Publications by Professor John Allen - ePrints

Browsing publications by Professor John Allen.

Newcastle Authors	Title	Year
Dr James Frith Dr Jake Gibbon Professor John Allen	The effect of lower limb strengthening exercise on orthostatic blood pressure and the skeletal muscle pump in older people with orthostatic hypotension	2024
Dr Sadaf Iqbal Professor Jaume Bacardit Dr Bridget Griffiths Professor John Allen	Deep learning classification of systemic sclerosis from multi-site photoplethysmography signals	2023
Dr Shahid Iqbal Professor Jaume Bacardit Dr Bridget Griffiths Professor John Allen	Deep learning classification of systemic sclerosis from multi-site photoplethysmography signals.	2023
Sadaf Iqbal Dr Sharad Agarwal Emeritus Professor Alan Murray Professor Jaume Bacardit Professor John Allen et al.	Deep learning identification of coronary artery disease from bilateral finger photoplethysmography sensing: A proof-of-concept study	2023
Professor Gerard Stansby Dr Andrew Sims Lesley Wilson Dr Thomas Beale Ina Guri et al.	Prospective Assessment of the Diagnostic Accuracy of Multi-site Photoplethysmography Pulse Measurements for Diagnosis of Peripheral Artery Disease in Primary Care	2023
Professor John Allen Professor Gerard Stansby	The 2023 wearable photoplethysmography roadmap.	2023
Professor John Allen	Usability and Preliminary Efficacy of an Artificial Intelligence–Driven Platform Supporting Dietary Management in Diabetes: Mixed Methods Study	2023
Professor John Allen	Assessing hemodynamics from the photoplethysmogram to gain insights into vascular age: a review from VascAgeNet	2022
Professor John Allen	Ethnic disparities in publicly-available pulse oximetry databases	2022
Professor John Allen	Novel pulse device for diagnosis of peripheral arterial disease (NOTEPAD)	2022
Professor John Allen	The science and scientists of Don't Look Up, low cost optical technique is improving healthcare.	2022
Samuel Huthart Crispian Oates Professor John Allen Kathia Fiaschi Dr Andrew Sims et al.	Validation of a standardised duplex ultrasound classification system for the reporting and grading of peripheral arterial disease	2022
Professor John Allen	Deep learning based photoplethysmography classification for peripheral arterial disease detection: a proof of concept study	2021
Professor John Allen	Filtering-induced time shifts in photoplethysmography pulse features measured at different body sites: the importance of filter definition and standardization	2021
Professor John Allen	Low frequency variability in photoplethysmography and autonomic function assessment	2021
Professor John Allen Dr Ding Chang Zheng	Photoplethysmography (PPG): state-of-the-art methods and applications	2021
Professor John Allen	Photoplethysmography for the assessment of peripheral vascular disease	2021
Professor John Allen	Photoplethysmography signal processing and synthesis	2021
Professor John Allen	Photoplethysmography: Technology, Signal Analysis and Applications	2021
Dr Luke Boylan Dr Craig Nesbitt Lesley Wilson Professor John Allen Dr Andrew Sims et al.	Reliability of the Edinburgh Claudication Questionnaire for Identifying Symptomatic PAD in General Practice	2021
Professor John Allen	The power of light in medicine - challenges and opportunities in vascular optics	2021
Dr Daniel Kyle Dr Luke Boylan Lesley Wilson Dr Shona Haining Dr Andrew Sims et al.	Accuracy of Peripheral Arterial Disease Registers in UK General Practice: Case-Control Study	2020
Samuel Huthart Professor Gerard Stansby Professor John Allen	Advancing PPG signal quality and know-how through knowledge translation - from experts to student and researcher	2020
Professor John Allen Emeritus Professor Alan Murray	Age related changes in pulse risetime measured by photoplethysmography	2020
Professor John Allen	Assessment of hypertension using clinical electrocardiogram features: A first-ever review	2020
Dr Dingchang Zheng Professor John Allen	Cuffless Single-Site Photoplethysmography for Blood Pressure Monitoring	2020
Professor John Allen	Multi-modal photoplethysmography-based approaches for improved detection of hypertension	2020
Professor John Allen	PPG Synth: An innovative toolbox for synthesizing regular and irregular photoplethysmography waveforms.	2020
