Skeletal muscle chemoreflex and pHi in exercise ventilatory control

Area of Science:

• Exercise Physiology
• Muscle Metabolism
• Respiratory Control

Background:

• The role of skeletal muscle metabolites in regulating breathing during exercise is not fully understood.
• Investigating the contribution of muscle hydrogen ions to ventilatory drive is crucial for understanding exercise physiology.

Purpose of the Study:

• To determine if skeletal muscle hydrogen ion concentration mediates ventilatory drive in humans during exercise.
• To explore the relationship between muscle intracellular pH and minute ventilation.

Main Methods:

• 12 healthy subjects performed isotonic submaximal quadriceps exercise.
• 31P-magnetic resonance spectroscopy (31P-MRS) measured vastus medialis intracellular pH (pHi).
• Positive pressure cuffs were used to accentuate muscle chemoreflex during exercise or recovery.

Main Results:

• Exercise with accentuated chemoreflex (BLPPex) resulted in higher minute ventilation compared to recovery (BLPPrec).
• BLPPex led to lower arterialized PCO2 and more acidic quadriceps pHi.
• Muscle intracellular pH (pHi) showed a linear relationship with minute ventilation, but arterialized pH did not.

Conclusions:

• Skeletal muscle hydrogen ions contribute to the exercise ventilatory response.
• The findings suggest that muscle acidity, rather than arterial pH, is a significant factor in ventilatory control during exercise.