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

Molecular hydrogen (H₂) is produced by human colon microbiomes and exhaled. End-tidal H₂ sampling is a simple method of measuring alveolar H₂. The logarithm of the hydrogen ion (H⁺)/H₂ ratio suggests the electrode potential in the solution according to the Nernst equation. As pH is defined as the negative logarithm of the H⁺ concentration, pH₂ is defined as the negative logarithm of the H₂ effective pressure in this study. We investigated whether changes in pH₂ indicated the variation of electrode potential in the solution and whether changes in end-tidal pH₂ could be measured using a portable breath H₂ sensor. Changes in the electrode potential were proportional to ([Formula: see text]) in phosphate-buffered solution (pH = 7.1). End-tidal H₂ was measured in the morning (baseline) and at noon (after daily activities) in 149 healthy Japanese subjects using a handheld H₂ sensor. The median pH₂ at the baseline was 4.89, and it increased by 0.15 after daily activities. The variation of electrode potential was obtained by multiplying the pH₂ difference, which suggested approximately + 4.6 mV oxidation after daily activities. These data suggested that changes in end-tidal pH₂ indicate the variation of electrode potential during daily activities in healthy human subjects.