In the first study of its kind, researchers from the University of Texas Health Science Center at Houston, the University of Houston and the Memorial Hermann Sleep Disorders Center evaluated the efficacy of remote infrared imaging in 13 men and women without known sleep apnea. They recorded the heat signals expired from the patients' nostrils or mouth using an infrared camera during one hour of polysomnography.

"Polysomnography is a diagnostic test, which establishes the presence or absence of sleep disorders," explained Jayasimha Murthy, lead author and assistant professor of medicine at the University of Texas Health Science Center. "Standard methods have the potential to significantly disturb a patient's sleep pattern, so what we see in the lab may not be a true representation of their sleep habits. However, remote infrared imaging is a non-contact method so there is minimal interference with the patient."

The infrared imaging technique works in a similar way to a traditional thermistor, in that it monitors the relative changes in airflow by measuring changes in the infrared heat signal. The biggest difference is that the thermistor is placed in the subject's nostril, whereas the infrared camera is situated six to eight feet from the patient's head.

"This system can be designed so that the patient isn't even aware that monitoring is taking place," said Murthy. "Also, this method allows us to have recorded data, so we can go back and extract the airflow data after the completion of the study, which we can't do with conventional sensors."

Upon completion of the polysomnography, the researchers compared the infrared imaging results with those obtained through conventional methods of sleep-apnea diagnosis, including nasal pressure, nasal-oral thermistors and capnography. Infrared imaging detected 20 sleep-disordered breathing events, compared with 22 events detected by the nasal-oral thermistor and 19 detected via nasal pressure.

Based on this outcome, the researchers postulate that infrared imaging offers near-perfect agreement with conventional methods and that the technique represents a non-contact alternative to standard nasal-oral thermistors. Murthy acknowledges that the work represents a preliminary stage of testing, but is optimistic about the future of infrared imaging for sleep-disorder diagnosis.

Murthy presented this work at CHEST 2007, the 73rd annual international scientific assembly of the American College of Chest Physicians, held last week in Chicago, IL. "The results from this study will greatly impact the development of this technology," he said. "While implementation of this technology for clinical studies is still far away, these early results are encouraging enough for us to pursue this further."