Split-Night Versus Full-Night Polysomnography: Comparison of the First and Second Parts of the Night

In a split-night study, the first part consists of standard polysomnography (PSG) for the diagnosis of obstructive sleep apnea syndrome while the second part is used to establish a suitable level of continuous positive airway pressure. The aim of our study was to compare the sleep and respiratory parameters during the first 3 hours of the night with the values found during the remainder of sleep and during the whole night. Forty-five patients were included in the study. Each patient underwent a standard full-night PSG and the PSG data for each patient was divided into 2 periods: PSG 1, defined as the initial 3 hours of the total sleep time and PSG 2, defined as the remaining period. Sleep and breathing data from PSG 1 and PSG 2 were then separately computed and compared with each other and with data for the total sleep time (PSGt). The percentage of total sleep time in stage III-IV and the apnea-hypopnea index (AHI) were significantly higher and the percentage of time in rapid eye movement (REM) sleep was significantly lower during PSG 1 than during PSG 2 ( P