Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA018

Poster Communications

Arousal from hibernation: patterns of heart rate variability in golden hamsters.

O. V. Shylo1, V. V. Lomako1, G. O. Babijchuk1

1. Cryophysiology, Institute for Problems of Cryobiology and Cryomedicine of the National Academy of Sciences of Ukraine, Kharkiv, Ukraine.

Hibernation-like strategies are considered promising for medical practice and space exploration. Heart rate (HR), an indicator of functional state of the body, greatly fluctuates with cardiac arrhythmias presence throughout hibernation bout. The significance of arrhythmias is still unknown and less studied especially upon arousal from hibernation, the very stage when the blood flow renormalizes in reperfusion-like manner. To clarify the peculiarities of HR dynamics upon arousal from hibernation, male golden hamsters (85-95 g, n=10) towards to the hibernation bout end (average bout duration was 3±0.5 days) were transferred into a warm illuminated room (21±2°C) and sterile needle electrodes for ECG recording (placed under the paws skin), piezoelectric sensors for breathing pattern evaluation (placed at the both side between the animal's body and nest walls) and a thermocouple (placed in the cheek pouch) for body temperature (Tb) measurement were attached. Heart and respiratory signals were recorded and preprocessed with computer-based electrocardiograph Poly-Spectrum (Neurosoft) and then RR intervals data were imported into Kubios 2.2 software (Kubios Oy) to calculate time, frequency and non-linear heart rate variability measures. The recording processes were terminated at Tb=23.5±5.1°C. Data were means±SD, compared by ANOVA. Two different patterns of RR dynamics were found. The first one was characterized by smooth progressive shortenings in mean RR distance (increase in HR) (1785.48±794.85, 921.43±409.31 and 301.73 ±56.88 ms, n=11) and low standard deviation of RR intervals (STD RR) (14.75±15.72, 8.46±6.04, 3.75±1.42 ms, n=11) at the start, middle and end stages of arousal from hibernation respectively. The second one was characterized by period (1364.3±655.6 s, n=17) of regular alternating "long" and "short" RR intervals (bigeminy) appearance and, as the result, by increased STD RR (165.58±63.33, mean RR=852.15±130.28 ms, n=17). The presence of two separate peaks in RR distribution was confirmed by time-domain and non-linear (Poincare plot) analysis. No breathing arrhythmia was revealed at simultaneous ECG and breathing recordings at this stage. Noteworthy, a period characterized by switching HR back to lower level along with total or partial ceasing of arrhythmia wedged into the arrhythmia period. All animals but one kept to a certain type of RR distribution pattern. That one alternated between both patterns in the course of 9 successive bouts. Parasympathetic activation re/appearance was revealed by spectral analysis of heart rate variability only after abrupt arrhythmia termination. Arrhythmia-free and arrhythmia dynamics are possible upon hamsters' arousal from hibernation. The same animal may "produce" both patterns. Arrhythmia episode and switching back into lower HR during that episode are probably to slowing HR and/or metabolic rate increased upon arousal.

Where applicable, experiments conform with Society ethical requirements