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

Abstract

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.

Figure 1

Changes in oxidation–reduction potential (ORP) in phosphate-buffered solution after bubbling air containing 10 Pa of H₂ (pH₂ = 4.0, n = 3) and the atmosphere (pH₂ = 6.22, n = 3) (P = 0.011). ${\text{pH}}_2=-\text{log}\left(\frac{{\text{P}}_{\text{H}2}}{{\text{P}}^0}\right)$, $P^0=1\text{bar}={10}^5\text{Pa}$.

Figure 2

Breath hydrogen (H₂) partial-pressure measurements at baseline and after daily activities. Breath H₂ is end-tidal H₂ partial-pressure (Pa). The median end-tidal H₂ value of breath after daily activities was lower than the median value recorded at baseline (P = 0.007).

Figure 3

Values of pH₂ at baseline and after daily activities. The median value of pH₂ after daily activities was higher than that recorded at baseline (P = 0.038).

Figure 4

Values of pH₂ at baseline and after daily activities in the subjects with/without breakfast. The median value of pH₂ after daily activities was higher than that recorded at baseline in the subjects who had eaten breakfast * (P = 0.001). The closed circle [●] indicates the subjects who had eaten breakfast and the open circle [○] indicates the subjects who had not eaten breakfast.