Flexible, Implantable, Pulse Oximetry Sensors: Toward Long-Term Monitoring of Blood Oxygen Saturations

Abstract

Pulse oximetry is the most widespread method of monitoring heart rate and blood oxygen levels in both clinical and non-clinical settings. Current devices are ridged, bulky, and suitable only for short-term use. While the next generation of devices are moving toward wearable technologies, this focus on being unobtrusive is insufficient. To enable continuous high quality long-term monitoring, implanted devices are required. These will eliminate interference from light and sensitivity to skin pigmentation, allow enhanced performance during movement, and have no concerns around percussive damage. Here, an inexpensive, ultra-flexible pulse oximetry probe is demonstrated. The hybrid devices are fabricated on 5 µm Parylene C using laser ablation to define the circuit, and integrate small, rigid optoelectronic components. These are demonstrated in vivo on anesthetized pigs. Both transmission mode, and the novel reflection mode, are shown to be effective geometries for this. The heart rate measured by these devices shows < 2% variance from concurrent peripheral pulse oximetry measurements, along with an average variance of around 2.5% attributed predominantly to differences between central and peripheral oxygen saturations. In addition, it is shown that when implemented directly on the femoral artery, these devices record a more acute response to the variation in oxygen intake compared to the peripheral measurements. Finally, the same devices are shown to have the potential for use in monitoring venous oxygen content. This could open up the possibility of continuous monitoring of arteriovenous oxygen difference. These devices are straightforward to produce, biocompatible, and can be easily implanted during cardiovascular surgery, offering a route toward long-term implantation for continuous patient monitoring.