I am a Senior Lecturer (=Associate Professor) in Biomedical Engineering at City, University London and am privileged to work at the interface of three fascinating disciplines: physics, engineering and medicine. Last academic year I was awarded a Senior Research Fellowship awarded jointly from the Royal Academy of Engineering and the Leverhulme Trust, which enabled me to concentrate on research, specifically to solve the problem of measuring intracranial pressure, an important vital sign for head injured patients, using completely non-invasive methods. I am also the Course Director for the MEng/BEng in Biomedical Engineering degree programmes at City. During 2017 I am working as a Visiting Research Scientist at Google in London.I graduated in Physics from Durham University and started my career at Ciba Corning Diagnostics in the UK where I worked for two years on the design and evaluation of prototype biomedical instrumentation. I then worked at the Royal Brompton Hospital and later St Bartholomew's Hospital where I was involved in research in anaesthesia and physiological measurement. I completed my PhD from Queen Mary, University of London for work developing new methods of monitoring cerebral oxygen saturation in head injury patients using fibreoptic sensors. I am a member of the Institute of Physics (IoP), Institute of Physics and Engineering in Medicine (IPEM) and the Institute of Electronic and Electrical Engineers (IEEE). I am also a co-author of Physics in Anaesthesia, a key textbook for medical students and postgraduate trainees studying for their FRCA (Fellow of the Royal College of Anaesthesia) examinations, and rated as 4.6/5 in 19 Amazon reviews.My research is focused on developing new devices and algorithms for non-invasive health monitoring for all levels of healthcare
Background: Photoplethysmography (PPG) sensors, typically found in wrist-worn devices, can contin... more Background: Photoplethysmography (PPG) sensors, typically found in wrist-worn devices, can continuously monitor heart rate (HR) in large populations in real-world settings. Resting heart rate (RHR) is an important biomarker of morbidities and mortality, but no universally accepted definition nor measurement criteria exist. In this study, we provide a working definition of RHR and describe a method for measurement of RHR recorded using PPG derived from wristband measurement across a 24-hour cycle. Methods: 433 healthy subjects wore a wrist device that measured activity and HR for up to 3 months. HR during inactivity was recorded and the duration of inactivity needed for HR to stabilise was ascertained. We identified the lowest HR during each 24-hour cycle (true RHR) and examined the time of day or night this occurred. The variation of HR during inactivity through the 24-hour cycle was also assessed. The sample was also subdivided according to daily activity levels for subset analysis...
Journal of clinical monitoring and computing, Jan 24, 2015
The suitability of different methods of finding the foot point of a pulse as measured using earlo... more The suitability of different methods of finding the foot point of a pulse as measured using earlobe photoplethysmography during stationary conditions was investigated. Instantaneous pulse period (PP) values from PPG signals recorded from the ear in healthy volunteer subjects were compared with simultaneous ECG-derived cardiac periods (RR interval). Six methods of deriving pulse period were used, each based on a different method of finding specific landmark points on the PPG waveform. These methods included maximum and minimum value, maximum first and second derivative, 'intersecting tangents' and 'diastole patching' methods. Selected time domain HRV variables were also calculated from the PPG signals obtained using multiple methods and compared with ECG-derived HRV variables. The correlation between PPG and ECG was greatest for the intersecting tangents method compared to the other methods (RMSEÂ =Â 5.69Â ms, r (2)Â =Â 0.997). No significant differences between PP and RR ...
This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces altera... more This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces alterations in blood flow that contribute to avulsion injury induced pain-like behaviour in rodents. Photoplethysmography (PPG) is an established way of assessing blood flow in the central nervous system (CNS) and laser Doppler flowmetry (LDF) is the most widely used technique for measuring tissue perfusion. Using an established model of SRA injury that produces mechanical hypersensitivity, the PPG and LDF signals were recorded in animals 2 weeks post-injury and compared to naive recordings. PPG and LDF measurements were assessed on the ipsilateral and contralateral sides of the spinal cord rostral and caudal to the avulsion injury and at the level of the injury. Two weeks after injury, a time when vascular blood vessel endothelial markers are known to be decreased, no significant changes were seen in the spinal cord blood flow (SCBF) above, at, or below the injury site or when comparing the i...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2013
The focus of this paper will be in the development and in vivo applications of new custom made ph... more The focus of this paper will be in the development and in vivo applications of new custom made photoplethysmographic (PPG) and pulse oximetry optical and fiber optic sensors and instrumentation in an effort to investigate their suitability in the estimation of blood oxygen saturation and their contribution in the assessment of organ/tissue perfusion and viability. The paper describes the development of optical and fiber optic PPG and blood oxygen saturation (SpO2) sensors and covers examples of application areas including real-time PPG monitoring from body cavities (esophagus) and solid or hollow organs (bowel, liver, stomach, brain, etc). The clinical studies presented successfully demonstrated the feasibility in acquiring PPGs and estimating blood oxygen saturation values from a variety of organs and tissues. The technological developments and the measurements presented in this work pave the way in a new era of pulse oximetry where direct and continuous monitoring of blood oxygen ...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012
