An LRP as well as a simultaneously supervised PSG were performed in the sleep laboratory with the same HRP equipment. Scoring of LRP and HRP were performed independently by the same investigators, who were blinded to the identity of the recordings. The supervised nocturnal PSG and LRP were performed in the sleep laboratory. For the overnight PSG, the Deltamed Coherence 3NT Polysomnograph, version 3.0 system (Diagniscan S.A.U., Group Werfen) was used and recorded EEG, right and left electrooculogram, tibial and submental (leg and chin) electromyogram, ECG, oronasal flow by thermistor, chest-abdomen movements with bands, body position by a position sensor, oxygen saturation using pulse oximetry (Spo2) (Nellcor Puritan Bennett, NPB-290), snoring and airflow by means of a nasal cannula, and a continuous transcutaneous recording of CO2. The American Academy of Sleep Medicine criteria were used to evaluate sleep states and respiratory events18 in the PSG. Both HRP and LRP were scored manually, with the American Academy of Sleep Medicine criteria being used to evaluate respiratory events. In this study, hypopnea in the RP was defined as a decrease > 50% in the amplitude of the nasal pressure or alternative signal compared with the preevent baseline excursion and the fall in the nasal pressure signal amplitude lasting ≥ 90% of the entire respiratory event compared with the signal amplitude preceding the event, and accompanied by an Spo2 decrease ≥ 3% for at least the duration equivalent to two respiratory cycles. Flow limitation events were defined as a discernible drop in the amplitude of the nasal cannula signal < 50% compared with the baseline level and/or a flattening of the nasal pressure waveform, accompanied by snoring, noisy breathing, or visual evidence of respiratory effort, lasting at least two respiratory cycles. The apnea-hypopnea index was defined as the number of apneas and hypopneas, including central apneas per hour of sleep in the PSG (per recorded hour in the RP). The obstructive apnea-hypopnea index (OAHI) was defined as the number of obstructive apneas and hypopneas per hour of sleep in the PSG (per recorded hour in the RP), without taking into account central apneas. The flow limitation index was defined as the total number of flow limitation events per hour of sleep in the PSG (per recorded hour in the RP). The respiratory disturbance index (RDI) was defined as the number of apneas (including central apneas), hypopneas, respiratory-related arousals, and flow limitations per hour of sleep in the PSG. Since no arousals can be objectively identified during RP, the RDI included only respiratory events per recorded hour. The obstructive respiratory disturbance index (ORDI) was defined as the number of obstructive apneas, hypopneas, and flow limitation events per hour of sleep in the PSG (per recorded hour in the RP), without taking into account central apneas.