A comparative evaluation of accuracy and response time in ear and finger pulse oximetry during repeated maximal...

Pulse oximetry is widely used to monitor training intensity and define safety termination thresholds during breath-hold-related activities, yet its accuracy and response time vary by measurement site, reflecting inherent physiological differences between locations, such as perfusion and vascular tone. Because these physiological variables are markedly altered during breath-holding, this study investigated differences in pulse oximetry dynamics between central (ear) and peripheral (finger) sites during repeated maximal breath-holding.

Forty healthy subjects performed three repeated maximal static breath-holds separated by 2-min rest intervals. Finger and earlobe SpO₂, systemic cardiovascular variables, and gas exchange were assessed.

Breath-holds were terminated at progressively lower end-tidal oxygen and SpO₂, and higher end-tidal carbon dioxide, arterial pressures, and cardiac output across successive attempts (p ≤ 0.003). SpO₂ values at both the breaking point and nadir were consistently higher at the finger than at the earlobe (breaking point: +9-15%; nadir: +7-11%;p ≤ 0.008), with the inter-site differences being amplified across successive attempts (p ≤ 0.012). Finger SpO₂ remained significantly higher at breaking point than at the nadir (+4-8%;p < 0.001), whereas no such differences were noted at the ear (p = 0.619). The time to reach SpO₂ nadir was longer at the finger than at the earlobe (18-23 s;p < 0.001) and was extended across attempts only at the finger (from 27 s to 32 s;p < 0.001). Breath-hold duration correlated with the inter-site SpO₂ differences at breakpoint (r = 0.53;p < 0.001).

Compared to earlobe measurement, finger pulse oximetry exhibited a consistent temporal delay, and systematically underestimated the severity of hypoxaemia. This divergence increased with longer breath-holds, indicating a duration-dependent amplification of the inter-site SpO₂-measurement differences.