[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 were divided into 2 periods: PSG1, defined as the initial 3 hours of the total sleep time and PSG2, defined as the remaining period. Sleep and breathing data from PSG1 and PSG2 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 PSG1 than during PSG2 (P< .001). Similarly, the percentage of time in stage III-IV sleep was significantly higher and the percentage of REM sleep was significantly lower during PSG1 than during PSGt (P< .001), but there was no significant difference in the AHI between PSG1 and PSGt.

The diagnosis for the first 3 hours of the night will give a reliable reflection of the whole night. In addition, optimal positive airway pressure titrated during the second half of the night is also optimal for the first half of the night.