Photoplethysmographic (PPG) signals were recorded from the fingers of 10 healthy volunteers durin... more Photoplethysmographic (PPG) signals were recorded from the fingers of 10 healthy volunteers during forced respiratory inspiration. The aim of this pilot study was to assess the effect of negative airway pressure on the blood volumes within the tissue bed of the finger, and the resultant modulation of PPG signals. The acquired signals were analysed and oxygen saturations estimated from the frequency spectra in the cardiac and respiratory frequency ranges. Assuming that respiratory modulation affects blood volumes in veins to a greater extent than in arteries, the local venous oxygen saturation was estimated. Estimated venous oxygen saturation was found to be 3.1% (±4.2%) lower than the estimated arterial saturation.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2011
Novel sensors and instrumentation are currently being investigated with the intended application ... more Novel sensors and instrumentation are currently being investigated with the intended application of determining the concentration of hemoglobin and other optically absorbing compounds in blood using non-invasive methods. In order to measure concentration, the mass or amount of a compound must be known in addition to the volume of liquid. In principle, it may be possible to estimate hemoglobin concentration from a change in optical absorbance occurring over the cardiac cycle divided by a corresponding change in measured blood volume during the cycle measured from peripheral tissue, e.g. the finger or ear. Electrical and optical sensors were evaluated in vitro using a tissue phantom and an absorbing liquid medium. The effect of changes in optical absorption and pulse pressure on the capacitance and optical absorbance were studied.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2010
Computation using Monte Carlo simulations is widely used for modelling the light-tissue interacti... more Computation using Monte Carlo simulations is widely used for modelling the light-tissue interaction. Despite this, many of the methods used for building such simulations are poorly described in the literature. In particular, a scheme for translating the scatter angles produced from a phase function into updated photon direction vectors is not explicitly reported. To address this, a method for calculating the change in photon direction following a scattering event is described, thus illuminating one of the fundamental 'building blocks' for researchers developing their own Monte Carlo models. The equations derived in this paper may be readily incorporated into applicable Monte Carlo program code.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2009
A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating ... more A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating oxygen saturation from the esophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the esophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularized tissue site such as the esophageal epithelium. The value of the mean oxygen saturation recorded from the esophagus was 94.0 +/- 4.0%. These results demonstrate that SpO(2) may be estimated in the esophagus using a fiber-optic probe and this may be the first report of such measurements.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2009
The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventiona... more The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventional pulse oxime-try technology may be compromised by conditions of low tissue perfusion. We have developed a novel 'trans-reflectance' PPG measurement system which combines reflectance and transmit-tance together into a single mode. For comparison purposes the system also enables the independent display of reflectance and transmittance PPG signals simultaneously. Preliminary experiments were performed on volunteers to assess the performance of the probe, where, artificial hypoperfusion was created in individuals and data was recorded with the newly developed trans-reflectance photoplethysmographic mode, and the conventional transmittance and reflectance PPG modes. The PPG signals recorded during hypoperfusion using the trans-reflectance mode were of good quality with higher signal-to-noise ratio than those obtained from the transmittance and reflectance modes.
Background: Photoplethysmography (PPG) sensors, typically found in wrist-worn devices, can contin... more Background: Photoplethysmography (PPG) sensors, typically found in wrist-worn devices, can continuously monitor heart rate (HR) in large populations in real-world settings. Resting heart rate (RHR) is an important biomarker of morbidities and mortality, but no universally accepted definition nor measurement criteria exist. In this study, we provide a working definition of RHR and describe a method for measurement of RHR recorded using PPG derived from wristband measurement across a 24-hour cycle. Methods: 433 healthy subjects wore a wrist device that measured activity and HR for up to 3 months. HR during inactivity was recorded and the duration of inactivity needed for HR to stabilise was ascertained. We identified the lowest HR during each 24-hour cycle (true RHR) and examined the time of day or night this occurred. The variation of HR during inactivity through the 24-hour cycle was also assessed. The sample was also subdivided according to daily activity levels for subset analysis...
Journal of clinical monitoring and computing, Jan 24, 2015
The suitability of different methods of finding the foot point of a pulse as measured using earlo... more The suitability of different methods of finding the foot point of a pulse as measured using earlobe photoplethysmography during stationary conditions was investigated. Instantaneous pulse period (PP) values from PPG signals recorded from the ear in healthy volunteer subjects were compared with simultaneous ECG-derived cardiac periods (RR interval). Six methods of deriving pulse period were used, each based on a different method of finding specific landmark points on the PPG waveform. These methods included maximum and minimum value, maximum first and second derivative, 'intersecting tangents' and 'diastole patching' methods. Selected time domain HRV variables were also calculated from the PPG signals obtained using multiple methods and compared with ECG-derived HRV variables. The correlation between PPG and ECG was greatest for the intersecting tangents method compared to the other methods (RMSEÂ =Â 5.69Â ms, r (2)Â =Â 0.997). No significant differences between PP and RR ...
