Optimizing In Vivo Perfusion Assessment by Laser Doppler Flowmetry-Effects of Probe Geometry and Signal Normalization

Background/Objectives: Laser Doppler flowmetry enables rapid and simple measurement of microcirculation. However, variations in probe configuration can influence signal acquisition, making it essential to understand each probe's characteristics when selecting equipment for specific physiological assessments. Therefore, this study aimed to compare perfusion measurements obtained with single-fiber (VP1T) and multi-fiber (VP1T/7) probes and to evaluate the effects of normalization strategies. Methods: Nine healthy female volunteers were recruited. Probes were positioned on the palmar aspects of the index and middle fingers of both hands while participants underwent a standardized brachial artery occlusion protocol. Data are presented as mean ± standard error of the mean. Correlations were assessed using Pearson's correlation coefficient. Coefficients of variation (CV) and intraclass correlation coefficients were calculated. Baseline normalization was applied to measurements. Statistical analyses were performed using Student's t-test, with significance set at p < 0.05. Results: Analysis of the full protocol revealed significant positive correlations between probes, indicating consistent temporal perfusion patterns. The VP1T/7 probe yielded significantly higher perfusion values than the VP1T probe, although both exhibited similar CVs. Inter-probe reliability was good, and intra-probe reproducibility ranged from good to excellent, particularly for the VP1T/7 probe. During the reperfusion phase, significant differences were observed only for ipsilateral measurements obtained with the VP1T probe. Normalization effectively reduced variability, and significant differences during reperfusion were detected with both probes. Conclusions: Although the multi-fiber probe consistently recorded higher perfusion values, normalization was essential to reduce variability and to enhance the detection of microvascular reactivity parameters.