{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,24]],"date-time":"2026-01-24T01:23:24Z","timestamp":1769217804721,"version":"3.49.0"},"reference-count":39,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2021,9,10]],"date-time":"2021-09-10T00:00:00Z","timestamp":1631232000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000266","name":"Engineering and Physical Sciences Research Council","doi-asserted-by":"publisher","award":["EP\/R511730\/1"],"award-info":[{"award-number":["EP\/R511730\/1"]}],"id":[{"id":"10.13039\/501100000266","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Nottingham Hospitals Charity Research Fund","award":["na"],"award-info":[{"award-number":["na"]}]},{"name":"Saudi Arabia Ministry of Higher Education","award":["na"],"award-info":[{"award-number":["na"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Capillary refill time (CRT) refers to the time taken for body tissue to regain its colour after an applied blanching pressure is released. Usually, pressure is manually applied and not measured. Upon release of pressure, simple mental counting is typically used to estimate how long it takes for the skin to regain its colour. However, this method is subjective and can provide inaccurate readings due to human error. CRT is often used to assess shock and hydration but also has the potential to assess peripheral arterial disease which can result in tissue breakdown, foot ulcers and ultimately amputation, especially in people with diabetes. The aim of this study was to design an optical fibre sensor to simultaneously detect blood volume changes and the contact pressure applied to the foot. The CRT probe combines two sensors: a plastic optical fibre (POF) based on photoplethysmography (PPG) to measure blood volume changes and a fibre Bragg grating to measure skin contact pressure. The results from 10 healthy volunteers demonstrate that the blanching pressure on the subject\u2019s first metatarsal head of the foot was 100.8 \u00b1 4.8 kPa (mean and standard deviation), the average CRT was 1.37 \u00b1 0.46 s and the time to achieve a stable blood volume was 4.77 \u00b1 1.57 s. For individual volunteers, the fastest CRT measured was 0.82 \u00b1 0.11 and the slowest 1.94 \u00b1 0.49 s. The combined sensor and curve fitting process has the potential to provide increased reliability and accuracy for CRT measurement of the foot in diabetic foot ulcer clinics and in the community.<\/jats:p>","DOI":"10.3390\/s21186072","type":"journal-article","created":{"date-parts":[[2021,9,12]],"date-time":"2021-09-12T21:48:01Z","timestamp":1631483281000},"page":"6072","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Optical Fibre Sensor for Capillary Refill Time and Contact Pressure Measurements under the Foot"],"prefix":"10.3390","volume":"21","author":[{"given":"Hattan K.","family":"Ballaji","sequence":"first","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"},{"name":"Computer Engineering Department, College of Computers and Information System, Umm Al-Qura University, Makkah 24381, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6405-5340","authenticated-orcid":false,"given":"Ricardo","family":"Correia","sequence":"additional","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2340-4329","authenticated-orcid":false,"given":"Chong","family":"Liu","sequence":"additional","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5179-6991","authenticated-orcid":false,"given":"Serhiy","family":"Korposh","sequence":"additional","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4237-7001","authenticated-orcid":false,"given":"Barrie R.","family":"Hayes-Gill","sequence":"additional","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alison","family":"Musgrove","sequence":"additional","affiliation":[{"name":"Nottingham University Hospitals NHS Trust, Nottingham NG5 1PB, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4069-3801","authenticated-orcid":false,"given":"Stephen P.","family":"Morgan","sequence":"additional","affiliation":[{"name":"Optics and Photonics Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,9,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1136\/archdischild-2013-305198","article-title":"How to use capillary refill time","volume":"99","author":"King","year":"2014","journal-title":"Arch. 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