Abstract
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.
Highlights
Capillary refill time (CRT) is defined as the time taken for a distal capillary bed to regain its colour after blanching caused by external applied pressure
We proposed the incorporation of polymer optical fibre (POF) pulse oximetry with a fibre Bragg grating (FBG) pressure sensor to simultaneously monitor oxygen saturation and the contact force of the subject [25]
In vivo measurements of 10 healthyof volunteers photoplethysmography with an FBG contact pressure sensor capable carryingdemonstrated out measurements potential refill of the sensor to provide quantitative In of the capillary time was demonstrated
Summary
Capillary refill time (CRT) is defined as the time taken for a distal capillary bed to regain its colour after blanching caused by external applied pressure. Recent studies investigating automatic measurement of this process have reported that CRT can be calculated from the changes in the reflected light due to the pressure applied on the skin [13,17,18,19,20,21]. In the present study, this sensor is used to simultaneously monitor the reflectance PPG signals and the applied pressure signals to provide a new method of measuring CRT. In 2017, Shinozaki et al presented a CRT measurement method which modelled the recovery phase of the intensity waveform as an exponential decay, and recorded the time taken for the light intensity to return to 10% of its initial height above baseline after the blanching pressure was released [31].
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