Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

[1]  Walter Karlen,et al.  Design challenges for camera oximetry on a mobile phone , 2012, 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[2]  W Lu,et al.  Research on the main elements influencing blood pressure measurement by pulse wave velocity. , 1992, Frontiers of medical and biological engineering : the international journal of the Japan Society of Medical Electronics and Biological Engineering.

[3]  E. O’Brien,et al.  The British Hypertension Society protocol for the evaluation of automated and semi-automated blood pressure measuring devices with special reference to ambulatory systems. , 1990, Journal of hypertension.

[4]  B. Morgenstern,et al.  Human blood pressure determination by sphygmomanometry. , 1993, Circulation.

[5]  A. C. M. Dassel,et al.  Reflectance pulse oximetry at the forehead improves by pressure on the probe , 1995, Journal of Clinical Monitoring.

[6]  SeongHwan Cho,et al.  A pulse transit time measurement method based on electrocardiography and bioimpedance , 2009, 2009 IEEE Biomedical Circuits and Systems Conference.

[7]  W.-C. Yu,et al.  Determinants of pressure wave reflection: characterization by the transit time-independent reflected wave amplitude , 2010, Journal of Human Hypertension.

[8]  D. Bergel,et al.  The dynamic elastic properties of the arterial wall , 1961, The Journal of physiology.

[9]  Roger G. Mark,et al.  An open-source algorithm to detect onset of arterial blood pressure pulses , 2003, Computers in Cardiology, 2003.

[10]  J. Jossinet,et al.  Impedance plethysmography for the evaluation of pulse-wave velocity in limbs , 2006, Medical and Biological Engineering and Computing.

[11]  M. Masè,et al.  Feasibility of cuff-free measurement of systolic and diastolic arterial blood pressure. , 2011, Journal of electrocardiology.

[12]  M. O'Rourke,et al.  Mechanical factors in arterial aging: a clinical perspective. , 2007, Journal of the American College of Cardiology.

[13]  Hidehiro Hosaka,et al.  The Relationship Between Modified Pulse Wave Transit Time and Cardiovascular Changes in Isoflurane Anesthetized Dogs , 1999, Journal of Clinical Monitoring and Computing.

[14]  M. Cohen,et al.  Vascular contraction: effect of age and extracellular calcium. , 1976, Blood vessels.

[15]  R. G. Mark,et al.  Reduction of false arterial blood pressure alarms using signal quality assessement and relationships between the electrocardiogram and arterial blood pressure , 2004, Medical and Biological Engineering and Computing.

[16]  L. A. Geddes,et al.  Pulse arrival time as a method of obtaining systolic and diastolic blood pressure indirectly , 1981, Medical and Biological Engineering and Computing.

[17]  Qiao Zhang,et al.  Noninvasive cuffless blood pressure estimation using pulse transit time and Hilbert-Huang transform , 2013, Comput. Electr. Eng..

[18]  James McNames,et al.  An automatic beat detection algorithm for pressure signals , 2005, IEEE Transactions on Biomedical Engineering.

[19]  C. Douniama,et al.  Blood pressure tracking capabilities of pulse transit times in different arterial segments: A clinical evaluation , 2009, 2009 36th Annual Computers in Cardiology Conference (CinC).

[20]  I. Starr,et al.  STUDIES ON THE ESTIMATION OF CARDIAC OUPTUT IN MAN, AND OF ABNORMALITIES IN CARDIAC FUNCTION, FROM THE HEART'S RECOIL AND THE BLOOD'S IMPACTS; THE BALLISTOCARDIOGRAM , 1939 .

[21]  A. R. Lind,et al.  Aging, isometric strength and endurance, and cardiovascular responses to static effort. , 1975, Journal of applied physiology.

[22]  R. Stout,et al.  The Effect of Venous Pulsation on the Forehead Pulse Oximeter Wave Form as a Possible Source of Error in Spo2 Calculation , 2005, Anesthesia and analgesia.

[23]  G. Langewouters,et al.  The static elastic properties of 45 human thoracic and 20 abdominal aortas in vitro and the parameters of a new model. , 1984, Journal of biomechanics.

[24]  R. Anderson,et al.  The optics of human skin. , 1981, The Journal of investigative dermatology.

[25]  Toshiyo Tamura,et al.  Relationship Between Measurement Site and Motion Artifacts in Wearable Reflected Photoplethysmography , 2011, Journal of Medical Systems.

