Does inadequate oxygen delivery trigger pressor response to muscle hypoperfusion during exercise?

Area of Science:

• Exercise Physiology
• Cardiovascular Regulation
• Skeletal Muscle Metabolism

Background:

• Exercise elicits pressor responses, increasing systemic arterial pressure (SAP).
• The underlying mechanisms, particularly the role of oxygen delivery and metabolic byproducts, require further elucidation.

Purpose of the Study:

• To investigate the hypothesis that inadequate oxygen delivery during exercise leads to the accumulation of a muscle-derived "pressor substance" that activates nerves.
• To determine if this pressor substance release is correlated with changes in femoral venous blood composition and SAP.

Main Methods:

• Dogs exercised on a treadmill at varying speeds and inclines.
• Systemic arterial pressure (SAP) and hindlimb perfusion were monitored.
• Arterial oxygen content (CaO2) was reduced using carbon monoxide (CO) inhalation during exercise.
• Femoral venous blood was analyzed for potassium ([K+]), pH, and lactate concentrations.

Main Results:

• Graded reductions in hindlimb perfusion reflexly elicited pressor responses.
• CO inhalation reduced CaO2, shifting the relationship between SAP and exercise intensity.
• SAP changes were well correlated with pH and lactate levels, but not potassium, suggesting a metabolic link.
• Pressor responses were linked to a critical threshold of oxygen delivery, leading to the accumulation of a pressor substance.

Conclusions:

• Pressor responses during exercise are initiated when oxygen delivery falls below a critical level.
• This triggers the accumulation of a pressor substance, linked to metabolic events and lactate accumulation.
• Potassium is not a primary signal for the pressor response in this context.