U-shaped patterns in HRV from a polysomnographic point of view: a quantitative analysis

Mateusz Soliński1, Jan Żebrowski1, Paweł Kuklik2
1Faculty of Physics, Warsaw University of Technology, 2Department of Cardiology, Asklepios Hospital St. Georg, Hamburg, Germany, Faculty of Medicine, Semmelweis University Campus Hamburg, Hamburg, Germany


U-shaped patterns are acceleration-deceleration periods in RR interval series, observed mostly during sleep. These relatively short time events (average duration 29.8±4.1 s) are the most laminar structures in the night-time recordings. The phenomenon is different from the well-known HRV asymmetry observed by Porta et al. Previous studies showed that these patterns have a considerable impact on the HRV parameters describing the VLF component, persistency, nonlinear correlations and multifractal properties, although their percentage contribution is small compared to the whole night-time series (on the average 3.1±1.7%). The aim of this study is a quantitative analysis of sleep events occurring during U-shaped patterns in polysomnography recordings obtained from Sleep Heart Health Study database. 500 polysomnography recordings were analyzed and included 244 male and 256 female adults (>40 years old). RR interval series were extracted from ECG recordings and the 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 with a mean value of 8.4(7.7) per patient. The majority of U-shaped patterns coincide with EEG arousals (74%). 48% of the patterns occurred at sleep phase changes. Most of the U-shaped patterns were associated with the Wake phase (63%). U-shaped patterns occurred at different body positions: supine – 26.0%, prone – 22.4%, right – 15.2%, left 14.3% and at the position changes – 22.6%. Analysis of respiratory events showed that U-shaped patterns occurred during hypopnea in 33% of the cases, central apnea - 2%, obstructive apnea - 1% and desaturation – 19%. The quantitative analysis of polysomnography 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 occur for different conditions during sleep and could be difficult to explain by a single physiological mechanism.