Comparison of apnea-hypopnea indices determined by using the combinations tracheal sound/nasal pressure sensors and thermistor/nasal pressure sensors

Objective: To show whether the combination of tracheal sounds and nasal pressure sensors (TS/NP). allows the same detection of apneas and hypopneas as the combination of oronasal thermistor and nasal pressure sensors (Therm/NP), the recommended AASM method. Materials and methods: Polysomnographic recordings of 34 patients (6 females, mean age 52.9 ± 10.3 years, and mean BMI 30.0 ± 5.2kg/m 2 ) were analyzed to compare the detection of apneas by 2 different methods of combined airflow signals: a) Therm/NP and b) TS/NP. The two scoring methods were performed randomly and independently form each other. Results of respiratory event detection and AHI using Therm/NP signals as a reference were compared to those obtained by TS/NP signals. Results: The number of respiratory events scored using Therm/NP was 7268 while it was 7329 with TS/NP. The average AHI for all patients were 29.8 ± 22.9 for Therm/NP and 30.0 ± 22.6 /hour for TS/NP.  However, 55.3 % of total events scored by Therm/NP were hypopneas while 59.3 % of events scored by TS/NP were apneas. Conclusions: These results show that the association TS/NP reliably detects the same number of respiratory events as Therm/NP despite the difference of apnea to hypopnea ratio between the two methods. The use of TS does not modify AHI calculations and it guarantees accurate sleep apnea diagnosis. Thus, TS can be used as a substitute for oronasal thermistors in sleep recording systems.