Photoplethysmography-Derived Flow-Mediated Dilation as a Non-Invasive Marker of Endothelial Function in Erectile Dysfunction

Figures

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  Figure 1. Overview of the PPG-FMD measurement and analysis workflow. (A) PPG signals were recorded from the index finger of each hand (left: active, right: control) using a Biopac MP36 module with two SS4LA sensors and processed in MATLAB. (B) Protocol: 4-min baseline, 5-min cuff occlusion at 200 mmHg, and 4-min reperfusion. (C) Signal processing: correction, normalization, and curve fitting to generate the result curve. (D) Derived parameters: dilation index (DI), time to maximum dilation (Tmax), area under the curve (AUC), and dilation index slope (DIslope). PPG-FMD: photoplethysmography-derived flow-mediated dilation.

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  Figure 2. An illustrative DI over time and an explanatory representation of the calculated outcome parameters on the curve. The zero point on the time axis represents the moment when the occlusion ends and reperfusion begins. PPG-DI: maximum dilation index; DIslope: the slope of the line drawn from the onset of reperfusion to the point of maximum dilation index on the curve; Tmax: the time elapsed from the beginning of reperfusion to reach maximum response: AUC: the area under the curve of the portion of the curve above zero.

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  Figure 3. Endothelial function results of the study groups, including (a) dilation index, (b) Tmax values, (c) AUC values, and (d) DIslope values. Boxes represent the interquartile range (Q1–Q3), the horizontal line within each box indicates the median, and whiskers extend from the minimum to the maximum value. According to ANOVA, differences in the dilation index and AUC values were statistically significant (p < 0.01 for both). Pairwise comparisons are indicated in the figure (* p < 0.01).

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  Figure 4. ED: Erectile dysfunction. Representative PPG-FMD result curves from individual participants: (a) a vascular ED patient, (b) another vascular ED patient, (c) a non-vascular ED patient, and (d) a control participant. The graphs illustrate qualitative differences in vasodilation responses across the groups. ED: erectile dysfunction.

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  Figure 5. ED: Erectile dysfunction. Mean PPG-FMD curves of five randomly selected participants from each study group. The vascular ED (VED) group demonstrates a markedly attenuated and shorter-lasting vasodilation response compared to the non-vascular ED (Non-VED) and control groups. VED: vascular erectile dysfunction; non-VED: non-vascular erectile dysfunction; PPG-FMD: photoplethysmography-derived flow-mediated dilation.