Objective: 

The control of the acid-base balance in the animal experiments with artificial ventilation would be primary effort in all in vivo studies. Problem is that acid-base balance changes after each ventilatory change and results are often comparised to averaged reference values irrespective of the circadian dependence. The aim of study was refered to chronobiological aspects the impact of the artificial ventilation on the pH and blood gases in rat experiments in vivo.

Methods: 

The experiments were performed in ketamine/xylazine anaesthetized female Wistar rats (ketamine 100 mg/kg + xylazine 15 mg/kg, i.m., 3–4 months, open chest experiments) after 4 weeks of adaptation to the LD cycle (12h:12h). The parameters of the initial ventilation and reoxygenation: respiratory rate 50 breaths/min., tidal volume 1ml/100g. Apnoic episode was simulated by the switching off the ventilator for 2 minutes. The acid-base balance was monitored from blood samples taken from the femoral artery.

Results: 

Anaesthesia produced the systemic asphyxia in spontaneously breathing rats independently on LD cycle. LD differences were abolished after the apnoae, except pCO2 with significantly higher values in the light period. 20 min. of reoxygenation evoked acidosis, normocapnia and hypoxia in the light period and alkalosis, hypocapnia and hypoxia in the dark one. LD differences were preserved in all followed parameters.

Conclusions: 

It is concluded that the spontaneously breathing rats under the ketamine/xylazine anaesthesia are in asphyxic conditions from the start of in vivo experiments, independently on LD cycle. The recovery of pulmonary ventilation after apnoae does not rectify pH and blood gases to the reference values and changes them in the dependence on LD cycle.