- Arousal from sleep is a normal physiologic event during normal sleep, which produces a tachycardia-bradycardia pattern on the heart rate variability (HRV) signal, which testifies the involvement of the autonomic nervous system related to a central nervous system event. Repetitive arousals may be associated to excessive sleep fragmentation (for example in respiratory pathologies such as Obstructive Sleep Apnea) and to a bad quality of sleep. In this work we studied the HRV signal in the time-frequency domain during isolated and repetitive arousals. During isolated arousal episode, time and frequency domain parameters showed the behavior associated to vagal withdraw and sympathetic activation. Multivariate time-variant AR model was used to evaluate interaction between HRV and respiration during repetitive arousals. We found an increased synchronization between HRV and respiration and an entrainment between LF oscillation and respiration at the frequency of micro-arousals.