Sixty-minute inhalation of molecular hydrogen decreases blood oxygen saturation but does not alter autonomic cardiac regulation at rest in healthy females: A randomized, double-blind, placebo-controlled crossover study

This randomized, double-blind, placebo-controlled crossover study investigated the effects of 60-minute molecular hydrogen inhalation on oxygen saturation and heart rate variability in healthy females. Twenty physically active participants completed two inhalation sessions with either molecular hydrogen or placebo (ambient air), separated by a seven-day washout period. Oxygen saturation and heart rate variability were monitored during 60 minutes of inhalation. The dataset contains basic anthropological characteristics of participants. The oxygen saturation value represents the average value taken from a 5-minute segment. The heart rate variability values represent the time- and frequency-domain indices calculated from a 5-minute segment.

Methods
Experimental protocol

The research was conducted as a randomized, double-blind, placebo-controlled crossover study. Twenty physically active female sports science students years were divided randomly into two experimental groups. One group inhaled molecular hydrogen and the other group inhaled a placebo for 60 minutes. Following a seven-day washout period, a second experimental session was conducted where molecular hydrogen and placebo inhalation were reversed. Molecular hydrogen (flow of 300 ml/min, purity of 99.8%) was produced by a generator i300 (Molecular Hydrogen Medical Technologies, Ostrava, Czech Republic). Placebo was delivered using a modified generator that pumps ambient air. Participants were seated and a chest strap (Polar Pro Strap, Polar, Kempele, Finland) was placed. A pulse oximeter sensor was placed on right index finger. They were then fitted with a nasal cannula supplying molecular hydrogen or placebo. Subsequently, SpO2 and ECG signal were recorded for 60 minutes in an inactive seated position.

Anthropometric measurement

Body mass and body fat were measured using bioimpedance analysis (Tanita MC-980 MA, Tanita, Tokyo, Japan). Body height was measured using a stadiometer (SOEHNLE 7307, Leifheit, Nassau, Germany).

Oxygen saturation measurement

SpO2 was measured with sampling frequency of 1.0 Hz using a Nonin Avant 2120 pulse oximeter (Nonin Medical, Minneapolis, MN, USA). The 60-minute recording was divided into 12 segments lasting 5 minutes and the average value was calculated for each segment.

Heart rate variability measurement

RR intervals were measured using the DiANS PF8 diagnostic system (DIMEA Group, Olomouc, Czech Republic). The 60-minute recording was divided into 12 segments lasting 5 minutes. Time-domain indices included RMSSD and SDNN. Spectral analysis was based on fast Fourier transform and processed from a set of 300 consecutive artifact-free RR intervals extracted from each 5-minunte segment. Two frequency bands were used: 0.05 to 0.15 Hz for LF, and 0.15 to 0.50 Hz for HF.