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

Molecular hydrogen (H 2 ) is produced by human colon microbiomes and exhaled. End-tidal H 2 sampling is a simple method of measuring alveolar H 2 . The logarithm of the hydrogen ion (H + )/H 2 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, pH 2 is defined as the negative logarithm of the H 2 effective pressure in this study. We investigated whether changes in pH 2 indicated the variation of electrode potential in the solution and whether changes in end-tidal pH 2 could be measured using a portable breath H 2 sensor. Changes in the electrode potential were proportional to ( pH_2-2×pH ) in phosphate-buffered solution (pH = 7.1). End-tidal H 2 was measured in the morning (baseline) and at noon (after daily activities) in 149 healthy Japanese subjects using a handheld H 2 sensor. The median pH 2 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 pH 2 difference, which suggested approximately + 4.6 mV oxidation after daily activities. These data suggested that changes in end-tidal pH 2 indicate the variation of electrode potential during daily activities in healthy human subjects.