Audrey Macdonald Professor John Allen	Between visit variability of thermal imaging of feet in people attending podiatric clinics with diabetic neuropathy at high risk of developing foot ulcers	2019
Professor John Allen	Focus collection on thermal imaging in medicine	2019
Professor John Allen Dr Nicola Leech	Infrared thermography and ulcer prevention in the high‐risk diabetic foot: data from a single‐blind multicentre controlled clinical trial	2019
Professor John Allen	Multi-Site Photoplethysmography Technology for Blood Pressure Assessment: Challenges and Recommendations	2019
Dr Gregory Maniatopoulos Dr Shona Haining Professor John Allen Dr Scott Wilkes	Negotiating commissioning pathways for the successful implementation of innovative health technology in primary care	2019
Dr Nikki Rousseau Jan Lecouturier Professor Gerard Stansby Professor John Allen	Nurses’ and patients’ experiences and preferences of the ankle-brachial pressure index and multi-site photoplethysmography for the diagnosis of peripheral arterial disease: A qualitative study	2019
Jan Lecouturier Dr Jason Scott Dr Nicolette Rousseau Professor Gerard Stansby Dr Andrew Sims et al.	Peripheral arterial disease diagnosis and management in primary care: a qualitative study	2019
Professor John Allen	Quantifying the delays between multi-site photoplethysmography pulse and ECG R-R interval changes under slow paced breathing.	2019
Professor John Allen Dr Ding Chang Zheng	Recent development of respiratory rate measurement technologies	2019
Professor John Allen Dr Thomas Beale Dr Jim Wightman	Sensor Housing and Associated Disposable Element	2019
Professor John Allen Stephen Hedley	Simple photoplethysmography pulse encoding technique for communicating the detection of peripheral arterial disease – a proof of concept study	2019
Eoin Moloney Joanne O'Connor Professor Dawn Craig Shannon Robalino Alexandros Chrysos et al.	Systematic Review of Economic Models Used to Compare Techniques for Detecting Peripheral Arterial Disease	2019
Raksheeth Agarwal Dr John O'Sullivan Professor John Allen Dr Louise Coats	Tissue oxygen saturation assessment of microvascular perfusion in adults with Fontan palliation and comparator groups using vascular optical spectrophotometry – A pilot study	2019
Dr Yemi Oluboyede Professor Laura Ternent Professor Luke Vale Professor John Allen	Using a Discrete-Choice Experiment to Estimate the Preferences of Clinical Practitioners for a Novel Non-invasive Device for Diagnosis of Peripheral Arterial Disease in Primary Care	2019
Professor John Allen Dr Bridget Griffiths Audrey Macdonald	A Multicenter Study of the Validity and Reliability of Responses to Hand Cold Challenge as Measured by Laser Speckle Contrast Imaging and Thermography	2018
Professor Gerard Stansby Professor John Allen	Innovative multi-site photoplethysmography analysis for quantifying pulse amplitude and timing variability characteristics in peripheral arterial disease	2018
Costanzo Di Maria Dr Annette Klinge Emeritus Professor Alan Murray Dr Dingchang Zheng Dr John O'Sullivan et al.	Innovative multi-site photoplethysmography measurement and analysis demonstrating increased arterial stiffness in paediatric heart transplant recipients	2018
Professor John Allen	Nailfold capillaroscopy - how many fingers should be examined to detect abnormality?	2018
Professor John Allen Costanzo Di Maria Dr Sam Urwin Emeritus Professor Alan Murray Dr Lesley Ottewell et al.	Novel optical assessments of tissue composition and viability using fluorescence spectroscopy and tissue oxygenation spectrophotometry in patients with systemic sclerosis - a pilot study	2018
Dr Bill Waugh Professor John Allen Dr Andrew Sims Dr Thomas Beale	Novel Signal Noise Reduction Method through Cluster Analysis, Applied to Photoplethysmography	2018
Audrey Macdonald Professor John Allen	Reliability of a novel thermal imaging system for temperature assessment of healthy feet.	2018
Professor John Allen Professor Gerard Stansby Jan Lecouturier Dr Scott Wilkes Professor Luke Vale et al.	Successful development of a multi-site photoplethysmography device for fast peripheral arterial disease diagnosis in primary care	2018
