Camera-based assessment of hemodynamics for non-contact blood pressure estimation

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The project aims at the non-contact blood pressure estimation by using cameras. To that end, we develop generally applicable methods to assess the hemodynamic function from videos and evaluate the proposed methods and their feasibility for blood pressure estimation, respectively, within systematic experiments.Recent works proved (1) that the heart activity multimodally, i.e. by the blood volume pulse and ballistocardiographic effects, affects video recordings and (2) that video recordings allow the spatio-temporal assessment of blood pulsations. We exploit both aspects to derive parameters related to the proximal (via ballistocardiography) and distal (via pulse wave arrival and pulse wave propagation) cardiovascular activity and estimate the beat-to-beat blood pressure from such parameters. Within the project, we firstly develop methods to extract shape-preserved, i.e. morphologically usable, photoplethysmograms (cbPPG) and ballistocardiograms (cbBCG) from videos. The proposed methods make use of spatio-temporal averaging using a non-linear algorithm for signal warping (two-dimensional signal warping). Based on spatially resolved cbPPG, we develop a novel method to estimate the peripheral vascular tone using videos (the so-called perfusion velocity). The perfusion velocity is gained by a probabilistic approach, which determines spatially resolved probability distributions of the peripheral pulse wave velocity and estimates the perfusion velocity from the superposition of local distributions. To eventually estimate the blood pressure, we combine the pulse transit time, which is derived from cbBCG and cbPPG, and the partially complementary perfusion velocity within a multilevel analysis and determine a model for non-contact blood pressure estimation. To validate the proposed methods, we conduct an experimental study comprising 50 healthy subjects undergoing an experimental protocol that was developed for the project. As a result, the project provides methods for the non-contact assessment of hemodynamic characteristics using cameras. Such methods can be applied to estimate the beat-to-beat blood pressure, but even beyond blood pressure estimation, they offer wide opportunities to assess the perfusion and autonomous regulation. Our basic investigations further make a major contribution to characterize the opportunities and limitations of camera-based assessment of vital parameters, particularly related to the spatio-temporal characteristics of pulse wave propagation.