Optical Fibre Sensor for Simultaneous Measurement of Capillary Refill Time and Contact Pressure

• Main Authors: Chong Liu, Ricardo Correia, Hattan Ballaji, Serhiy Korposh, Barrie Hayes-Gill, Stephen Morgan
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Sensors
• Subjects: capillary refill time; plastic optical fibre; photoplethysmography; fibre bragg grating; contact pressure
• Online Access: https://www.mdpi.com/1424-8220/20/5/1388

The widely applied capillary refill time (CRT) measurement is currently performed by manually applying pressure and using a stopwatch to record the time taken for the skin to recover its normal colour after a blanching pressure is applied. This method is highly subjective and observer-dependent. This paper presents a new, integrated optical sensor probe, combining monitoring of the capillary refilling process with the blanching pressure applied. The sensor consists of an optical fibre-based reflectance photoplethysmography (PPG) sensor to measure the reflected light signal, as well as a fibre Bragg grating (FBG) to measure the applied blanching pressure and to indicate the time when pressure is released. This sensor was applied to calculate the CRT (1.38 ± 0.66 s) of 10 healthy adult volunteers with (55.2 ± 21.8 kPa) blanching pressures. The form of the capillary refilling data was investigated by fitting using an exponential regression model (R² > 0.96). The integrated probe has the potential to improve the reliability of CRT measurements by standardising the optimum duration and magnitude of the pressure.