.
"We're actively looking for a commercial partner to build a miniature version of the device," she said.
The NSBRI, funded by NASA, is a consortium of institutions studying the health risks related to long-duration space flight. The Institute's 95 research and education projects take place at 75 institutions in 22 states involving 269 investigators.
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