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Introduction
Cardiovascular (CV) diseases, including atherosclerosis and stroke are major public health challenges, consistently ranking among the leading causes of death worldwide in recent decades, especially in the elderly population [1, 2]. Age-related phenotypic alterations in the CV system, and more importantly their accelerated development brought about by CV risk factors, are among the most relevant (patho)physiological changes that drive these diseases [3, 4]. Therefore, identifying new, affordable biomarkers that reflect (CV) aging is critical for improving treatments and preventive strategies.
Peripheral pulse wave analysis may offer a valuable method for monitoring CV health and predicting disease progression [5, 6]. Calculating heart rate from continuous pulse wave recordings may have relevance in diagnostics, as pulse rate variability (PRV) is an important indicator of various diseases [7, 8–9]. Beyond PRV, the morphological characteristics of pulse waves have yielded considerable attention, with numerous studies suggesting that these parameters may be associated with CV disease states such as atherosclerosis and heart failure [5, 10, 11].
Photoplethysmography (PPG) is a simple, easily accessible, and highly repeatable method for real-time monitoring of pulse waves [12]. This non-invasive technique involves illuminating the skin and tissues below, typically the finger, with an LED and measuring the intensity of the reflected or transmitted light, which corresponds to pressure changes in the vascular system. Importantly, PPG has no known adverse effects [13].
The promising results from previous studies suggest that PPG-based pulse wave analysis could gain traction in CV diagnostics and home monitoring in the near future [14]. While it holds potential as a tool for assessing CV aging, its broader use is constrained by the limited investigation of age-related correlations in most PPG-derived parameters. Although some parameters have been linked to age-related changes, most studies have focused on the age dependence of individual or a few selected parameters, leaving the majority unexplored [6, 15, 16–17].
However, a combination of parameters or composite measures derived from multiple parameters might better capture age-related changes than single parameters alone. PPG-based monitoring devices, equipped with advanced algorithms, enable the simultaneous assessment and complex analysis of numerous parameters [5, 18]. Consequently, research aimed at identifying a set of simultaneously recorded PPG features with the strongest correlation to CV age could significantly enhance the potential of PPG-based pulse wave...