Cardiac autonomic blockade in exercising dogs

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology

Background:

• The autonomic nervous system significantly influences cardiac function during physical activity.
• Understanding the specific roles of sympathetic and parasympathetic systems in regulating heart rate and contractility during exercise is crucial.

Purpose of the Study:

• To investigate the effects of complete autonomic blockade on cardiac function in dogs during graded treadmill exercise.
• To elucidate the contributions of autonomic control to heart rate, cardiac output, and myocardial contractility across different exercise intensities.

Main Methods:

• Pharmacological autonomic blockade using atropine (parasympathetic) and propranolol (sympathetic) in conscious dogs.
• Measurement of heart rate, cardiac output, and left ventricular pressure derivatives during rest and treadmill exercise (mild, moderate, severe).

Main Results:

• Cardiac denervation led to increased resting heart rate but decreased heart rate during moderate and severe exercise.
• Cardiac output was unchanged at rest and mild exercise but reduced during moderate and severe exercise.
• Myocardial contractility, assessed by dP/dt, was reduced at rest and during all exercise intensities.

Conclusions:

• Autonomic blockade diminishes cardiac output during exercise primarily by reducing heart rate and myocardial contractility.
• Cardiac autonomic control is essential for maintaining cardiac output during moderate to severe exercise.
• Autonomic influences on cardiac output are intensity-dependent and less critical at rest or during mild exertion.