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.