Monitoring Autonomic Tone During Spinal Cord Neuromodulation Using Wearable AURIS Sensor

The transition of bioelectronic medicine to clinical use is currently limited by a lack of non-invasive sensors capable of measuring autonomic tone during active neuromodulation. Conventional monitoring modalities, such as mean arterial pressure (MAP) and Ag/AgCl chest electrodes, are often invasive, cumbersome, or susceptible to motion artifacts. Here, we present a novel framework employing an in-ear sensor (AURIS) to continuously monitor heart rate variability (HRV) during therapeutic neuromodulation. These sensors utilize a polydimethylsiloxane (PDMS) substrate to ensure biocompatibility and superior conformability. Experiments in a rodent model (n = 3) demonstrate that the AURIS platform achieves gold-standard fidelity, with mean heart rate differences of 6.03 BPM and mean RR interval deltas of 3.18 ms compared to chest electrodes. Sensor agreement was statistically validated using independent t-tests, showing no significant difference between modalities (all p > 0.46). While time-domain shifts trended toward significance, complexity metrics showed robust sequential responses with large effect sizes, including the SD1/SD2 ratio (d = 1.474) and the DFA α ratio (d = 1.091). These findings validate a sensor architecture that is durable, accessible, and provides the necessary technical foundation for closed-loop feedback and non-invasive clinical trials.