[26]  R. Patterson,et al.  Fundamentals of impedance cardiography , 1989, IEEE Engineering in Medicine and Biology Magazine.

[27]  Shinobu Tanaka,et al.  Comparison between red, green and blue light reflection photoplethysmography for heart rate monitoring during motion , 2013, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC).

[28]  Marc Garbey,et al.  Imaging the cardiovascular pulse , 2005, 2005 IEEE Computer Society Conference on Computer Vision and Pattern Recognition (CVPR'05).

[29]  Claudio Sartori,et al.  Noninvasive and Nonocclusive Blood Pressure Estimation Via a Chest Sensor , 2013, IEEE Transactions on Biomedical Engineering.

[30]  Amir Haghighat,et al.  Snapshots of Hemodynamics: An Aid for Clinical Research and Graduate Education , 2005 .

[31]  J. Timisjärvi,et al.  Electromechanical delay in the intact dog heart. , 1985, International journal of cardiology.

[32]  D. Altman,et al.  Applying the right statistics: analyses of measurement studies , 2003, Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.

[33]  Y.T. Zhang,et al.  A Novel Calibration Method for Noninvasive Blood Pressure Measurement Using Pulse Transit Time , 2007, 2007 4th IEEE/EMBS International Summer School and Symposium on Medical Devices and Biosensors.

[34]  Guanqun Zhang,et al.  Pulse arrival time is not an adequate surrogate for pulse transit time as a marker of blood pressure. , 2011, Journal of applied physiology.

[35]  M. G. Taylor,et al.  Alterations with Age in the Viscoelastic Properties of Human Arterial Walls , 1966, Circulation research.

[36]  X. Teng,et al.  The effect of applied sensor contact force on pulse transit time , 2006, Physiological measurement.

[37]  G. V. Marie,et al.  The relationship between arterial blood pressure and pulse transit time during dynamic and static exercise. , 1984, Psychophysiology.

[38]  Marc Garbey,et al.  Contact-Free Measurement of Cardiac Pulse Based on the Analysis of Thermal Imagery , 2007, IEEE Transactions on Biomedical Engineering.

[39]  I. C. Benson,et al.  STUDIES ON THE ELASTIC PROPERTIES OF HUMAN ISOLATED AORTA. , 1937, The Journal of clinical investigation.

[40]  B. Brodie,et al.  Beta‐Receptor Activity in Aorta: Variations with Age and Species , 1970, Circulation research.

[41]  R. Patterson,et al.  IMPEDANCE CARDIOGRAPHY AS A NONINVASIVE METHOD OF MONITORING CARDIAC FUNCTION AND OTHER PARAMETERS OF THE CARDIOVASCULAR SYSTEM * , 1970 .

[42]  Patrick Segers,et al.  The change in arterial stiffness over the cardiac cycle rather than diastolic stiffness is independently associated with left ventricular mass index in healthy middle-aged individuals , 2012, Journal of hypertension.

[43]  Nima Fazeli,et al.  Data-driven lossy tube-load modeling of arterial tree: in-human study. , 2014, Journal of biomechanical engineering.

[44]  W. Cui,et al.  In vivo reflectance of blood and tissue as a function of light wavelength , 1990, IEEE Transactions on Biomedical Engineering.

[45]  N Westerhof,et al.  Measurement of pulse wave velocity using a beat-sampling technique. , 1989, Annals of biomedical engineering.

[46]  Alan Mathewson,et al.  An Investigation of Pulse Transit Time as a Non-Invasive Blood Pressure Measurement Method , 2011 .

[47]  Daniel Burkhoff,et al.  Evaluation of a noninvasive continuous cardiac output monitoring system based on thoracic bioreactance. , 2007, American journal of physiology. Heart and circulatory physiology.

[48]  Michel Remoissenet,et al.  Waves called solitons , 1994 .

[49]  James H. Currens,et al.  A comparison of the blood pressure in the lying and standing positions: A study of five hundred men and five hundred women , 1948 .

[50]  J. Fahrenberg,et al.  Methodological guidelines for impedance cardiography. , 1990, Psychophysiology.

[51]  K Sagawa,et al.  Effect of Nitroglycerin on Aortic Impedance, Diameter, and Pulse‐Wave Velocity , 1986, Circulation research.

