Enhancing the quantification of post-occlusive reactive hyperemia: a multimodal optical approach

Post-occlusive reactive hyperemia (PORH) is a physiological response marked by a transient increase in microvascular perfusion following ischemia. While cutaneous perfusion during PORH has been extensively characterized using optical approaches such as Doppler-based techniques, low-cost alternatives like photoplethysmography (PPG), videocapillaroscopy (VC) and near-infrared reflectance imaging (NIRI) may provide complementary insights into both microvascular and venous dynamics. However, their role in quantifying PORH remains underexplored. This study aimed to evaluate the potential of low-magnification VC and NIRI-based imaging for quantifying perfusion changes during a standardized PORH protocol in healthy subjects, using PPG as a reference. Fourteen participants (21.5 ± 4.2 years) underwent suprasystolic occlusion of a randomly selected upper limb, with simultaneous recordings using PPG and VC at the finger and NIRI at the dorsal hand veins. The protocol included a 5-min baseline, 3-min occlusion (200 mmHg), and 5-min recovery. Skin blood flow was derived from the PPG signal, a hemoglobin index (C_Hb) was extracted from VC images, and vein width was measured using NIRI. Nonparametric statistics were used for analysis. Arterial occlusion significantly reduced skin blood flow (-95.3%, p < 0.001) and C_Hb (-8.3%, p = 0.007), with milder contralateral changes. Vein width increased during occlusion (p = 0.003) and returned to baseline during recovery. VC was less sensitive than PPG but reproduced the expected hemodynamic profile. A positive correlation was found between venous dilation during recovery and the decrement velocity of microvascular perfusion during occlusion. VC and NIRI represent accessible and complementary tools for assessing vascular responses during PORH. Their combined application may enhance non-invasive vascular evaluation in both clinical and research settings.