Symbolic dynamics of pulse transit time and heart period in children with upper airway obstruction

Upper airway obstruction (UAO) is a relatively common condition during childhood that is characterized by periods of partial or complete upper airway closure, resulting in restless sleep. It has also been suggested that UAO triggers early cardiovascular changes that may predispose to an increased risk of developing cardiovascular diseases later in life. The aim of this study was to assess the temporal dynamics of heart period (HP) and pulse transit time (PTT) during quite, event-free periods of sleep in children with UAO (n = 40) and matched healthy controls. The dynamics of HP and PTT were symbolized based on the sextiles of their distribution and words of length three were formed and classified into four types based on their patterns. Joint symbolic dynamics represent the concomitant occurrence of words in HP and PTT. Children with UAO showed a significantly increased frequency in word types of monotonously increasing and decreasing HP and PTT as well as joint dynamics across all stages of sleep. The dynamics of HP showed a marked sleep stage dependence, while PTT dynamics appeared to be relatively unaffected. In conclusion, cardiovascular dynamics are altered in children with UAO during scored event-free sleep, indicative of frequent bursts in sympathetic nervous system activity, possibly reflecting subcortical arousal responses to brief and subtle increases in UAO.