Objective: Respiratory alkalosis is an extremely common and complicated problem affecting virtually every organ system of which the etiology may be associated with pulmonary or cardiovascular disorders. However, few studies have addressed the day/night rhythm of the effect of hyperventilation on the cardiovascular system. As such, the aim of the present study was to characterize the circadian rhythm of the electrical stability of the rat heart under hyperventilatory conditions.
Methods: Circadian rhythms of the electrical stability of the
heart, measured according to ventricular arrhythmia threshold (VAT), were
followed during normal artificial ventilation in a control group (respiratory
rate, 40 breaths/min; tidal volume, 1 mL/100g [n=17]) and during hyperventilation
(respiratory rate, 80 breaths/min; tidal volume 2 mL/100 g [n=7]) in female
Wistar rats anesthetized with pentobarbital (40 mg/kg, administered
intraperitoneally), after 4 weeks’ adaptation to a light (12 h)/dark (12 h)
regimen (40%–60% humidity, temperature 24°C, 2 animals per cage with ad libitum
access to food and water), with the dark period from 18:00 h to 06:00 h.
Results are expressed as mean ± standard deviation. The basic circadian
parameters were assessed using single and population mean cosinor tests.
Results: Under normoxic conditions, the 24 h course of VAT
exhibited the highest susceptibility of the rat ventricular myocardium to
arrhythmias between 12:00 h and 15:00 h, and the highest resistance between
19:20 h and 00:28 h (acrophase, -338° [in time at 22:53 h], with confidence
intervals from -288° to -7° [19:20 h to 00:28 h]). The mean mesor (± SD) and
amplitude were 2.59 ± 0.53 mA and
0.33 ± 0.11 mA, respectively. Nonsignificant hyperventilation increased
the VAT at each interval of the measurement but did not alter the
characteristics of circadian rhythm. Acrophase was on -40° (02:40 h), mesor was
increased (2.91 mA), and amplitude was decreased (0.13 mA).
Conclusion: Although hyperventilation insignificantly increased the
electrical stability of the heart compared with values during normal pulmonary
ventilation during the entire 24-hour period, results demonstrated that
hyperventilation probably only modulated―but did not disturb―the circadian
rhythm of the electrical stability of the heart in pentobarbital-anaesthetized
female Wistar rats. These results affirm that light/dark cycle-related
differences are not merely transient or procedure dependent, but are a
systematic response caused by distinct neurohumoral regulation during the light
and dark periods of the day, and also occur under pentobarbital anesthesia.
Author
(s) Details
Pavol Svorc
Department of Physiology, Medical Faculty, Safarik University, Kosice,
Slovak Republic.
Alexander Marossy
Department of Physiology, Medical Faculty, Safarik University, Kosice,
Slovak Republic.
Pavol Svorc Jr
Department of Physiology, Medical Faculty, Ostrava University, Ostrava,
Czech Republic.
Viktoria
Kapsdorferova
Department of Physiology, Medical Faculty, Safarik University, Kosice,
Slovak Republic.
Please see the book here:- https://doi.org/10.9734/bpi/crpbs/v5/2914
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