[52]  R. Armentano,et al.  Arterial wall mechanics in conscious dogs. Assessment of viscous, inertial, and elastic moduli to characterize aortic wall behavior. , 1995, Circulation research.

[53]  N.V. Thakor,et al.  Applications of adaptive filtering to ECG analysis: noise cancellation and arrhythmia detection , 1991, IEEE Transactions on Biomedical Engineering.

[54]  J McLaughlin,et al.  Piezoelectric sensor determination of arterial pulse wave velocity. , 2003, Physiological measurement.

[55]  Masaki Shuzo,et al.  Continuous Blood Pressure Monitoring in Daily Life , 2010 .

[56]  L. Wurfel Mcdonald S Blood Flow In Arteries Theoretical Experimental And Clinical Principles , 2016 .

[57]  Omer T. Inan,et al.  A Novel System Identification Technique for Improved Wearable Hemodynamics Assessment , 2015, IEEE Transactions on Biomedical Engineering.

[58]  M. Nitzan,et al.  The difference in pulse transit time to the toe and finger measured by photoplethysmography. , 2002, Physiological measurement.

[59]  Vijay Kumar,et al.  Towards continuous monitoring of pulse rate in neonatal intensive care unit with a webcam , 2014, 2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[60]  A. Morice,et al.  Cardiac and respiratory related electrical impedance changes in the human thorax , 1994, IEEE Transactions on Biomedical Engineering.

[61]  Westgate Road,et al.  Photoplethysmography and its application in clinical physiological measurement , 2007 .

[62]  Luciano Bernardi,et al.  Slow Breathing Improves Arterial Baroreflex Sensitivity and Decreases Blood Pressure in Essential Hypertension , 2005, Hypertension.

[63]  Carmen C. Y. Poon,et al.  An Armband Wearable Device for Overnight and Cuff-Less Blood Pressure Measurement , 2014, IEEE Transactions on Biomedical Engineering.

[64]  Willis J. Tompkins,et al.  A Real-Time QRS Detection Algorithm , 1985, IEEE Transactions on Biomedical Engineering.

[65]  A. Bank,et al.  Contribution of collagen, elastin, and smooth muscle to in vivo human brachial artery wall stress and elastic modulus. , 1996, Circulation.

[66]  Xiufeng Yang,et al.  Noninvasive monitoring of blood pressure using optical Ballistocardiography and Photoplethysmograph approaches , 2013, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC).

[67]  R. Patterson,et al.  Studies on the effect of controlled volume change on the thoracic electrical impedance , 1978, Medical and Biological Engineering and Computing.

[68]  Nima Fazeli,et al.  Comparative study on tube-load modeling of arterial hemodynamics in humans. , 2013, Journal of biomechanical engineering.

[69]  H. Asada,et al.  Utility of the Photoplethysmogram in Circulatory Monitoring , 2008, Anesthesiology.

[70]  Chandra S. Bomma Exercise and the Heart, 5th Edition , 2006 .

[71]  S S Franklin,et al.  Predominance of Isolated Systolic Hypertension Among Middle-Aged and Elderly US Hypertensives: Analysis Based on National Health and Nutrition Examination Survey (NHANES) III , 2001, Hypertension.

[72]  Daniel McDuff,et al.  Advancements in Noncontact, Multiparameter Physiological Measurements Using a Webcam , 2011, IEEE Transactions on Biomedical Engineering.

[73]  P. C. Pandey,et al.  Automatic detection of characteristic points in impedance cardiogram , 2011, 2011 Computing in Cardiology.

[74]  Carmen C. Y. Poon,et al.  Attenuation of Systolic Blood Pressure and Pulse Transit Time Hysteresis During Exercise and Recovery in Cardiovascular Patients , 2014, IEEE Transactions on Biomedical Engineering.

[75]  Jeffrey Wood,et al.  Using Individualized Pulse Transit Time Calibration to Monitor Blood Pressure During Exercise , 2013, ICIMTH.

[76]  C. Douniama,et al.  Acquisition of Parameters for Noninvasive Continuous Blood Pressure Estimation – Review of the Literature and Clinical Trial , 2009 .

[77]  J Licinio,et al.  Cardiovascular and neuroendocrine adjustment to public speaking and mental arithmetic stressors. , 1997, Psychophysiology.

[78]  Huey-Ru Chuang,et al.  Measurement of heart and breathing signals of human subjects through barriers with microwave life-detection systems , 1988, Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[79]  Toshiyo Tamura,et al.  Wearable Photoplethysmographic Sensors—Past and Present , 2014 .

