The exercise pressor reflex and chemoreflex interaction: cardiovascular implications for the exercising human.

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Autonomic Nervous System

Background:

• The exercise pressor reflex (EPR) and chemoreflex (CR) are known sympathoexcitatory mechanisms.
• The combined cardiovascular effects of EPR and CR during exercise are not fully understood.

Purpose of the Study:

• To investigate the interactive cardiovascular consequences of co-activating the EPR and CR during exercise.
• To determine if the interaction differs based on the method of CR activation (hypoxia vs. hypercapnia).

Main Methods:

• Healthy participants performed single-leg knee-extension exercise.
• The EPR was modulated using intrathecal fentanyl to block group III/IV afferent feedback.
• The CR was activated by breathing either ambient air, normocapnic hypoxia, or normoxic hypercapnia.

Main Results:

• Co-activation of EPR and hypoxia-induced CR resulted in hyper-additive increases in blood pressure and heart rate, but hypo-additive reductions in leg blood flow and vascular conductance.
• Co-activation of EPR and hypercapnia-induced CR showed additive interactions for all cardiovascular parameters.
• Hypoxia-induced CR interaction with EPR most significantly impacted peripheral hemodynamics and likely exercise capacity.

Conclusions:

• EPR and CR co-activation lead to significant cardiovascular interactions, with distinct effects depending on CR stimulus.
• The interaction with hypoxia-induced CR, characterized by potentiated blood pressure and restricted peripheral blood flow, has the most substantial functional implications for exercising humans.