Cardiovascular and respiratory reflexes from muscles during dynamic and static exercise

Area of Science:

• Physiology
• Neuroscience

Background:

• Muscle contractions can elicit reflex responses.
• The origin and nature of these reflexes are not fully understood.

Purpose of the Study:

• To investigate the reflex responses to rhythmic and tetanic hindlimb muscle contractions in rabbits.
• To determine the origin of these reflexes and identify potential receptor sources.

Main Methods:

• Eliciting muscle contractions via femoral nerve stimulation in anesthetized and deafferented rabbits.
• Measuring systemic blood pressure, heart rate, vascular resistance, and pulmonary ventilation.
• Performing nerve sections and curare administration to isolate reflex pathways.

Main Results:

• Rhythmic contractions decreased blood pressure, heart rate, and hindlimb vascular resistance, while increasing respiration.
• Tetanic contractions increased arterial pressure, nonexercising hindlimb vascular resistance, and ventilation.
• Responses were abolished by somatic nerve section or central vagotomy, indicating reflex initiation within the limb.

Conclusions:

• Both depressor and pressor responses are reflexes initiated in contracting muscles.
• Metabolites released from exercising muscles are the likely source of these reflexogenic signals.