Original scientific paper

https://doi.org/10.17559/TV-20260318003463

Session-Based Salivary pH Assessment for Noninvasive Evaluation of Fatigue-Related Physiological Change During Simulated Driving Under Controlled Oxygen Conditions: A Pilot Feasibility Study

Pil Kee Min ; Department of Informatics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
Kazuyuki Mito ; Department of Informatics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan *

* Corresponding author.

Abstract

Driver fatigue is an important contributor to transportation accidents, but many fatigue assessment methods rely on intrusive physiological sensors or unstable behavioral indicators. This pilot feasibility study evaluated a session-based salivary pH assessment approach for the noninvasive evaluation of fatigue-related physiological changes during simulated driving under controlled oxygen conditions. The study did not test continuous in-drive salivary sensing, a real-time biomarker, or a fully wearable driver monitoring implementation. Fifteen healthy young adult male volunteers initially participated in repeated simulated driving sessions under ambient air (21% oxygen), moderate nominal oxygen exposure (30% oxygen), and high nominal oxygen exposure (40% oxygen). Because four datasets were affected by pH measurement device malfunction and unusable pH records, the final statistical analysis was conducted using complete valid data from 11 participants. Salivary pH was measured before and after each driving session, and within-subject changes were compared across oxygen conditions. Mean salivary pH decreased after simulated driving under all experimental conditions. The mean Delta pH values were ‒0.238 ± 0.551 for 21% oxygen, ‒0.198 ± 0.499 for 30% oxygen, and ‒0.198 ± 0.482 for 40% oxygen. Repeated-measures ANOVA did not identify a statistically significant difference in Delta pH among the three oxygen conditions, F(2, 20) = 0.020, p = 0.980, partial eta squared = 0.002. Therefore, the observed pH decrease should be interpreted as a general pre-to-post driving physiological change rather than evidence of oxygen-specific fatigue mitigation. These findings support only the preliminary feasibility of session-based salivary pH assessment. Larger studies with diverse participants, prospective ethics review or exemption, verified oxygen delivery, stronger salivary-confounder control, quantitative sensor validation, improved device reliability, and comparison with independent physiological, subjective, and behavioral fatigue measures are needed.

Keywords

driver fatigue; noninvasive measurement; oxygen exposure; pilot feasibility study; salivary pH assessment; session-based assessment; simulated driving; transportation safety

Hrčak ID:

353100

URI

https://hrcak.srce.hr/353100

Publication date:

7.11.2026.

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