[80]  Leslie A Saxon Ubiquitous Wireless ECG Recording: A Powerful Tool Physicians Should Embrace , 2013, Journal of cardiovascular electrophysiology.

[81]  Yan Chen,et al.  Continuous and Noninvasive Blood Pressure Measurement: A Novel Modeling Methodology of the Relationship Between Blood Pressure and Pulse Wave Velocity , 2009, Annals of Biomedical Engineering.

[82]  Myoungho Lee,et al.  Adaptive threshold method for the peak detection of photoplethysmographic waveform , 2009, Comput. Biol. Medicine.

[83]  Daniel Levy,et al.  Arterial and cardiac aging: major shareholders in cardiovascular disease enterprises: Part I: aging arteries: a "set up" for vascular disease. , 2003, Circulation.

[84]  J. J. Settels,et al.  Physiocal, calibrating finger vascular physiology for finapres , 1995 .

[85]  Gregory T. A. Kovacs,et al.  Rapid Assessment of Cardiac Contractility on a Home Bathroom Scale , 2011, IEEE Transactions on Information Technology in Biomedicine.

[86]  Roozbeh Jafari,et al.  BioWatch — A wrist watch based signal acquisition system for physiological signals including blood pressure , 2014, 2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[87]  Kejia Li,et al.  A Wireless Reflectance Pulse Oximeter With Digital Baseline Control for Unfiltered Photoplethysmograms , 2012, IEEE Transactions on Biomedical Circuits and Systems.

[88]  Kouhyar Tavakolian,et al.  Ballistocardiography and Seismocardiography: A Review of Recent Advances , 2015, IEEE Journal of Biomedical and Health Informatics.

[89]  J. D. Bourland,et al.  Measurement of pulse-wave velocity using a beat-sampling technique , 2006, Annals of Biomedical Engineering.

[90]  Janis Spigulis,et al.  Simultaneous recording of skin blood pulsations at different vascular depths by multiwavelength photoplethysmography. , 2007, Applied optics.

[91]  K. Ashoka Reddy,et al.  Use of Fourier Series Analysis for Motion Artifact Reduction and Data Compression of Photoplethysmographic Signals , 2009, IEEE Transactions on Instrumentation and Measurement.

[92]  R H Guy,et al.  Basal perfusion of the cutaneous microcirculation: measurements as a function of anatomic position. , 1983, The Journal of investigative dermatology.

[93]  H Harry Asada,et al.  Mobile monitoring with wearable photoplethysmographic biosensors. , 2003, IEEE engineering in medicine and biology magazine : the quarterly magazine of the Engineering in Medicine & Biology Society.

[94]  J Liu,et al.  Large artery remodeling during aging: biaxial passive and active stiffness. , 1998, Hypertension.

[95]  Gi-Ryon Kim,et al.  Estimation of Systolic and Diastolic Pressure using the Pulse Transit Time , 2010 .

[96]  Voicu Groza,et al.  Coefficient-Free Blood Pressure Estimation Based on Pulse Transit Time–Cuff Pressure Dependence , 2013, IEEE Transactions on Biomedical Engineering.

[97]  Massimo Lombardi,et al.  Robust estimation of pulse wave transit time using group delay , 2014, Journal of magnetic resonance imaging : JMRI.

[98]  C. Ahlstrom,et al.  Noninvasive investigation of blood pressure changes using the pulse wave transit time: a novel approach in the monitoring of hemodialysis patients , 2005, Journal of Artificial Organs.

[99]  R. D. Harkness,et al.  The collagen and elastin content of the arterial wall in the dog , 1957, Proceedings of the Royal Society of London. Series B - Biological Sciences.

[100]  Rafi Ahamed Shaik,et al.  Cancellation of artifacts in ECG signals using block adaptive filtering techniques. , 2011, Advances in experimental medicine and biology.

[101]  Jin-Oh Hahn,et al.  Estimation of pulse transit time using two diametric blood pressure waveform measurements. , 2010, Medical engineering & physics.

[102]  J. T. Shepherd,et al.  Circulatory effects of stimulating the carotid arterial stretch receptors in man at rest and during exercise. , 1966, The Journal of clinical investigation.

[103]  John G. Webster,et al.  Design of Pulse Oximeters , 1997 .

