Passive Hindlimb Cycling Enhances Tolerance of Cardiac Electrical Conduction in Rats with Spinal Cord Injuries

Area of Science:

• Neuroscience
• Cardiology
• Exercise Physiology

Background:

• High-level spinal cord injury (SCI) disrupts autonomic nervous system control of the heart, increasing arrhythmia risk.
• Passive hindlimb cycling (PHLC) is known to maintain cardiovascular function after SCI, but its effect on cardiac electrical disorders is unclear.

Purpose of the Study:

• To investigate the impact of long-term PHLC on cardiac arrhythmias and autonomic function following high-thoracic SCI in rats.
• To determine if exercise training can mitigate SCI-induced cardiac electrical instability.

Main Methods:

• Rats with complete high-thoracic SCI underwent 5 or 10 weeks of PHLC, with control groups including naive rats and SCI-only rats.
• Telemetric recording of blood pressure and electrocardiogram was performed.
• Autonomic dysreflexia was triggered via colorectal distension and cardiac sympathetic activity was stimulated with dobutamine.

Main Results:

• PHLC did not affect SCI-induced hypotension but reduced spontaneous autonomic dysreflexia events.
• 10-week PHLC significantly decreased severe arrhythmias during triggered autonomic dysreflexia and dobutamine stress tests compared to SCI controls.
• Exercise training appeared to reduce the unopposed parasympathetic tone observed post-SCI.

Conclusions:

• Long-term activity-based training, specifically PHLC, improves autonomic balance in SCI rats.
• PHLC enhances the heart's tolerance to electrical conduction disturbances following spinal cord injury.