Professor John Allen	The assessment of nailfold capillaries: comparison of dermoscopy and nailfold videocapillaroscopy	2018
Professor John Allen Audrey Macdonald	A medical thermal imaging device for the prevention of diabetic foot ulceration	2017
Professor Gerard Stansby Professor John Allen	Confirmed utility of tissue oxygen saturation assessments for predicting healing capability in below knee amputation	2017
Professor John Allen	Development of a Clinical Microvascular Imaging and Vascular Optics Facility: The Newcastle Upon Tyne (UK) Experience	2017
Professor John Allen Dr Thomas Beale	Device for use in the assessment of Peripheral Arterial Disease	2017
Dr Daniel Kyle Professor John Allen Professor Gerard Stansby	Exploratory Thermal Imaging Assessments of the Feet in Patients with Lower Limb Peripheral Arterial Disease	2017
Professor John Allen	Intra-and inter-observer reliability of nailfold videocapillaroscopy - A possible outcome measure for systemic sclerosis-related microangiopathy	2017
Costanzo Di Maria Professor John Allen	Intraoperative Thermal and Laser Speckle Contrast Imaging Assessment of Bowel Perfusion in Two Cases of Colorectal Resection Surgery	2017
Dr Bridget Griffiths Professor John Allen	Quantification of differences between nailfold capillaroscopy images with a scleroderma pattern and normal pattern using measures of geometric and algorithmic complexity	2017
Audrey Macdonald Professor John Allen	Reproducibility of Thermal Images: Some Healthy Examples.	2017
Audrey Macdonald Professor John Allen	Thermal symmetry of healthy feet: a precursor to a thermal study of diabetic feet prior to skin breakdown	2017
Professor John Allen	Towards a consensus on the understanding and analysis of the pulse waveform: Results from the 2016 Workshop on Arterial Hemodynamics: Past, present and future	2017
Professor John Allen	Infrared thermometry reveals no differences of the skin temperatures at the plantar, dorsal, medial and lateral sites between the right foot and left foot in healthy volunteers	2016
Dr Alan Bagnall Professor John Allen Dr Hannah Sinclair Professor Vijay Kunadian	Endothelial Dysfunction and Coronary Artery Disease: A State of the Art Review	2015
Costanzo Di Maria Dr Petros Perros Professor John Allen	Exploratory thermal and laser speckle contrast imaging measurements of eye inflammation in a case of thyroid eye disease	2015
Professor John Allen	Illuminating light in medical diagnostics and treatment	2015
Professor John Allen Costanzo Di Maria Dr Ian Forrest	Imaging assessments of patients with suspected systemic sclerosis and associated inflammatory lung disease	2015
Dr Scott Wilkes Professor Gerard Stansby Dr Andrew Sims Professor John Allen	Peripheral Arterial Disease: diagnostic challenges and how photoplethysmography may help	2015
Costanzo Di Maria Professor John Allen	Quantifying the correlation between photoplethysmography and laser Doppler flowmetry microvascular low-frequency oscillations	2015
Professor John Allen	Reliability and Validity of Mean Vessel Width in Capillaroscopy for Evaluating Systemic Sclerosis-Related Microangiopathy	2015
Professor John Allen David Talbot	Thermal imaging and its potential for artery-venous fistula function assessment	2015
Professor John Allen Dr Nicola Leech	Thermal imaging potential for assessing diabetic Charcot foot syndrome	2015
Professor John Allen Professor Grainne Gorman	Thermographic assessment of the presence of fatty tumours in myoclonic epilepsy with ragged red fibres	2015
Professor John Allen Dr Michael Drinnan	A pilot study of new spectrophotometry device to measure tissue oxygen saturation	2014
Professor John Allen	Microvascular imaging: techniques and opportunities for clinical physiological measurements	2014
Dr Neil McKay Dr Bridget Griffiths Costanzo Di Maria Stephen Hedley Emeritus Professor Alan Murray et al.	Novel photoplethysmography cardiovascular assessments in patients with Raynaud's phenomenon and systemic sclerosis: a pilot study	2014
Costanzo Di Maria Professor John Allen Christopher Neoh Dr Petros Perros	Novel Thermal Imaging Analysis Technique for Detecting Inflammation in Thyroid Eye Disease	2014
Professor John Allen	Reliability of Nailfold Capillary Density Measurement As a Possible Outcome Measure for Systemic Sclerosis-Related Microangiopathy	2014
