Arterial H+ regulation during exercise in humans

Area of Science:

• Exercise Physiology
• Human Physiology
• Biochemistry

Background:

• Arterial H+ concentration ([H+]a) is tightly regulated at rest, despite high production rates.
• Understanding the precise regulation of [H+]a during exercise is crucial for interpreting physiological responses.

Purpose of the Study:

• To determine the precision of arterial H+ concentration ([H+]a) regulation during progressively increasing exercise workloads.
• To investigate the relationship between [H+]a, PaCO2, and ventilation (V˙(E)) across different exercise intensities.

Main Methods:

• Measurements of [H+]a, PaCO2, and V˙(E) in 16 healthy subjects during incremental exercise.
• Analysis of ventilatory and acid-base responses relative to exercise intensity and the lactic acidosis threshold (LAT).

Main Results:

• Ventilation (V˙(E)) increased with [H+]a, initially driven by PaCO2 below the LAT.
• Above the LAT, [H+]a increased more significantly relative to V˙(E), indicating a shift to metabolic acidosis.
• PaCO2 initially increased with work rate but decreased above the LAT, while [H+]a continued to rise.

Conclusions:

• Arterial H+ concentration ([H+]a) is regulated throughout the full range of exercise.
• The regulation of [H+]a becomes less sensitive above the lactic acidosis threshold (LAT).
• Exercise-induced acidosis transitions from primarily respiratory to metabolic as exercise intensity increases beyond the LAT.