Figure 7
From: Examining the challenges of blood pressure estimation via photoplethysmogram
Multi-valued mappings. Examples of PPG waveforms (PPG\(_{i}\) and PPG\(_{j}\)) that are very similar and have corresponding arterial blood pressure waveforms (ABP\(_{i}\) and ABP\(_{j}\)) that are quite different. This highlights the existence of similar features that map to different targets, which makes the task of blood pressure prediction via PPG pulse wave analysis ill-conditioned.