[104]  A Steptoe,et al.  Pulse wave velocity and blood pressure change: calibration and applications. , 1976, Psychophysiology.

[105]  O. Zaderykhin,et al.  Adaptive algorithm for continuous monitoring of blood pressure using a pulse transit time , 2013, 2013 IEEE XXXIII International Scientific Conference Electronics and Nanotechnology (ELNANO).

[106]  Survi Kyal,et al.  Constrained independent component analysis approach to nonobtrusive pulse rate measurements. , 2012, Journal of biomedical optics.

[107]  A Murray,et al.  Age-related changes in peripheral pulse timing characteristics at the ears, fingers and toes , 2002, Journal of Human Hypertension.

[108]  Hirofumi Tanaka,et al.  Carotid-Femoral Pulse Wave Velocity: Impact of Different Arterial Path Length Measurements. , 2009, Artery research.

[109]  J. Carroll,et al.  Determination of pulse wave velocities with computerized algorithms. , 1991, American heart journal.

[110]  Ko Keun Kim,et al.  A Smart Health Monitoring Chair for Nonintrusive Measurement of Biological Signals , 2012, IEEE Transactions on Information Technology in Biomedicine.

[111]  A Mathewson,et al.  An examination of calibration intervals required for accurately tracking blood pressure using pulse transit time algorithms , 2013, Journal of Human Hypertension.

[112]  E. F. Greneker,et al.  Radar sensing of heartbeat and respiration at a distance with applications of the technology , 1997 .

[113]  T. Yambe,et al.  A Great Impact of Green Video Signals on Tele-Healthcare in Daily Life, Especially for Rural or Disaster Areas , 2013 .

[114]  A. C. Burton Relation of structure to function of the tissues of the wall of blood vessels. , 1954, Physiological reviews.

[115]  D. McAuley,et al.  Accuracy and precision of blood pressure determination with the Finapres: an overview using re-sampling statistics , 1998, Journal of Human Hypertension.

[116]  Heather T. Ma,et al.  A Blood Pressure Monitoring Method for Stroke Management , 2014, BioMed research international.

[117]  S. Hansen,et al.  Oscillometric blood pressure measurement used for calibration of the arterial tonometry method contributes significantly to error , 2006, European journal of anaesthesiology.

[118]  Carmen C. Y. Poon,et al.  Unobtrusive Sensing and Wearable Devices for Health Informatics , 2014, IEEE Transactions on Biomedical Engineering.

[119]  G. Drzewiecki,et al.  Theory of the oscillometric maximum and the systolic and diastolic detection ratios , 2006, Annals of Biomedical Engineering.

[120]  Steffen Leonhardt,et al.  Adaptive Beat-to-Beat Heart Rate Estimation in Ballistocardiograms , 2011, IEEE Transactions on Information Technology in Biomedicine.

[121]  Roman Cmejla,et al.  Parameters for mean blood pressure estimation based on electrocardiography and photoplethysmography , 2011, 2011 International Conference on Applied Electronics.

[122]  G. Parati,et al.  Comparison of Finger and Intra‐arterial Blood Pressure Monitoring at Rest and During Laboratory Testing , 1989, Hypertension.

[123]  Benjamin C. K. Tee,et al.  Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring , 2013, Nature Communications.

[124]  George E. Brown,et al.  The cold pressor test for measuring the reactibility of the blood pressure: Data concerning 571 normal and hypertensive subjects , 1936 .

[125]  G Mancia,et al.  Circulatory reflexes from carotid and extracarotid baroreceptor areas in man. , 1977, Circulation research.

[126]  B. Alpert,et al.  Oscillometric blood pressure: a review for clinicians. , 2014, Journal of the American Society of Hypertension : JASH.

[127]  D Shapiro,et al.  Pulse transit time and blood pressure: an intensive analysis. , 1983, Psychophysiology.

[128]  J. Jalonen,et al.  Static-charge-sensitive bed ballistocardiography in cardiovascular monitoring. , 1996, Clinical physiology.

[129]  Ramakrishna Mukkamala,et al.  Improved pulse transit time estimation by system identification analysis of proximal and distal arterial waveforms. , 2011, American journal of physiology. Heart and circulatory physiology.

[130]  Kwang Suk Park,et al.  A new approach for non-intrusive monitoring of blood pressure on a toilet seat. , 2006, Physiological measurement.

