Swallow-PPG: Photoplethysmography Templates for Comprehensive Temporal Analysis of Swallowing Anatomical Actions

In clinical practice, Videofluoroscopic Swallowing Study (VFSS) is commonly used to monitor the activity of anatomical structures during swallowing. However, it is limited by ionizing radiation exposure, adverse effects of barium contrast agents, and the high cost of specialized equipment. In this study, we propose a framework for analyzing swallowing behaviors in photoplethysmography (PPG) waveforms, which includes generalizing the manifestation of swallowing in PPG (i.e., swallowing templates generation) and conducting comprehensive temporal analysis of swallowing anatomical actions (TASAA). For swallowing templates generation, we cluster and average the samples to obtain waveforms of templates, followed by conducting shape-based mapping and averaging on 28 time indicators to derive template unified time indicators (TUTIs). For comprehensive TASAA, we leverage templates waveforms and TUTIs to estimate time indicators based on the mapping relationship between samples and their respective templates. We evaluate the proposed framework on 357 swallowing PPG samples from 41 elderly subjects. The average relative error across all time indicators is 0.123, and 6 indicators notably excel with errors below 0.1. The proposed template-based swallowing analysis framework is expected to become a low-cost and non-ionizing alternative to VFSS for comprehensive TASAA.