Objective: 

The aim was to gain information about the effect of the artificial reoxygenation on heart rate variability (HRV) after apneic episode, as function of the light-dark cycle.

Methods: 

The experiments were performed in ketamine/xylazine anaesthetized female Wistar rats (10mg/kg+15mg/kg), after adaptation to the LD cycle of 12:12h. Reoxygenation was simulated by respiratory pump with parameters 1ml/100g and 50 breaths/min. The apnea was induced by the switch off pump for 2min. HRV parameters (RR, VLF, LF, HF and VLF/HF) were evaluated in the intact animal, after 5min of stabilization followed surgical interventions and after 5.,10.,15.,20. minute of reoxygenation after apnea.

Results: 

In the spontaneous breathing ketamine/xylazine anaesthetized rats, the significant LD differences were found in all parameters, except power VLF and VLF/HF ratio. Only 5 minute of the reoxygenation kept significant LD differences in all followed parameters but this dependence was eliminated by long-term reoxygenation. The dominant parasympathetic tone was preserved during whole experiment in the both lighted parts.

Conclusions: 

It is concluded that this type of anaesthesia increases the parasympathetic and decreases sympathetic tone with the preservation of LD differences. Long-term reoxygenation is without effect on the autonomic nervous system drive and eliminates LD differences.