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

A new portable digital recorder (SNORESAT) that uses the sound of snor ing and arterial oxygen saturation (Sa(O2)) to monitor breathing abnor malities during sleep was constructed and compared in the laboratory w ith standard overnight polysomnography (PSG). The device digitally rec ords sound from a transducer applied to the chest and Sa(O2) from a co mmercially available ear oximeter. A snore is identified when the movi ng time average of the sound exceeds a threshold voltage level longer than 0.26 s. The stored data are transferred to a personal computer fo r poststudy analysis. An analysis algorithm identifies a respiratory d isturbance event when a quiet period of 10 to 120 s separates two snor es and is associated with a fall in Sa(O2) exceeding 3%. The respirato ry disturbance index (RDI), mean apnea duration, mean lowest Sa(O2), a nd 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 s leep apnea syndrome (SAS) ranged between 84 and 90% and 95 and 98%, re spectively, depending on the PSG value of RDI used to define SAS (rang e, 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-tha n-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 d iagnostic value from SNORESAT increased the probability of SAS in thes e patients to 95 to 96%, whereas a negative value from the SNORESAT de creased 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 suf ficient accuracy to be clinically useful in SAS.