Dr Rachel Green Professor John Allen	Role of medical thermography in treatment of Frey's syndrome with botulinum toxin A	2014
Professor John Allen	Subject Preparation and Thermal Acclimatization Prior to Mild Cold Challenge Testing Using Dynamic Thermal Imaging	2014
Costanzo Di Maria Dr Annette Klinge Dr Dingchang Zheng Emeritus Professor Alan Murray Dr John O'Sullivan et al.	A pilot study of photoplethysmographic peripheral pulse transit times in paediatric heart transplant recipients and healthy children	2013
Professor John Allen	Beyond the ankle brachial pressure index for the diagnosis of peripheral arterial disease – time for a new look at photoplethysmography?	2013
Professor John Allen	Evaluation of three thermal imaging cameras for skin temperature measurement using a blackbody reference source and a spatial resolution test object	2013
Professor John Allen	Finger microvascular responses to deep inspiratory gasp assessed and quantified using wavelet analysis	2013
Dr Kirstie Anderson Professor John Allen	Novel assessment of microvascular changes in idiopathic restless legs syndrome (Willis-Ekbom disease)	2013
Professor John Allen Emeritus Professor Alan Murray Costanzo Di Maria Emerita Professor Julia Newton	Chronic fatigue syndrome and impaired peripheral pulse characteristics on orthostasis-a new potential diagnostic biomarker	2012
Costanzo Di Maria Dr Annette Klinge Dr Ding Chang Zheng Emeritus Professor Alan Murray Dr John O'Sullivan et al.	Feasibility of monitoring vascular ageing by multi-site photoplethysmography	2012
Dr Sharad Agarwal Professor John Allen Emeritus Professor Alan Murray	Laser Doppler assessment of dermal circulatory changes in people with coronary artery disease	2012
Dr Philip Langley Costanzo Di Maria Wenfeng Duan Marjan Bojarnejad Dr Ding Chang Zheng et al.	An algorithm for assessment of quality of ECGs acquired via mobile telephones	2011
Professor John Allen	New conceptual and mathematical forms for the contour of volume wave of arterial pulse	2011
Professor John Allen	Capillaroscopy in healthy subjects of different ages	2010
Professor John Allen Emeritus Professor Alan Murray	Comparative reproducibility of dermal microvascular blood flow changes in response to acetylcholine iontophoresis, hyperthermia and reactive hyperaemia	2010
Dr Annette Klinge Professor John Allen Emeritus Professor Alan Murray Dr John O'Sullivan	Increased pulse wave velocity and blood pressure in children who have undergone cardiac transplantation.	2009
Sam Stevens Professor John Allen Emeritus Professor Alan Murray Professor David Jones Emerita Professor Julia Newton et al.	Microvascular optical assessment confirms the presence of peripheral autonomic dysfunction in primary biliary cirrhosis	2009
Dr Philip Langley Susan King Dr Ding Chang Zheng Emma Bowers Professor John Allen et al.	Predicting acute hypotensive episodes from mean arterial pressure	2009
Professor John Allen Klaus Overbeck Alex Nath Emeritus Professor Alan Murray Professor Gerard Stansby et al.	A prospective comparison of bilateral photoplethysmography versus the ankle-brachial pressure index for detecting and quantifying lower limb peripheral arterial disease	2008
Dr Ding Chang Zheng Professor John Allen Emeritus Professor Alan Murray	Determination of aortic valve opening time and left ventricular peak filling rate from the peripheral pulse amplitude in patients with ectopic beats	2008
Susan King Abigail Haigh Dr Annette Klinge Dr Ding Chang Zheng Sam Stevens et al.	Body Surface Potential Mapping for Detection of Myocardial Infarct Sites	2007
Dr Dingchang Zheng Professor John Allen Emeritus Professor Alan Murray	Non-invasive in vivo assessment of changes in peripheral arterial properties with estimation of arterial volume compliance	2007
Professor John Allen	Photoplethysmography and its application in clinical physiological measurement	2007
Professor John Allen Elizabeth Kokkinos Emeritus Professor Alan Murray Emeritus Professor Brian Diffey Dr Simon Meggitt et al.	Assessment of skin fluorescence characteristics in systemic sclerosis	2006
Dr Dingchang Zheng Professor John Allen Emeritus Professor Alan Murray	Development of a method for determining arterial pulse propagation times and influence of arterial compliance	2006