This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces altera... more This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces alterations in blood flow that contribute to avulsion injury induced pain-like behaviour in rodents. Photoplethysmography (PPG) is an established way of assessing blood flow in the central nervous system (CNS) and laser Doppler flowmetry (LDF) is the most widely used technique for measuring tissue perfusion. Using an established model of SRA injury that produces mechanical hypersensitivity, the PPG and LDF signals were recorded in animals 2 weeks post-injury and compared to naive recordings. PPG and LDF measurements were assessed on the ipsilateral and contralateral sides of the spinal cord rostral and caudal to the avulsion injury and at the level of the injury. Two weeks after injury, a time when vascular blood vessel endothelial markers are known to be decreased, no significant changes were seen in the spinal cord blood flow (SCBF) above, at, or below the injury site or when comparing the i...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2013
The focus of this paper will be in the development and in vivo applications of new custom made ph... more The focus of this paper will be in the development and in vivo applications of new custom made photoplethysmographic (PPG) and pulse oximetry optical and fiber optic sensors and instrumentation in an effort to investigate their suitability in the estimation of blood oxygen saturation and their contribution in the assessment of organ/tissue perfusion and viability. The paper describes the development of optical and fiber optic PPG and blood oxygen saturation (SpO2) sensors and covers examples of application areas including real-time PPG monitoring from body cavities (esophagus) and solid or hollow organs (bowel, liver, stomach, brain, etc). The clinical studies presented successfully demonstrated the feasibility in acquiring PPGs and estimating blood oxygen saturation values from a variety of organs and tissues. The technological developments and the measurements presented in this work pave the way in a new era of pulse oximetry where direct and continuous monitoring of blood oxygen ...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012
Photoplethysmographic (PPG) signals were recorded from the fingers of 10 healthy volunteers durin... more Photoplethysmographic (PPG) signals were recorded from the fingers of 10 healthy volunteers during forced respiratory inspiration. The aim of this pilot study was to assess the effect of negative airway pressure on the blood volumes within the tissue bed of the finger, and the resultant modulation of PPG signals. The acquired signals were analysed and oxygen saturations estimated from the frequency spectra in the cardiac and respiratory frequency ranges. Assuming that respiratory modulation affects blood volumes in veins to a greater extent than in arteries, the local venous oxygen saturation was estimated. Estimated venous oxygen saturation was found to be 3.1% (±4.2%) lower than the estimated arterial saturation.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2011
Novel sensors and instrumentation are currently being investigated with the intended application ... more Novel sensors and instrumentation are currently being investigated with the intended application of determining the concentration of hemoglobin and other optically absorbing compounds in blood using non-invasive methods. In order to measure concentration, the mass or amount of a compound must be known in addition to the volume of liquid. In principle, it may be possible to estimate hemoglobin concentration from a change in optical absorbance occurring over the cardiac cycle divided by a corresponding change in measured blood volume during the cycle measured from peripheral tissue, e.g. the finger or ear. Electrical and optical sensors were evaluated in vitro using a tissue phantom and an absorbing liquid medium. The effect of changes in optical absorption and pulse pressure on the capacitance and optical absorbance were studied.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2010
Computation using Monte Carlo simulations is widely used for modelling the light-tissue interacti... more Computation using Monte Carlo simulations is widely used for modelling the light-tissue interaction. Despite this, many of the methods used for building such simulations are poorly described in the literature. In particular, a scheme for translating the scatter angles produced from a phase function into updated photon direction vectors is not explicitly reported. To address this, a method for calculating the change in photon direction following a scattering event is described, thus illuminating one of the fundamental 'building blocks' for researchers developing their own Monte Carlo models. The equations derived in this paper may be readily incorporated into applicable Monte Carlo program code.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2009
A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating ... more A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating oxygen saturation from the esophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the esophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularized tissue site such as the esophageal epithelium. The value of the mean oxygen saturation recorded from the esophagus was 94.0 +/- 4.0%. These results demonstrate that SpO(2) may be estimated in the esophagus using a fiber-optic probe and this may be the first report of such measurements.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2009
The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventiona... more The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventional pulse oxime-try technology may be compromised by conditions of low tissue perfusion. We have developed a novel 'trans-reflectance' PPG measurement system which combines reflectance and transmit-tance together into a single mode. For comparison purposes the system also enables the independent display of reflectance and transmittance PPG signals simultaneously. Preliminary experiments were performed on volunteers to assess the performance of the probe, where, artificial hypoperfusion was created in individuals and data was recorded with the newly developed trans-reflectance photoplethysmographic mode, and the conventional transmittance and reflectance PPG modes. The PPG signals recorded during hypoperfusion using the trans-reflectance mode were of good quality with higher signal-to-noise ratio than those obtained from the transmittance and reflectance modes.
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