PURPOSE: The use of nasal pressure as the sole monitor for airflow during polysomnography may overestimate disease, especially in mouth breathers. Remote infra-red imaging (IR-I) provides a non-contact method to monitor airflow. Using an infra-red camera placed eight feet from subjects and mathematical modeling, the heat signal from expired air is converted to a signal constituting an airflow channel and is integrated into the existing polysomnographic software as a separate channel. We evaluated the efficacy of IR-I as an alternative airflow channel during polysomnography in comparison with the conventional methods of nasal pressure, nasal-oral thermistors and capnography.
METHODS: Mean thermal measurements were performed continuously in real time at the nostrils or the mouth of subjects during one hour of polysomnography with simultaneous recording of nasal pressure, nasal-oral thermistor, expired CO2, IR-I, abdominal and thoracic excursion via piezocrystals and/or impedance plethysmography. To minimize bias, single airflow channel was scored separately without visualization of the other flow channels.
RESULTS: Thirteen subjects (9 men, 4 women) without known sleep apnea were studied. The range for age was 24 to 61 years, BMI:19.7 to 40.5 kg/m2, and Epworth Score: 1 to 19. 10.5 hours of sleep was recorded from 13 subjects. Flow-time trace generated by IR-I closely resembled that of the other airflow channels during sleep and wakefulness (figure 1). 22 sleep-disordered breathing events by thermistor, 19 by nasal pressure and 20 by IR-I were detected. One “false positive” event was detected by IR-I. The kappa statistic for thermistor versus IR-I was 0.90, nasal pressure versus IR-I was 0.76, thermistor versus nasal pressure was 0.87 (figure 2).
CONCLUSION: This is the first report of remote thermal imaging as a method to monitor airflow and detect airflow abnormalities during sleep. There was a near perfect agreement between remote IR-I and standard thermistors.
CLINICAL IMPLICATIONS: This novel “virtual thermistor” provides a non-contact method to aid in the diagnosis of sleep apnea and represents an alternative to standard nasal-oral thermistors and as an adjunct to nasal pressure.
DISCLOSURE: Jayasimha Murthy, No Product/Research Disclosure Information; No Financial Disclosure Information