[131]  Sebastian Graf,et al.  Smart smooth muscle spring-dampers , 2007 .

[132]  L. Critchley,et al.  Impedance cardiographyThe impact of new technology , 1998, Anaesthesia.

[133]  T. Schaeffter,et al.  A Technical Assessment of Pulse Wave Velocity Algorithms Applied to Non-invasive Arterial Waveforms , 2013, Annals of Biomedical Engineering.

[134]  A. Steptoe,et al.  Pulse wave velocity as a measure of blood pressure change. , 1976, Psychophysiology.

[135]  Qiao Li,et al.  Artificial arterial blood pressure artifact models and an evaluation of a robust blood pressure and heart rate estimator , 2009, Biomedical engineering online.

[136]  K. Shelley Photoplethysmography: Beyond the Calculation of Arterial Oxygen Saturation and Heart Rate , 2007, Anesthesia and analgesia.

[137]  Lysle H. Peterson,et al.  Mechanical Properties of Arteries in Vivo , 1960 .

[138]  A. R. Lind,et al.  Comparison of physiological responses of women and men to isometric exercise. , 1975, Journal of applied physiology.

[139]  Y. Yasuda,et al.  Filtering noncorrelated noise in impedance cardiography , 1995, IEEE Transactions on Biomedical Engineering.

[140]  Yuan-Ting Zhang,et al.  Theoretical Study on the Effect of Sensor Contact Force on Pulse Transit Time , 2007, IEEE Transactions on Biomedical Engineering.

[141]  Hannu Sorvoja,et al.  Use of EMFi as a blood pressure pulse transducer , 2005, IEEE Transactions on Instrumentation and Measurement.

[142]  C. Young,et al.  Clinical evaluation of continuous noninvasive blood pressure monitoring: Accuracy and tracking capabilities , 1995, Journal of Clinical Monitoring.

[143]  David B. Newlin,et al.  Relationships ol Pulse Transmission Times to Pre-ejection Period and Blood Pressure , 1981 .

[144]  Ramakrishna Mukkamala,et al.  Perturbationless calibration of pulse transit time to blood pressure , 2012, 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[145]  A. Rovick,et al.  Influence of vascular smooth muscle on contractile mechanics and elasticity of arteries. , 1969, The American journal of physiology.

[146]  T. Palko,et al.  Ambulatory monitoring device for central hemodynamic and ECG signal recording on PCMCI flash memory cards , 1995, Computers in Cardiology 1995.

[147]  R H Cox,et al.  Regional variation of series elasticity in canine arterial smooth muscles. , 1978, The American journal of physiology.

[148]  Alberto Radaelli,et al.  Invited review: aging and the cardiovascular system. , 2003, Journal of applied physiology.

[149]  Koen D Reesink,et al.  Noninvasive Assessment of Arterial Stiffness Should Discriminate Between Systolic and Diastolic Pressure Ranges , 2010, Hypertension.

[150]  H. J. Lowe,et al.  The use of the electrical-impedance technique for the monitoring of cardiac output and limb bloodflow during anaesthesia , 1973, Medical and biological engineering.

[151]  A. Weissler,et al.  Effects of adrenergic receptor activation and blockade on the systolic preejection period, heart rate, and arterial pressure in man. , 1967, The Journal of clinical investigation.

[152]  R. Reneman,et al.  Measurement of local pulse wave velocity: effects of signal processing on precision. , 2007, Ultrasound in medicine & biology.

[153]  Yasmin,et al.  Determinants of pulse wave velocity in healthy people and in the presence of cardiovascular risk factors: ‘establishing normal and reference values’ , 2010, European heart journal.

[154]  Gilwon Yoon,et al.  Non-constrained Blood Pressure Monitoring Using ECG and PPG for Personal Healthcare , 2009, Journal of Medical Systems.

[155]  Devin B. McCombie,et al.  Motion based adaptive calibration of pulse transit time measurements to arterial blood pressure for an autonomous, wearable blood pressure monitor , 2008, 2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[156]  L A Geddes,et al.  Pulse transit time as an indicator of arterial blood pressure. , 1981, Psychophysiology.

[157]  S M M Naidu,et al.  Wavelet based denoising for suppression of respiratory and motion artifacts in impedance cardiography , 2011, 2011 Computing in Cardiology.