Professor John Allen Dr Alan Murray	Impaired systemic microvascular endothelial function with coronary artery disease can be detected nowinvasively using novel laser doppler techniques	2006
Professor John Allen Klaus Overbeck Professor Gerard Stansby Emeritus Professor Alan Murray	Photoplethysmography assessments in cardiovascular disease	2006
Professor Namita Kumar Dr Bridget Griffiths Professor John Allen	Thermographic and symptomatic effect of a single dose of sildenafil citrate on Raynaud's phenomenon in patients with systemic sclerosis: A potential treatment	2006
Professor John Allen Crispian Oates Dr Ahmed Chishti David Talbot Emeritus Professor Alan Murray et al.	Thermography and colour duplex ultrasound assessments of arterio-venous fistula function in renal patients	2006
Professor John Allen David Talbot Dr Alan Murray	Automated infrared image processing for the assessment of arterio-venous fistula function in renal patients	2005
Dr Louise Allan Dr Simon Kerr Dr Clive Ballard Professor John Allen Emeritus Professor Alan Murray et al.	Autonomic function assessed by heart rate variability is normal in Alzheimer's disease and vascular dementia	2005
Dr Louise Allan Dr Nick Steen Professor John Allen Emeritus Professor Alan Murray Professor Rose Anne Kenny et al.	Autonomic function is impaired in elderly stroke survivors	2005
Dr Dingchang Zheng Professor John Allen Emeritus Professor Alan Murray	Effect of external cuff pressure on arterial compliance	2005
Professor John Allen Crispian Oates Tim Lees Emeritus Professor Alan Murray	Photoplethysmography detection of lower limb peripheral arterial occlusive disease: a comparison of pulse timing, amplitude and shape characteristics	2005
Professor John Allen Crispian Oates Dr Ahmed Chishti David Talbot Emeritus Professor Alan Murray et al.	Renal fistula assessment using automated thermal imaging	2005
Professor John Allen Karen Walker Dr Bridget Griffiths Emeritus Professor Alan Murray	Skin temperature and objective colour measurements in patients with Raynaud’s phenomenon secondary to connective tissue disease	2005
Dr Fiona Smith Abigail Haigh Joanne Wild Emma Bowers Professor John Allen et al.	Study of the causes of blood pressure variability during manual sphygmomanometer measurement	2005
Dr Philip Langley Professor John Allen Emma Bowers Dr Michael Drinnan Abigail Haigh et al.	The ebb and flow of heart rate variability: Simulation of 24 hour heart rate time series using time series data from naturally occurring phenomena	2005
Dr Nitin Kumar Professor John Allen Emeritus Professor Alan Murray Dr Bridget Griffiths	A pilot study assessing the response of single dose sildenafil citrate (Viagra) in the treatment of Raynaud’s phenomenon in patients with systemic sclerosis	2004
Dr Philip Langley Professor John Allen Emma Bowers Dr Michael Drinnan Susan King et al.	Analysis of RR Interval and Fibrillation Frequency and Amplitude for Predicting Spontaneous Termination of Atrial Fibrillation.	2004
Professor John Allen Dr John O'Sullivan Susan King Emeritus Professor Alan Murray	Characterization of the Korotkoff sounds using joint time-frequency analysis	2004
Professor John Allen Emeritus Professor Alan Murray	Age-related changes in multi-site photoplethysmographic peripheral pulse shape characteristics at various body sites	2003
Professor John Allen Emeritus Professor Alan Murray	Age-related changes in the characteristics of the photoplethysmographic pulse shape at various body sites	2003
Dr Philip Langley Emma Bowers Dr Michael Drinnan Professor John Allen Dr Andrew Sims et al.	An algorithm to distinguish ischaemic and non-ischaemic ST changes in the Holter ECG	2003
Dr Philip Langley Emma Bowers Nicola Brown Dr Michael Drinnan Professor John Allen et al.	An algorithm to distinguish ischemic and non-ischaemic ST changes in the Holter ECG	2003
Dr Andrew McLaren Professor John Allen Emeritus Professor Alan Murray Dr Clive Ballard Professor Rose Anne Kenny et al.	Cardiovascular effects of donepezil in patients with dementia	2003
Professor John Allen Emeritus Professor Alan Murray	Dynamic characteristics of the peripheral pulse: an investigation into the differences between right and left body sites	2003
