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

Area of Science:

• Physiology
• Biomedical Engineering
• Medical Imaging

Background:

• Post-occlusive reactive hyperemia (PORH) is a key indicator of microvascular function, typically assessed using optical methods.
• Existing methods for characterizing PORH often lack cost-effectiveness or fail to capture venous dynamics.
• Low-cost imaging techniques like photoplethysmography (PPG), videocapillaroscopy (VC), and near-infrared reflectance imaging (NIRI) offer potential for complementary insights into vascular responses.

Purpose of the Study:

• To evaluate the utility of low-magnification videocapillaroscopy (VC) and near-infrared reflectance imaging (NIRI) for quantifying perfusion changes during post-occlusive reactive hyperemia (PORH).
• To compare the performance of VC and NIRI against photoplethysmography (PPG) as a reference method in healthy subjects.
• To explore the combined application of VC and NIRI for comprehensive non-invasive vascular assessment.

Main Methods:

• A standardized PORH protocol involving suprasystolic arterial occlusion was applied to 14 healthy participants.
• Simultaneous recordings were obtained using PPG (finger), VC (finger), and NIRI (dorsal hand veins).
• Skin blood flow, hemoglobin index (C_Hb), and vein width were quantified to assess microvascular and venous dynamics during baseline, occlusion, and recovery phases.

Main Results:

• Arterial occlusion led to significant reductions in skin blood flow (-95.3%) and C_Hb (-8.3%), with less pronounced contralateral effects.
• Vein width significantly increased during occlusion and returned to baseline post-occlusion.
• Videocapillaroscopy showed lower sensitivity than PPG but successfully reflected the expected hemodynamic changes; a correlation was observed between venous dilation and microvascular perfusion decrement velocity.

Conclusions:

• Videocapillaroscopy and near-infrared reflectance imaging are accessible and complementary tools for evaluating vascular responses during post-occlusive reactive hyperemia.
• The combined use of VC and NIRI can enhance non-invasive vascular assessment in both research and clinical settings.
• These low-cost imaging modalities provide valuable insights into microvascular and venous dynamics during PORH.