Bioelectrical Impedance Analysis of Thermal-Induced Cutaneous Nociception

Objective: People perceive different levels of pain at the same stimulus intensity, hence overburdening objective nociception assessment. In the context of recently developed pain monitors, this work presents the analysis of the complex bioimpedance measured during cold-induced cutaneous nociception. Using the Anspec-PRO device, this analysis results in a more complex characterization of the acquired signal (i.e., 3 -dimensional or image-based representations), rather than evaluations of one/multiple single-dimension signals (i.e., time-based index). Methods: The experimental protocol consists of thermal testing the nociception response of 13 participants, in terms of impedance changes. Several study cases are performed to evaluate the bioimpedance variability over one day, day to day, and at different stimulus intensities. Results: The measured bioimpedance fluctuations in time were validated against the self-reported pain level of the test subjects. Moreover, the bioimpedance, acting as the frequency response of cold-induced nociception, demonstrated the pain memory effect and the influence on the impedance of the liquid/fat in the body. Conclusion: The impedance analysis can delineate cold-induced nociception effects from nominal states, the impedance spectroscopy proving the potential to monitor the evoked pain. Significance: The implications of this work rely on advancing the state of art for pain detection by using time- frequency analysis and image-based information. Moreover, in closed-loop anesthesia control, the nociception surrogate monitoring provides direct feedback for analgesia and an input-output model to opioids.