Dr Louise Allan Dr Andrew McLaren Professor John Allen Dr Clive Ballard Professor Ian McKeith et al.	Heart rate variability is reduced in dementia with Lewy bodies but not Alzheimer’s disease or vascular dementia.	2003
Professor John Allen Susan King	Time and frequency analysis of the Korotkoff sounds	2003
Professor John Allen	[PhD Thesis] The measurement and analysis of multi-site photoplethysmographic pulse waveforms in health and arterial disease	2002
Professor John Allen Emeritus Professor Alan Murray	Age-related changes in peripheral pulse timing characteristics at the ears, fingers and toes	2002
Emeritus Professor Alan Murray Dr Philip Langley Dr Fiona Smith Professor John Allen Dr Clive Griffiths et al.	Contributions of cardiovascular physics and engineering to the solution of clinical problems	2002
Dr Fiona Smith Emma Bowers Dr Philip Langley Professor John Allen Emeritus Professor Alan Murray et al.	Heart rate variability characteristics required for simulation of interval sequences	2002
Professor John Allen Emeritus Professor Alan Murray	Microvascular blood flow and skin temperature changes in the fingers following a deep inspiratory gasp	2002
Professor John Allen Emeritus Professor Alan Murray	Photoplethysmography - a tool for assessing the microcirculation.	2002
Abishek Umashankar Dr Philip Langley Dr Michael Drinnan Professor John Allen Dr Fiona Smith et al.	Simulation of cardiac interval time series	2002
Dr John O'Sullivan Professor John Allen Emeritus Professor Alan Murray	The forgotten Korotkoff phases: How often are phases II and III present, and how do they relate to the other Korotkoff phases?	2002
Dr John O'Sullivan Professor John Allen Emeritus Professor Alan Murray	A clinical study of the Korotkoff phases of blood pressure in children	2001
Dr Philip Langley Professor John Allen Abishek Umashankar Dr Fiona Smith Emeritus Professor Alan Murray et al.	Can paroxysmal atrial fibrillation be predicted?	2001
Professor John Allen Emeritus Professor Alan Murray	Multi-site photoplethysmographic peripheral pulse measurement and shape analysis	2001
Dr Michael Drinnan Professor John Allen Emeritus Professor Alan Murray	Relation between heart rate and pulse transit time during paced respiration	2001
Professor John Allen Emeritus Professor Alan Murray	Comparison of regional variability in multi-site photoplethysmographic pulse wave characteristics	2000
Dr Michael Drinnan Professor John Allen Dr Philip Langley Emeritus Professor Alan Murray	Detection of sleep apnoea from frequency analysis of heart rate variability	2000
Professor John Allen Emeritus Professor Alan Murray	Similarity in bilateral photoplethysmographic peripheral pulse wave characteristics at the ears, thumbs and toes	2000
Professor John Allen Dr Alan Murray	Variability of photoplethysmography peripheral pulse measurements at the ears, thumbs and toes	2000
Professor John Allen Emeritus Professor Alan Murray	Modelling the relationship between peripheral blood pressure and blood volume pulses using linear and neural network system identification techniques	1999
Professor John Allen Emeritus Professor Alan Murray	Multi-site photoplethysmographic peripheral pulse measurement and correlation analysis	1999
Professor John Allen Emeritus Professor Alan Murray	Skin temperature and photoelectric plethysmography recovery characteristics during mild cold challenge testing in normal subjects	1999
Professor John Allen Emeritus Professor Alan Murray	Skin temperature and photoplethysmography recovery characteristics during mild cold challenge testing in normal subjects	1999
Professor John Allen Emeritus Professor Alan Murray	Assessing ECG signal quality on a coronary care unit	1996
Professor John Allen Emeritus Professor Alan Murray	Comparison of lower limb arterial assessments using color-duplex ultrasound and ankle/brachial pressure index measurements.	1996
Professor John Allen Emeritus Professor Alan Murray	Prospective assessment of an artificial neural network for the detection of peripheral vascular disease from lower limb pulse waveforms	1995
Emeritus Professor Alan Murray Professor John Allen	Simplified body-surface electrocardiographic maps with depolarization magnitude and direction	1994