Infrared imaging for sleep apnea diagnosis shows promise

Sleep apnea is commonly diagnosed by way of measuring airflow by nasal pressure, temperature, and/or carbon dioxide, through sensors placed in the nose. However, this method is uncomfortable to some and can potentially disturb sleep. But new research, presented at CHEST 2007, the 73rd annual international scientific assembly of the American College of Chest Physicians (ACCP), shows that remote infrared imaging can monitor airflow and accurately detect abnormalities during sleep, without ever coming in contact with the patient. The study indicates that the new method is ideal because it is portable and can monitor sleep in a natural environment.

“Polysomnography is a diagnostic test, which establishes the presence or absence of sleep disorders. But 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 the patient’s sleep habits,” said lead study author Jayasimha Murthy, MD, Assistant Professor of Medicine, University of Texas Health Science Center at Houston, TX.

“However, remote infrared imaging is a noncontact method, so there is minimal interference with the patient. In fact, this system can be designed to where the patient isn’t even aware that monitoring is taking place.”

In the first study of its kind, Dr. Murthy and his colleagues from the University of Texas Health Science Center at Houston, the University of Houston, and Memorial Hermann Sleep Disorders Center in Houston, TX, evaluated the efficacy of remote infrared imaging (IR-I) in 13 men and women without known sleep apnea. Researchers recorded the heat signals expired from patients’ nostrils or mouth using an infrared camera during 1 hour of polysomnography. To minimize any bias, airflow channels were recorded and analyzed separately. Results were then compared with those obtained through the conventional methods of sleep apnea diagnosis, including nasal pressure, nasal-oral thermistors, and capnography.

“The underlying principle of monitoring the relative changes in airflow based on the changing of the infrared heat signal is similar to that of the traditional thermistor,” Dr. Murthy explained. “However, the biggest difference is that the thermistor is placed in the subject’s nostril while the infrared camera is placed 6 to 8 feet from the patient’s head. 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, results showed that IR-I detected 20 sleep-disordered breathing events, compared with 22 events detected by the nasal-oral thermistor, and 19 events detected by nasal pressure. Given the outcome, researchers suggest that IR-I was in near-perfect agreement with conventional methods and that it represents a noncontact alternative to standard nasal-oral thermistors. Though Dr. Murthy acknowledges that this study represents a preliminary stage of testing, he is optimistic about the future of infrared imaging for sleep disorder diagnosis.