Publications

@article{Ballaji2020-wp,

title = {A textile sleeve for monitoring oxygen saturation using 

 multichannel optical fibre photoplethysmography},

author = {Hattan K Ballaji and Ricardo Correia and Serhiy Korposh and Barrie R Hayes-Gill and Francisco U Hernandez and Byron Salisbury and Stephen P Morgan},

year  = {2020},

date = {2020-11-01},

journal = {Sensors (Basel)},

volume = {20},

number = {22},

pages = {6568},

publisher = {MDPI AG},

abstract = {Textile-based systems are an attractive prospect for wearable 

 technology as they can provide monitoring of key physiological 

 parameters in a comfortable and unobtrusive form. A novel system 

 based on multichannel optical fibre sensor probes integrated 

 into a textile sleeve is described. The system measures the 

 photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), 

 which is then used to calculate oxygen saturation (SpO2). In 

 order to achieve reliable measurement without adjusting the 

 position of the garment, four plastic optical fibre (POF) probes 

 are utilised to increase the likelihood that a high-quality PPG 

 is obtained due to at least one of the probes being positioned 

 over a blood vessel. Each probe transmits and receives light 

 into the skin to measure the PPG and SpO2. All POFs are 

 integrated in a stretchable textile sleeve with a circumference 

 of 15 cm to keep the sensor in contact with the subject's wrist 

 and to minimise motion artefacts. Tests on healthy volunteers 

 show that the multichannel PPG sensor faithfully provides an 

 SpO2 reading in at least one of the four sensor channels in all 

 cases with no need for adjusting the position of the sleeve. 

 This could not be achieved using a single sensor alone. The 

 multichannel sensor is used to monitor the SpO2 of 10 

 participants with an average wrist circumference of 16.0 $±$ 

 0.6 cm. Comparing the developed sensor's SpO2 readings to a 

 reference commercial oximeter (reflectance Masimo Radical-7) 

 illustrates that the mean difference between the two sensors' 

 readings is -0.03%, the upper limit of agreement (LOA) is 

 0.52% and the lower LOA is -0.58%. This multichannel sensor 

 has the potential to achieve reliable, unobtrusive and 

 comfortable textile-based monitoring of both heart rate and SpO2 

 during everyday life.},

keywords = {multichannel, oxygen saturation, photoplethysmography, plastic   optical fibre, textile, wearable technology},

pubstate = {published},

tppubtype = {article}

}

@article{Liu2020-xk,

title = {Optical fibre sensor for simultaneous measurement of capillary 

 refill time and contact pressure},

author = {Chong Liu and Ricardo Correia and Hattan Ballaji and Serhiy Korposh and Barrie Hayes-Gill and Stephen Morgan},

year  = {2020},

date = {2020-03-01},

journal = {Sensors (Basel)},

volume = {20},

number = {5},

pages = {1388},

publisher = {MDPI AG},

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.},

keywords = {Capillary refill time, contact pressure, fibre bragg grating, photoplethysmography, plastic optical fibre},

pubstate = {published},

tppubtype = {article}

}