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. 2020 Sep 22;8(9):e20488. doi: 10.2196/20488

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©Asim H Gazi, Nil Z Gurel, Kristine L S Richardson, Matthew T Wittbrodt, Amit J Shah, Viola Vaccarino, J Douglas Bremner, Omer T Inan. Originally published in JMIR mHealth and uHealth (http://mhealth.jmir.org), 22.09.2020.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR mHealth and uHealth, is properly cited. The complete bibliographic information, a link to the original publication on http://mhealth.jmir.org/, as well as this copyright and license information must be included.

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Physiological sensing, signal processing, and modeling preparation. Twenty-four subjects (12 active) underwent a clinical protocol, wherein the electrocardiogram (ECG) was measured with electrodes placed in a three-lead configuration and the photoplethysmogram (PPG) was measured from the fingertip in a transmissive LED-photodiode setup. Transcutaneous cervical vagus nerve stimulation (tcVNS) or sham stimulation was administered at predefined times, where the exact stimulation location was identified by locating the left carotid pulse. Following signal processing and biomarker extraction, the biomarkers were prepared for modeling via 5-point causal averaging, resampling to 1 Hz, normalizing to rest, and finally parsing into 4 separate vectors associated with the 4 tcVNS/sham administrations studied. By referencing stimulation initiation, the corresponding input amplitude waveforms were then constructed to replicate device administration. Amp.: amplitude; D1: day 1; D2: day 2; D3: day 3.