DIGITAL MONITORING OF SLEEP-DISORDERED BREATHING USING SNORING SOUND AND ARTERIAL OXYGEN-SATURATION

A new portable digital recorder (SNORESAT) that uses the sound of snoring and arterial oxygen saturation (Sa(O2)) to monitor breathing abnormalities during sleep was constructed and compared in the laboratory with standard overnight polysomnography (PSG). The device digitally records sound from a transducer applied to the chest and Sa(O2) from a commercially available ear oximeter. A snore is identified when the moving time average of the sound exceeds a threshold voltage level longer than 0.26 s. The stored data are transferred to a personal computer for poststudy analysis. An analysis algorithm identifies a respiratory disturbance event when a quiet period of 10 to 120 s separates two snores and is associated with a fall in Sa(O2) exceeding 3%. The respiratory disturbance index (RDI), mean apnea duration, mean lowest Sa(O2), and number of desaturations > 3% are computed. A total of 129 referrals to the sleep apnea outpatient clinic underwent simultaneous all-night recording of PSG and SNORESAT Using the computed RDI recorded by the SNORESAT the sensitivity and specificity of the monitor in detecting sleep apnea syndrome (SAS) ranged between 84 and 90% and 95 and 98%, respectively, depending on the PSG value of RDI used to define SAS (range, greater-than-or-equal-to 7 to greater-than-or-equal-to 20 events/h). Using a PSG value of RDI greater-than-or-equal-to 10, or greater-than-or-equal-to 20 RD/h as the definition for SAS, the prevalence of SAS in the referral population was 45 and 31%, respectively. A positive diagnostic value from SNORESAT increased the probability of SAS in these patients to 95 to 96%, whereas a negative value from the SNORESAT decreased the post-test probability of OSA to 4 to 12%. We conclude that laboratory testing of SNORESAT indicates that the device can estimate the presence or absence of nocturnal breathing abnormalities with sufficient accuracy to be clinically useful in SAS.