U-shaped patterns are acceleration-deceleration periods in RR interval series. These
relatively short time events (average duration 29.8 +/- 4.1 s) are the most laminar
structures in the night-time recordings. The aim of this study is a analysis of sleep
events occurring during U-shaped patterns in polysomnography (PSG) recordings obtained
from Sleep Heart Health Study database. 500 PSG recordings were analyzed. U-shaped
patterns were detected and categorized based on sleep stages, body position, respiratory
events and EEG arousals. 4202 U-shaped patterns were found in 463 recordings. The
majority of U-shaped patterns coincide with EEG arousals (73.9%). 48% of the patterns
occurred at sleep phase changes. Most of the U-shaped patterns were associated with
the Wake phase (61%). U-shaped patterns occurred at the position changes in 22.6%
of cases. Analysis of respiratory events showed that U-shaped patterns occurred during
hypopnea in 32.3% of the cases, CSA - 1.7%, OSA - 0.8% and desaturation - 18.6%. The
quantitative analysis of PSG recordings is a first step to discover the origin of
the phenomenon of U-shaped patterns. These first observations show that the U-shaped
patterns are strongly associated with EEG arousals and may play role in sleep regulation.
