Ultra-weak photon emission during ischemia-reperfusion: Characterizing response dynamics and reproducibility

Ultra-weak Photon Emission (UPE) is thought to represent chemiluminescence from oxidative metabolic processes. This study aimed to characterize UPE dynamics during transient ischemia and reperfusion, while systematically assessing the reproducibility of both baseline and intervention-induced UPE measurements.

UPE was recorded from the hands of 30 participants across two separate sessions using a custom-built photon-counting system. Transient ischemia was induced by a two-minute upper-arm tourniquet application. The stability and reproducibility of these measurements were evaluated using Bland-Altman analysis, Pearson correlations, and within-subject Coefficient of Variation (wsCV).

UPE intensity exhibited a distinct multiphasic response to blood flow restriction: A sharp decline during ischemia (reaching ∼85% of baseline) followed by stabilization during reperfusion at approximately 95% of baseline. Baseline measurements exhibited high intrasession reproducibility (r = 0.97, wsCV = 11.3%) but only moderate intersession reproducibility (r = 0.59, wsCV = 34.4%). During the intervention, reproducibility was moderate in the ischemic phase (r = 0.66, wsCV = 43.6%), whereas the reperfusion phase showed substantially greater variability (r = 0.32, wsCV = 99.9%). In contrast, normalized AUC quantification produced stronger intersession linear associations and improved reproducibility across both the baseline-ischemia (r = 0.83, wsCV = 28.3%) and reperfusion segments (r = 0.80, wsCV = 35.1%).

UPE is able to capture a dynamic physiological response to blood flow restriction that follows a consistent temporal trend despite significant individual variability. This study establishes quantitative benchmarks for UPE measurement stability, positioning it for future consideration as a non-invasive tool for monitoring oxidative metabolic activity in vivo.