Changes in heart rate associated with high-pressure convulsions in rodents

Area of Science:

• Cardiovascular physiology
• High-pressure physiology
• Neuroscience

Background:

• Understanding the physiological effects of heliox atmospheres under compression is crucial for deep-sea exploration and diving.
• High-pressure neurological syndrome (HPNS) is a concern for divers exposed to extreme pressures.
• Previous research indicates varied responses to pressure across species and age groups.

Purpose of the Study:

• To investigate the impact of heliox compression on heart rate in mice and rats of different ages.
• To characterize the cardiac response during high-pressure neurological syndrome (HPNS) seizures.
• To explore potential interventions for mitigating pressure-induced physiological changes.

Main Methods:

• Mice (14 days to adult) and rats (6-8 days, 29 days, adult) were exposed to heliox atmospheres under varying pressures.
• Heart rate was monitored continuously.
• Seizure activity (Type I and Type II HPNS) was observed, and atropine was used as a pretreatment in some experiments.

Main Results:

• In young mice and rats, heart rate generally decreased with pressure, similar to liquid-breathing mice.
• Adult rats showed less bradycardia compared to younger animals.
• Type II (tonic) HPNS seizures were consistently linked to profound, transient bradycardia, which could be blocked by atropine; Type I (clonic) seizures had no significant effect on heart rate.

Conclusions:

• Age and species significantly influence cardiovascular responses to heliox compression.
• Tonic HPNS seizures induce a significant, reversible bradycardia mediated by a pathway sensitive to atropine.
• These findings contribute to understanding HPNS pathophysiology, seizure mechanisms, and high-pressure mortality.