Screening of Sleep Apnea by Holter Electrocardiography: Validation of Heart Rate Variability Analysis Algorithm

Holter electrocardiogram monitoring will be carried out for 24 h simultaneously with the PSG monitoring using a 2- lead ambulatory electrocardiograph (Fysiologic; kind courtesy: MedTech Company, Amsterdam, Holland). We will calculate the time-domain, frequency-domain and non-linear indices by HRV. Several parameters describing the differences between RR intervals will be calculated: the square root of the mean of the sum of the squares of differences between adjacent normal RR intervals (r-MSSD), SD of NN intervals (SDNN), SD of the averages of NN intervals in all 5-minute segments of the recording (SDANN), and mean of the SD of all NN intervals for all consecutive 5-minute segments of the recording (SDNN index). All variables will be calculated for the 24-hour, daytime (2:00 to 9:00 PM), and nighttime (midnight to 7 AM) periods, and the differences between daytime and nighttime values (D\[D/N\]) will be computed.