[158]  Ju-Won Lee,et al.  The Periodic Moving Average Filter for Removing Motion Artifacts from PPG Signals , 2007 .

[159]  P. Obrist,et al.  Pulse transit time: relationship to blood pressure and myocardial performance. , 1979, Psychophysiology.

[160]  Peter R. Smith,et al.  A new method for pulse oximetry possessing inherent insensitivity to artifact , 2001, IEEE Transactions on Biomedical Engineering.

[161]  H. Struijker‐Boudier,et al.  Expert consensus document on arterial stiffness: methodological issues and clinical applications. , 2006, European heart journal.

[162]  E. Hari Krishna,et al.  A Novel Approach for Motion Artifact Reduction in PPG Signals Based on AS-LMS Adaptive Filter , 2012, IEEE Transactions on Instrumentation and Measurement.

[163]  Carmen C. Y. Poon,et al.  An Evaluation of the Cuffless Blood Pressure Estimation Based on Pulse Transit Time Technique: a Half Year Study on Normotensive Subjects , 2009, Cardiovascular engineering.

[164]  R. Payne,et al.  Pulse transit time measured from the ECG: an unreliable marker of beat-to-beat blood pressure. , 2006, Journal of applied physiology.

[165]  K. Banitsas,et al.  A novel method to detect Heart Beat Rate using a mobile phone , 2010, 2010 Annual International Conference of the IEEE Engineering in Medicine and Biology.

[166]  K. Wesseling,et al.  Fifteen years experience with finger arterial pressure monitoring: assessment of the technology. , 1998, Cardiovascular research.

[167]  R. Light,et al.  Role of Home Blood Pressure Monitoring in Overcoming Therapeutic Inertia and Improving Hypertension Control: A Systematic Review and Meta-Analysis , 2011, Hypertension.

[168]  Alan Murray,et al.  Variability of photoplethysmography peripheral pulse measurements at the ears, thumbs and toes , 2000 .

[169]  D. Oh,et al.  Relationship between blood pressure parameters and pulse wave velocity in normotensive and hypertensive subjects: invasive study , 2007, Journal of Human Hypertension.

[170]  Tobias Schaeffter,et al.  Altered Dependence of Aortic Pulse Wave Velocity on Transmural Pressure in Hypertension Revealing Structural Change in the Aortic Wall , 2014, Hypertension.

[171]  Survi Kyal,et al.  A method to detect cardiac arrhythmias with a webcam , 2013, 2013 IEEE Signal Processing in Medicine and Biology Symposium (SPMB).

[172]  G. Parati,et al.  Wearable Seismocardiography , 2007, 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[173]  J. Nyboer,et al.  Electrical Impedance Plethysmography: A Physical and Physiologic Approach to Peripheral Vascular Study , 1950, Circulation.

[174]  Carmen C. Y. Poon,et al.  Cuff-less and Noninvasive Measurements of Arterial Blood Pressure by Pulse Transit Time , 2005, 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference.

[175]  Federico S. Cattivelli,et al.  Noninvasive Cuffless Estimation of Blood Pressure from Pulse Arrival Time and Heart Rate with Adaptive Calibration , 2009, 2009 Sixth International Workshop on Wearable and Implantable Body Sensor Networks.

[176]  Pasquale Arpaia,et al.  A piezo-film-based measurement system for global haemodynamic assessment , 2010, Physiological measurement.

[177]  M. A. Younessi Heravi,et al.  Continuous and Cuffless Blood Pressure Monitoring Based on ECG and SpO2 Signals ByUsing Microsoft Visual C Sharp , 2014, Journal of biomedical physics & engineering.

[178]  Carmen C. Y. Poon,et al.  Modeling of Pulse Transit Time under the Effects of Hydrostatic Pressure for Cuffless Blood Pressure Measurements , 2006, 2006 3rd IEEE/EMBS International Summer School on Medical Devices and Biosensors.

[179]  Steve Warren,et al.  Two-Stage Approach for Detection and Reduction of Motion Artifacts in Photoplethysmographic Data , 2010, IEEE Transactions on Biomedical Engineering.

[180]  R. Kirkpatrick,et al.  Ambulatory Blood Pressure Monitoring , 1993, The Journal of the American Board of Family Medicine.

[181]  Nicholas Bari Olivier,et al.  Improved Pulse Wave Velocity Estimation Using an Arterial Tube-Load Model , 2014, IEEE Transactions on Biomedical Engineering.

