Induced pain affects auricular and body biosignals: From cold stressor to deep breathing

Andrius Rapalis; Povilas Piartli; Lina Jankauskaitė; Vaidotas Marozas; Eugenijus Kaniusas

doi:10.3389/fphys.2023.1090696

Induced pain affects auricular and body biosignals: From cold stressor to deep breathing

Front Physiol. 2023 Jan 17:14:1090696. doi: 10.3389/fphys.2023.1090696. eCollection 2023.

Authors

Andrius Rapalis^{1

2}, Povilas Piartli¹, Lina Jankauskaitė^{3

4}, Vaidotas Marozas^{1

2}, Eugenijus Kaniusas⁵

Affiliations

¹ Biomedical Engineering Institute, Kaunas University of Technology, Kaunas, Lithuania.
² Department of Electronics Engineering, Faculty of Electrical and Electronics Engineering, Kaunas University of Technology, Kaunas, Lithuania.
³ Department of Pediatrics, Faculty of Medicine, Medical Academy, Lithuanian University of Health Sciences, Kaunas, Lithuania.
⁴ Institute of Physiology and Pharmacology, Medical Academy, Lithuanian University of Health Sciences Kauno Klinikos, Kaunas, Lithuania.
⁵ Institute of Biomedical Electronics, Faculty of Electrical Engineering and Information Technology, Vienna University of Technology (TU Wien), Vienna, Austria.

Abstract

Pain affects every fifth adult worldwide and is a significant health problem. From a physiological perspective, pain is a protective reaction that restricts physical functions and causes responses in physiological systems. These responses are accessible for evaluation via recorded biosignals and can be favorably used as feedback in active pain therapy via auricular vagus nerve stimulation (aVNS). The aim of this study is to assess the significance of diverse parameters of biosignals with respect to their deflection from cold stressor to deep breathing and their suitability for use as biofeedback in aVNS stimulator. Seventy-eight volunteers participated in two cold pressors and one deep breathing test. Three targeted physiological parameters (RR interval of electrocardiogram, cardiac deflection magnitude Z _AC of ear impedance signal, and cardiac deflection magnitude PPG _AC of finger photoplethysmogram) and two reference parameters (systolic and diastolic blood pressures BP _S and BP _D) were derived and monitored. The results show that the cold water decreases the medians of targeted parameters (by 5.6, 9.3%, and 8.0% of RR, Z _AC, and PPG _AC, respectively) and increases the medians of reference parameters (by 7.1% and 6.1% of BP _S and BP _D, respectively), with opposite changes in deep breathing. Increasing pain level from relatively mild to moderate/strong with cold stressor varies the medians of targeted and reference parameters in the range from 0.5% to 6.0% (e.g., 2.9% for RR, Z _AC and 6.0% for BP _D). The physiological footprints of painful cold stressor and relaxing deep breathing were shown for auricular and non-auricular biosignals. The investigated targeted parameters can be used as biofeedback to close the loop in aVNS to personalize the pain therapy and increase its compliance.

Keywords: auricular bioimpedance; auricular vagus nerve stimulation; blood pressure; cold pressor test; deep breathing; photoplethysmography; physiological biofeedback.

Grants and funding

This research was funded by the Research and Innovation Fund of Kaunas University of Technology (project grant No. PP2021/5) and the Research Fund of Lithuanian University of Health Sciences (2021-JV-00006). This study received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 880603 (SzeleSTIM GmbH). The funder SzeleSTIM GmbH had the following involvement with the study: the study design and collection of data. All authors declare no other competing interests.