Tracheal sound analysis for detection of sleep disordered breathing

This study aimed to investigate whether the combination of tracheal sounds and nasal pressure sensor (TS-NP) allows the same detection of apneas and hypopneas as the recommended American Academy of Sleep Medicine (AASM) method for obstructive sleep apnea (OSA) diagnosis, i.e., the combination of an oronasal thermistor and nasal pressure sensor (Therm-NP). Polysomnographic recordings of 33 patients (6 females; mean age 52.9 ± 10.3 years; mean body mass index, BMI, 30.0 ± 5.2 kg/m 2 ) were analyzed to compare detection of apneas by two different methods of combined airflow signals: a) Therm-NP and b) TS-NP. The two scoring methods were performed randomly and independently of each other. Respiratory event detection results and apnea–hypopnea index (AHI) obtained using Therm-NP signals as a reference were compared to those obtained by TS-NP signals. The number of respiratory events scored using Therm-NP was 7268, while it was 7329 with TS-NP. The sensitivity and positive predictive value of TS-NP with respect to Therm-NP were 93.0 and 90.6, respectively. The average AHI for all patients was 29.8 ± 22.9 for Therm-NP and 30.0 ± 22.6/h for TS-NP. With the Therm-NP as a reference detection, a kappa statistic value of 0.86 for TS-NP revealed a high agreement for classifying OSA into the severity classes mild, moderate, and severe. However, 55% of total events scored by Therm-NP were hypopneas while 59% of events scored by TS-NP were apneas. These results show that TS-NP reliably detects the same number of respiratory events as Therm-NP, despite a difference in the apnea to hypopnea ratio between the two methods. The use of TS does not modify AHI calculations and guarantees accurate sleep apnea diagnosis and severity assessment. Thus, TS can be used as a substitute for an oronasal thermistor in sleep recording systems.