Abstract
The ankle-brachial index (ABI) is the most non-invasive technique used for diagnosing and assessing peripheral artery disease (PAD), although it is operator-dependent and limited by arterial calcification. Since photoplethysmography (PPG) is a non-invasive, low-cost, and easy-to-use technique that is not limited by arterial compressibility, PPG morphological parameters have been studied for PAD diagnosis, mostly based on mean values. In this work, the relationship between variability indices of PPG morphological parameters and ABI was studied in 52 legs of 32 PAD patients. The morphological PPG parameters, including amplitude, pulse transit time (PTT), and maximum systolic slope, were measured. The mean, standard deviation, and frequency spectral energy for very low, low, and high frequencies were computed as PPG morphological variability indices. The variability indices of PPG morphological parameters have a significant correlation with ABI, indicating that they differ not only between legs with altered and normal ABI but also that they may relate to PAD progression. Fourteen of the 15 variability indices showed significant diagnostic value, with the standard deviation of PTT being the most effective (sensitivity of 96% and specificity of 71%). The differences between normal and non-compressible legs were not significant. The comparison between contralateral legs was also not significant. This suggests that variability indices may provide valuable insights into changes in physiological regulatory mechanisms as PAD progresses, which could aid in the diagnosis, assessment, and prognosis of PAD in future research.