(12) United States Patent
`Varshneya et al.
`
`USOO6816266 B2
`US 6,816,266 B2
`*Nov. 9, 2004
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) FIBER OPTIC INTERFEROMETRIC VITAL
`SIGN MONITOR FOR USE IN MAGNETIC
`RESONANCE IMAGING, CONFINED CARE
`FACILITIES AND IN-HOSPITAL
`
`(75) Inventors: Deepak Varshneya, 3057 Caminito
`Sagunto, Del Mar, CA (US)
`92104-3934; John L. Maida, Jr.,
`Houston, TX (US); Larry A. Jeffers,
`Minerva, OH (US)
`(73) Assignee: Deepak Varshneya, Del Mar, CA (US)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 23 days.
`This patent is Subject to a terminal dis
`claimer.
`(21) Appl. No.: 10/299,414
`(22) Filed:
`Nov. 19, 2002
`(65)
`Prior Publication Data
`US 2003/0095263 A1 May 22, 2003
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 09/499,889, filed on
`Feb. 8, 2000, now Pat. No. 6,498,652.
`(51) Int. Cl." .................................................. G01B 9/02
`(52) U.S. Cl. ....................................................... 356/477
`(58) Field of Search ................................. 356/477, 478,
`356/479, 481, 483; 250/227.19, 227.27
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`5,212,379 A 5/1993 Nafarrate et al.
`(List continued on next page.)
`OTHER PUBLICATIONS
`Invivo Research, Inc., Questions & Answers from the
`JCAHO, Conscious Sedations (Questions about the Anes
`thesia Continuun by Ann Kobs, www.invivoresearch.com/
`topicS/vital Signs/caho.html.
`(List continued on next page.)
`
`Primary Examiner Samuel A. Turner
`Assistant Examiner Patrick Connolly
`(74) Attorney, Agent, or Firm-Pearne & Gordon LLP
`(57)
`ABSTRACT
`A fiber optic monitor that utilizes optical phase interferom
`etry to monitor a patient's Vital Signs. Such as respiration,
`cardiac activity, blood pressure and body's physical move
`ment. The monitor, which is non-invasive, comprises an
`optical fiber interferometer that includes an optical fiber
`proximately situated to the patient So that time varying
`acousto-mechanical Signals from the patient are coupled into
`the optical fiber. Responsive thereto, the interferometer
`generates a time-varying optical intensity resulting from the
`interference of optical Signals, which are detected at a
`photo-detector. A signal processor coupled to the optical
`detector provides one or more processed output signals
`indicative of the vital functions. The monitor system has
`broad applicability, from routine monitoring of infants at
`home to detection of apnea, arrhythmia, blood pressure and
`trauma. The System can be implemented in embodiments
`ranging from a low cost in-home monitor for infants to a
`high end product for in hospital use. The monitor can be
`integrated with other Sensors Such as an EKG, a Video or Still
`camera, an oxygen Sensor, a carbon dioxide Sensor, tem
`perature Sensor or a microphone to get additional required
`information depending on the application. When integrated
`and combined with EKG information, the monitor provides
`ballisto-mechanical information of the heart for early diag
`nosis of cardiac conditions or prediction of events or for
`correcting corrupted EKG signals due to time varying mag
`netic and electric fields. In Some embodiments of the
`monitor, the System can be made portable So that the patient
`can walk around while Still being continuously monitored
`for Vital Signs. Another Suitable design measures blood
`preSSure continuously and non-invasively by containing the
`fiber optic Sensor in a cuff that wraps around an arterial wall
`of the patient. The fiber optic monitor may be designed for
`use in a variety of Settings including an operating room, a
`recovery room, an intensive care unit, a magnetic resonance
`imaging laboratory, a computerized tomography Scan labo
`ratory and an elderly care facility.
`
`45 Claims, 14 Drawing Sheets
`
`
`
`
`
`61 O
`
`650
`
`114.
`
`DETECTOR
`
`Page 1 of 41
`
`
` EX1027
` Petitioner Sotera (RE353)
`
`

`

`US 6,816,266 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5,241,300 A 8/1993 Buschmann
`5,291,013 A 3/1994 Nafarrate et al.
`6,498,652 B1 * 12/2002 Varshneya et al. .......... 356/477
`OTHER PUBLICATIONS
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`detecting Hypoxemia and Bradycardia: Comparision
`between Nellcor N-200, N-3000 and Masimo SET(E), www.
