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The effects of optical sensor-tissue separation in endocavitary photoplethysmography

Patel, Z., Thaha, M. A. & Kyriacou, P. A. ORCID: 0000-0002-2868-485X (2018). The effects of optical sensor-tissue separation in endocavitary photoplethysmography. Physiological Measurement, 39(7), article number 075001. doi: 10.1088/1361-6579/aacc1d


Objective: Intestinal anastomotic failure that occurs mainly due to ischaemia is a serious risk in colorectal cancer patients undergoing surgery. Surgeons continue to rely on subjective methods such as visual inspection to assess intestinal viability during surgery and there are no clinical tools to directly monitor viability postoperatively. A dual-wavelength reflectance optical sensor has been developed for continuous and dynamic monitoring of intestinal viability via the intestinal lumen. Maintaining direct contact between the sensor and the inner intestinal wall can be difficult in an intraluminal design, therefore impacting on signal acquisition and quality. This paper investigates the effect of direct contact versus variable distances between the sensor and the tissue surface of the buccal mucosa as a surrogate.

Approach: The in vivo study involved 20 healthy volunteers to measure the effect of optical sensor-tissue distances on the ability to acquire photoplethysmography signals and their quality. Signals were acquired from the buccal mucosa at five optical sensor-tissue distances.

Main results: Distances between 0 mm (contact) to 5 mm were the most optimal, producing signals of high quality and signal-to-noise ratio, resulting in reliable estimations of the blood oxygen saturation. Distances exceeding 5 mm compromised the acquired signals, and were of poor quality, thereby unreliably estimating the blood oxygen saturation.

Significance: The developed optical sensor proved to be reliable for acquiring photoplethysmography signals for cases where distances between the optical sensor-tissue may arise during the assessment of intraluminal intestinal viability.

Publication Type: Article
Additional Information: This is an author-created, un-copyedited version of an article accepted for publication/published in Physiological Measurement. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Publisher Keywords: bowel viability, intestine, optical sensor, photoplethysmography, physiological monitoring, pulse oximetry
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering
SWORD Depositor:
[thumbnail of 2018 Z Patel et al. The effects of optical sensor-tissue separation in endocavitary photoplethysmography. Physiol Meas. 2018 Jul 3;39(7) (002).pdf]
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