Changes in the negative logarithm of end-tidal hydrogen partial pressure indicate the variation of electrode potential in healthy Japanese subjects.

Abstract

Molecular hydrogen produced by colonic microbiota is exhaled and can be sampled non-invasively as end-tidal H₂. Applying the Nernst equation, the H⁺/H₂ ratio logarithm reflects electrode potential in solution; by analogy with pH, the authors defined pH₂ as the negative logarithm of H₂ effective pressure. In phosphate-buffered solution (pH 7.1), electrode potential changes were proportional to pH₂ differences. A handheld H₂ sensor was used to measure end-tidal H₂ in 149 healthy Japanese participants at two time points: morning baseline and noon after routine daily activities. The median baseline pH₂ was 4.89, rising by 0.15 units at noon. Multiplying this difference by the relevant Nernst coefficient indicated an oxidation shift of approximately +4.6 mV following daily activities. The findings suggest that end-tidal pH₂ monitoring can serve as a practical, portable means of tracking redox electrode potential fluctuations in healthy individuals.

Mechanism

Based on the Nernst equation, the logarithm of the H⁺/H₂ ratio is proportional to electrode potential in solution; therefore, pH₂ (negative logarithm of end-tidal H₂ partial pressure) serves as a proxy for in vivo redox potential shifts.