Muscle metaboreflex control of ventricular contractility during dynamic exercise

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Skeletal Muscle Metabolism

Background:

• The muscle metaboreflex (MMR) is a neural reflex activated when oxygen delivery to active skeletal muscles fails to meet metabolic demands.
• MMR elicits increases in heart rate, cardiac output (CO), and arterial pressure.
• The contribution of ventricular contractility to MMR-induced increases in CO remains incompletely understood.

Purpose of the Study:

• To investigate whether MMR activation leads to an increase in maximal left ventricular elastance (Emax), a direct index of ventricular contractility.
• To quantify the extent of contractility changes during MMR activation in conscious animals during exercise.

Main Methods:

• Experiments were conducted on conscious dogs with chronic instrumentation for measuring left ventricular pressure and volume.
• MMR responses were elicited during mild and moderate treadmill exercise by inducing partial hindlimb ischemia.
• Maximal left ventricular elastance (Emax) was calculated as an index of contractility.

Main Results:

• MMR activation significantly increased cardiac output, heart rate, and arterial pressure at both exercise intensities.
• Maximal rate of change of left ventricular pressure also increased with MMR activation.
• MMR activation elevated Emax to approximately 160% of the baseline exercise value, indicating a substantial increase in ventricular contractility.

Conclusions:

• The muscle metaboreflex significantly enhances ventricular contractility during dynamic exercise.
• Increased ventricular elastance is a key mechanism contributing to the rise in cardiac output during MMR activation.
• These findings highlight the integrated cardiovascular response to skeletal muscle metabolic stress.