Objectives: 

It is generally accepted that some disorders of pulmonary ventilation belong to the group of the proarrhythmogenic factors. Surprisingly, there are only few works describing day-time of the experiment running or synchronization of animals to the light-dark (LD) cycle. It can be a problem, because the LD cycle is given for one of the strongest circadian synchronizators of the animal endogenous rhythms.

Materials: 

The circadian fluctuation of the electrical stability of the heart, measured by ventricular arrhythmia threshold (VAT), was followed during artificial normal ventilation (VT = 1 ml/100g; respiratory rate 50 breath/min), hypoventilation (VT = 0.5 ml/100g; respiratory rate 20 breath/min) and hyperventilation (VT = 2 ml/100g; respiratory rate 70 breath/min) in pentobarbital anesthetized rats (40 mg/kg, ip; the open chest experiments) after adaptation to a daily light-dark cycle of 12h:12h for 4 weeks.

Results: 

The 24h course of the VAT showed the highest susceptibility of the rat ventricular myocardium to arrhythmias between 12:00h and 15:00h and highest resistance between 24:00h and 03:00h under normooxic conditions. Acrophase with confidence intervals were on -3380 (-2880; -70), in time at 22:53h (19:20; 00:28h) with mesor 2,59 ± 0,53 mA and amplitude 0,33 ± 0,11 mA. Hypoventilation decreased the mesor (1,33 mA) and amplitude (0,14 mA). The VAT circadian rhythm was changed to biphasic with smaller peak between 15:00h and 18:00 and higher peak between 24:00 and 03:00h. The hypoventilatory circadian rhythm of the VAT was not significant. The hyperventilatory 24h rhythm of the VAT was non-significant and character, seen during normoventilation, was not changed. Acrophase was shifted to –400 (02:40h), mesor was increased (2,91 mA) and amplitude was decreased (0,13 mA).

Conclusions: 

Disorders of pulmonary ventilation change or modify the circadian rhythm of the electrical stability of the rat heart.