Physiol. Res. 49: 711-719, 2000

Relation of Ventricular Fibrillation Threshold to Heart Rate during Normal Ventilation and Hypoventilation in Female Wistar Rats: A Chronophysiological Study


Department of Physiology, Medical Faculty, Šafárik University and 1Technical University, Košice, Slovak Republic

Received September 16, 1999
Accepted March 6, 2000

The aim of our study was to verify the relationship between heart rate (HR) and ventricular fibrillation threshold (VFT) during different types of ventilation in female Wistar rats from the circadian point of view. The ex-periments were performed under pentobarbital anesthesia (40 mg/kg i.p., adaptation to a light-dark cycle 12:12 h, open chest experiments) and the obtained results were averaged independently of the seasons. The VFT measure-ments were performed during normal ventilation (17 animals) and hypoventilation (10 animals). The HR was re-corded immediately before the rise of ventricular arrhy-thmias. Results are expressed as arithmetic means ± S.D. and differences are considered significant when p<0.05. The basic pe-riodic characteristics were calculated using single and population mean cosinor tests. The results from our experiments have demonstrate that 1) the VFT and HR respond identically to hypoventilation by a decrease in the light and also in the dark phases, and 2) hypoventilation changes the 24-h course of the VFT without a change in the 24-h rhythm of the HR. It is concluded that the HR and VFT behave as two independent functional systems without apparent significant circadian dependence during both types of ventilation.

Key words
Rat · Circadian · Ventricular fibrillation threshold · Heart rate · Hypoventi-la-tion

Reprint requests
P. Švorc, Department of Physiology, Medical Faculty, Šafárik University, Tr. SNP 1, 040 66 Košice, Slovak Republic.

© 2000 by the Institute of Physiology, Czech Academy of Sciences