[Circadian rhythm of the ventricular fibrillation threshold in a model of hypoventilation-reoxygenation in female Wistar rats].
Hypoxia, similarly as myocardial ischemia, decreases the electric stability of the heart and thus produces the conditions for the genesis of ventricular arrhythmias within the 24 h period however a prompt restoration of oxygen supply or blood flow within myocardium causes serious ventricular arrhythmias. Therefore the aim of our study was to evaluate the reoxygenation impact on myocardium after hypoventilation in circadian dependence. The experiments were performed in female Wistar rats (pentobarbital anesthesia 40 mg/1 kg i.p., open chest experiments). The animals were adapted to the light regimen 12:12 hours, with the dark phase from 18.00 h to 06.00 h. Normal ventilation was used in the control group (n = 17) and in the second one (n = 4), 20 min reoxygenation followed 20 min of hypoventilation. The heart rate (HR) had been recorded just before the ventricular arrhythmias rose. Hypoventilation decreased significantly (p < 0.001) the VFT and HR when compared with the control group and changed the 24-hour rhythm of VFT to moderate bi-phase one. Reoxygenation counter changed this rhythm to inverse in the comparison with the control group. The lowest VFT values occurred when the top of VFT circadian rhythm was detected during normal ventilation. No dependence was detected between VFT and HR in both ventilation types. It is concluded that reoxygenation alternates the myocardial vulnerability to ventricular arrhythmias in dependence on alternation of light and dark and without the evident dependence on HR in the course of the whole 24-hour period. (Tab. 2, Fig. 2, Ref. 43.)
Svorc
P
P
Department of Physiology, School of Medicine, Safarikicnsis University, Kosicc, Slovakia. psvorc@central.medic.upjs.sk
Bracokova
I
I
Podlubny
I
I
Kassayova
K
K
Dorko
E
E
D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D006339:Heart Rate; D007040:Hypoventilation / Q000503:physiopathology*; D010100:Oxygen / Q000008:administration & dosage / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014693:Ventricular Fibrillation / Q000503:physiopathology*
D010100:Oxygen