Proof of Concept of a Novel Neck-Situated Wearable PPG System for Continuous Physiological Monitoring

Continuous overnight vital signs monitoring would be ideal for patients suffering from epilepsy, where life-threatening hypoxemias can occur during sleep. However, the existing physiological monitoring systems suffer from limitations in terms of usability factors and/or limited information of the signals being acquired. The body location of the monitoring system is a crucial consideration, seldom addressed by the wider community. This article presents a proof-of-concept, neck-worn photoplethysmography system, which was developed and tested to assess the feasibility of the neck as a monitoring site for longitudinal sensing of cardiac and respiratory responses during sleep. The novel system was compared against a gold-standard commercial multichannel cardiorespiratory polysomnography (PSG) system during oxygen desaturation cycles, to assess its ability to measure heart rate, respiratory rate (RR), and peripheral blood oxygen saturation (SpO₂) on 15 participants. The findings for heart rate showed a marginal mean error of 0.47 beats/min with limits of agreement (LOA) at 95% confidence between −3.17 and 4 bpm. RR comparisons had an overall mean error of 0.43 breaths/min, with LOA at 95% confidence between −2.73 and 3.3 bpm. Lastly, the system accurately outputs SpO₂ with an overall root-mean-square error of 1.44% between 90 and 100% SpO₂ using a custom calibration method. Moreover, it was observed that the neck made it possible for the system to detect desaturation events on an average 12.6 s prior to the PSG system, which used a peripheral finger-based PPG system. Ultimately, this proof-of-concept study illustrates the viability of neck-based sensing for minimally invasive monitoring of cardiac and respiratory vitals during sleep.