The plantar-palmar index with near infrared spectroscopy as an alternative to the ankle-brachial index for non-invasive evaluation of vascular perfusion and peripheral arterial disease

Abstract

Aims: Peripheral arterial disease (PAD) contributes to significant morbidity, particularly in diabetic and high-risk vascular populations. While the ankle-brachial index (ABI) remains a diagnostic cornerstone, it exhibits poor sensitivity in patients with vascular calcification or diabetes. Near-infrared spectroscopy (NIRS), paired with a novel plantar-palmar index (PPI), offers a point-of-care, non-invasive, and real-time method for assessing tissue perfusion. This study evaluates the clinical correlation between the NIRS-derived PPI and pulse volume recordings (PVR), supporting its role as a replacement for ABI. Methods: A prospective observational study was conducted on 91 limbs across 48 participants. Each limb underwent ABI and PVR testing, and NIRS imaging to measure corresponding oxygen saturation (StO2) values. The PPI was calculated as the ratio of plantar StO2 to palmar StO2. PPI values were compared across PVR-defined disease states using ANOVA with pairwise comparisons. Results: Estimated margin means for PPI increased with disease severity: normal (1.054), mild (1.178), moderate (1.376), and severe (1.430). PPI significantly distinguished normal from all PAD classes (p<0.005). NIRS imaging demonstrated clear perfusion patterns aligned with PVR classification. Conclusion: PPI derived from NIRS strongly correlates with PVR and offers a viable, non-invasive alternative to ABI, particularly in populations where interpretation of ABI is limited. Broader clinical implementation could redefine vascular screening strategies.