[182]  A. Murray,et al.  Repeatability of peripheral pulse measurements on ears, fingers and toes using photoelectric plethysmography. , 1988, Clinical physics and physiological measurement : an official journal of the Hospital Physicists' Association, Deutsche Gesellschaft fur Medizinische Physik and the European Federation of Organisations for Medical Physics.

[183]  G. Willemsen,et al.  Ambulatory monitoring of the impedance cardiogram. , 1996, Psychophysiology.

[184]  Weidong Wang,et al.  Motion artifact removal from photoplethysmographic signals by combining temporally constrained independent component analysis and adaptive filter , 2014, Biomedical engineering online.

[185]  Roy Kalawsky,et al.  Noncontact imaging photoplethysmography to effectively access pulse rate variability , 2012, Journal of biomedical optics.

[186]  Vijay K. Varadan,et al.  Smart healthcare textile sensor system for unhindered-pervasive health monitoring , 2012, Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[187]  T. Wibmer,et al.  Pulse transit time and blood pressure during cardiopulmonary exercise tests. , 2011, Physiological research.

[188]  P Whelton,et al.  Prevalence of hypertension in the US adult population. Results from the Third National Health and Nutrition Examination Survey, 1988-1991. , 1995, Hypertension.

[189]  P S Hamilton,et al.  Effect of adaptive motion-artifact reduction on QRS detection. , 2000, Biomedical instrumentation & technology.

[190]  Xiao Hu,et al.  A Robust Approach Toward Recognizing Valid Arterial-Blood-Pressure Pulses , 2010, IEEE Transactions on Information Technology in Biomedicine.

[191]  E. Bridges,et al.  Monitoring arterial blood pressure: what you may not know. , 2002, Critical care nurse.

[192]  T. Togawa,et al.  Continuous estimation of systolic blood pressure using the pulse arrival time and intermittent calibration , 2000, Medical and Biological Engineering and Computing.

[193]  X. Aubert,et al.  Cuffless Estimation of Systolic Blood Pressure for Short Effort Bicycle Tests: The Prominent Role of the Pre-Ejection Period , 2006, 2006 International Conference of the IEEE Engineering in Medicine and Biology Society.

[194]  Sun K. Yoo,et al.  Motion artifact reduction in photoplethysmography using independent component analysis , 2006, IEEE Transactions on Biomedical Engineering.

[195]  D. Altman,et al.  A note on the use of the intraclass correlation coefficient in the evaluation of agreement between two methods of measurement. , 1990, Computers in biology and medicine.

[196]  G. Cowper,et al.  Smooth muscle contraction and viscoelasticity of arterial wall. , 1970, Canadian journal of physiology and pharmacology.

[197]  L. Geddes,et al.  Measurements of Young's Modulus of Elasticity of the Canine Aorta with Ultrasound , 1979 .

[198]  H. Harry Asada,et al.  Cuffless Blood Pressure Monitoring Using Hydrostatic Pressure Changes , 2008, IEEE Transactions on Biomedical Engineering.

[199]  Wenli Wu,et al.  [Mobile Health: IEEE Standard for Wearable Cuffless Blood Pressure Measuring Devices]. , 2015, Zhongguo yi liao qi xie za zhi = Chinese journal of medical instrumentation.

[200]  B. Pannier,et al.  Assessment of arterial distensibility by automatic pulse wave velocity measurement. Validation and clinical application studies. , 1995, Hypertension.

[201]  Richard M. Wiard,et al.  Robust ballistocardiogram acquisition for home monitoring , 2009, Physiological measurement.

[202]  C. E. Martin,et al.  Autonomic mechanisms in hemodynamic responses to isometric exercise. , 1974, The Journal of clinical investigation.

[203]  Tomoyuki Yambe,et al.  Beat-to-beat evaluation of systolic time intervals during bicycle exercise using impedance cardiography. , 2004, The Tohoku journal of experimental medicine.

[204]  A. Patzak,et al.  Continuous blood pressure measurement by using the pulse transit time: comparison to a cuff-based method , 2011, European Journal of Applied Physiology.

[205]  D B Newlin,et al.  Relationships of pulse transmission times to pre-ejection period and blood pressure. , 1981, Psychophysiology.

[206]  P A Oberg,et al.  Photoplethysmography. Part 2. Influence of light source wavelength. , 1991, Medical & biological engineering & computing.