Can alveolar pCO2 exceed pulmonary end-capillary CO2? Yes

Area of Science:

• Physiology
• Biophysics

Background:

• Christian Bohr's 1891 observation that alveolar PCO2 can exceed arterial PCO2 under specific conditions.
• This phenomenon, initially attributed to experimental error, suggests potential lung CO2 secretion.
• Recent rediscovery using modern techniques necessitates a re-evaluation of Bohr's hypothesis.

Purpose of the Study:

• To explain the mechanism behind the observed phenomenon of alveolar PCO2 exceeding arterial PCO2.
• To propose a novel hypothesis for CO2 secretion by the lung that does not involve cellular secretion.

Main Methods:

• Review of historical and recent experimental findings.
• Theoretical modeling of diffusion and chemical reaction kinetics near charged surfaces.
• Analysis of the role of capillary wall charge and blood flow in gas transport.

Main Results:

• A physical-chemical explanation involving the coupling of diffusion and chemical reactions (H+, HCO3-, CO2) near a negatively charged capillary wall.
• Elevated PCO2 near the capillary wall compared to the bulk blood phase.
• Alveolar PCO2 reflects the PCO2 near the capillary wall, not the bulk blood.

Conclusions:

• The Charged Membrane Hypothesis provides a non-cellular explanation for the observed CO2 secretion phenomenon.
• The phenomenon is attributed to a physical-chemical disequilibrium within pulmonary capillaries, sustained by blood flow.
• This challenges traditional views of CO2 transport and secretion in the lungs.