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. 2021 Oct 1;3(10):e0539. doi: 10.1097/CCE.0000000000000539

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Copyright © 2021 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

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Figure 2. — Representative respiratory non-invasive venous waveform analysis (RIVA) respiratory signals from subjects with low risk to high risk of oxygen support need (left to right). Raw signals are transformed from the time domain (top) to the frequency domain (bottom) (1). The relative amplitude of the respiratory rate (fundamental frequency of the respiratory rate [f_R0]) compared with the relative amplitude of the pulse rate (fundamental frequency of the pulse rate [f₀]) is used to calculate a RIVA respiratory index (RIVA-RI). COVID-19 = coronavirus disease 2019.