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

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