Telemetric measurement of rats during experimental dives in a hyperbaric chamber – a pilot study

Overview

SCUBA diving is associated with significant changes in human physiology. The most influenced organ systems are the cardiovascular, respiratory and nervous system. Traditionally, the diver is monitored pre and post dive, since environmental conditions while diving represents the main technological constraints for real-time measurements. These, together with the complexity of triggered physiological changes, limit our deep understanding of the effect of scuba diving on a diver’s physiology. The aim of this study was to develop and test telemetric measurement of heart rate and heart rate variability (HRV) in un-anesthetized conscious rats during experimental dives in the experimental hyperbaric chamber. Our pilot study showed the feasibility of telemetric measurement of heart rate and HRV up to pabs 300 kPa. Data indicate, that oxygen sensing might play a more significant role in cardiovascular adjustment to hyperbaric hyperoxia, however, more experiments are needed to fully understand underlying mechanisms.

Keywords:

heart rate – diving – rat – hyperoxia – telemetry

INTRODUCTION

Hyperoxic hyperbaric exposure has significant effects on the cardiovascular system, including bradycardia, hypertension, vasoconstriction, reduced cardiac output, and endothelial dysfunction. The baroreflex-mediated pathway is believed to be the underlying mechanism. Although these effects have been investigated for many years, and several hypotheses have been proposed to explain them individually, no physiological process that links them through a common mechanism is known [1]. In addition, to better understand underlying mechanisms determining hyperoxic bradycardia, an animal model was developed and cardiovascular changes associated with normobaric and hyperbaric hyperoxia were investigated in a telemetry monitored conscious rats.

MATERIAL AND METHODS

Six male Wistar rats prenatally exposed to a low oxygen environment (H), consisting of 10.5% O₂ in 89 % N₂ for 4 hours per day during final days (day 19 and 20) of gestation [2] and 5 control (C) Wistar rats were kept on a 12:12-hour light/dark cycle. Animals were implanted with a fluid-filled tip sensor (PA-C40; Data Sciences Int., Minnesota, USA) allowing radio-telemetric measurement of heart rate (HR) with a high frequency (up to 2000 Hz). From this data, we can evaluate heart rate variability (HRV; LF, HF, LF/HF) and spontaneous baroreflex sensitivity (sBRS). After the full post-surgery recovery, rats were enabled to habituate to the experimental conditions in the experimental hyperbaric chamber (3 shame exposures, 1x daily, same daytime). In the consecutive days, animals were placed in the experimental hyperbaric chamber, recorded for 10 min and exposed for 30 minutes to mild hyperbaric hyperoxia while breathing air at 20 m (ppO₂ 63 kPa, p_abs 300 kPa) or normobaric hyperoxia while breathing EAN67 (ppO₂ 67 kPa, p_abs 100 kPa). HR, HRV, and sBRS were calculated. The experiments were proved by the Ethical committee of the Institute of Experimental Pharmacology and Toxicology, Slovak Academy of Sciences and the by the State Veterinary and Food Authority of the Slovak Republic.

RESULTS

Rats restrained in dark, soundproof and scentless hyperbaric chamber showed no significant effects of habituation in HR (p = 0.55), LF/HF (p = 0.17) and sBRS (p = 0.66) in both groups during shame dives (normobaric normoxia). In addition, no significant differences in HR (p = 0.98) and LF/HF (p = 0.55), between C and H group was observed in this experimental setup, while sBRS was significantly (p < 0.05) decreased in H in comparison to C rats.

Hyperbaric and normobaric hyperoxic exposure led to the development of significant hyperoxic bradycardia (p ≤ 0.001). Changes in the HR were not accompanied by significant changes in HRV, nor body core temperature and locomotor activity. However, sBRS showed a tendency for a modulated response when H rats were exposed to normobaric and hyperbaric hyperoxia (Fig. 1).

Figure 1. Mean heart rate, heart rate variability (LF, HF) and spontaneous baroreflex sensitivity during various exposures in H rats (ANOVA, Tukey posthoc test)

This study showed the feasibility of telemetric measurement of HR and HRV up to pabs 300 kPa. Data indicate, that oxygen sensing might play a more significant role in cardiovascular adjustment to hyperbaric hyperoxia, however, more experiments are needed to fully understand underlying mechanisms.

Acknowledgment

The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FRP/2007-2013/ under REA grant agreement n° 264816 and by grants VEGA 1/0686/12, 2/0107/12 and NOREG.

Do redakce došlo dne 5. 9. 2018.

Do tisku přijato dne 11. 9. 2018.

Adresa pro korespondenci:

Dr. Miroslav Rozložník

Department of Biomedical Sciences, Medical Faculty in Ostrava

Czech Republic

e-mail: miroslav.rozloznik@osu.cz