`invivoresearch.com/topicS/vital Signs/reliability.html.
`Useful Life of Pulse Oximeter Sensors in a NICU, T.A.
`Holmes et al., www.invivoresearch.com/topicS/vital signs/
`Sensor life.html.
`Invivo Research, Inc., Advances in ECG Filtering Process
`for Patient Monitoring and Cardic Gating in MRI F.G.
`Shellock, www. invivoresearch.com/topicS/vital signs/
`moon.html.
`Several States Now Mandate Stringent Criteria for Physi
`olocigal Monitoring of Anesthetized Patents, M. Schiebler,
`etal.
`www.invivoresearch.com/topics/vital Signs/Sur
`vey.html.
`Monitoring Patients During MR Procedures: A Review, F.G.
`Shellock et al., www.invivoresearch.com/topics/vital
`Signs/review.html.
`Nornal Sinus Rhythm(NSR), www.rchcrush.edu/rmaweb
`files/abnl%20rhythm%20for%20parents%20body.htm.
`Anesthesia in the MRI Suite, hhtp://www.gasnet.org/mri/
`introduction br.php.
`Anesthesia Equipment in the MRI Suite, Charlotte Bell, MD
`and Rebecca Dubowy, MD, Department of Anesthesiology,
`Yale University School of Medicine, New Haven, CT, USA.
`www.gasnet.org/mri/about/about-mri1 br.php.
`Anesthesia Equipment in the MRI Suite, The Process of
`Magnetic Resonance Imaging, Charlotte Bell, MD et al.
`www.gasnet.org/mri/about/about-mri2 br.php.
`Anesthesia Equipment in the MRI Suite, Monitoring in the
`MRI Suite, Charlotte Bell, MD et al., www.gasnet.org/mri/
`about/about-mri3 br.php.
`MRI Patient Vital Signs Monitoring System, Product
`Description,
`www.gasnet.org/mri/equipment/invivo
`br.php.
`OptoventTM RR 9700, Respiratory rate and Apnea Monitor,
`Product Description, www.gasnet.org/mri/equipment/op
`tovent br.php.
`Datex-Ohmeda Aestive"M/5 MRIAnesthesia System, www.
`gasnet/org/mri/equipment/datex-ohmeda br.php.
`Drager, Narcomed MRI, Titus, PM 8050 MRI, www.gasne
`t.org/mri/equipment/draeger1 br.php.
`Drager, Titus, Narkomed MRI, PM 8050MI, Basic Unit,
`www.gasnet.org/mri/equipment/draeger2 br.php.
`Drager, Narkomed MRI Titus, PM8050 MRI, Ambient con
`ditions, www.gasnet.org/mri/equipment/draeger3 br.php.
`Anesthesia in the MRI Suite, biblipgraphy of suitable moni
`tors and equipment, www.gasnet.org/mri/biblipgraphy/bib
`liography 1 br.php.
`Anesthesia in the MRI Suite, bibliography of sedation/
`anesthesia techniques www.gasnet.org/mri/bibliography/
`bibliography2 br.php.
`Using Anesthesia Information Systems to Optimize After
`noon and Evening Anesthesia Staffing, F. Dexter, M.D.,
`PhD. Introduction, www.gasnet.org/mri/aims/dexter1
`br.php.
`
`Using Anesthesia Information Systems to Optimize After
`noon and Evening Anesthesia Staffing, F. Dexter, M.D.,
`PhD.
`References,
`www.gasnet.org/mri/aims/dexteriS
`br.php.
`Using Anesthesia Information Systems to Optimize After
`noon and Evening Anesthesia Staffing, F. Dexter, M.D.,
`PhD. Second-shift Staffing algorithm, www.gasnet.org/
`aims/dexter2 br.php.
`Using Anesthesia Information Systems to Optimize After
`noon and Evening Anesthesia Staffing, F. Dexter, M.D.,
`PhD. Experience in using the algorithm, www.gasnet.org/
`aims/dexter3 br.php.
`Using Anesthesia Information Systems to Optimize After
`noon and Evening Anesthesia Staffing, F. Dexter, M.D.,
`PhD. ConclusionsS, www.gasnet.org/aims/dexter4 br.php.
`Advantages and Pitfalls of Perioperative Electronic Records,
`G.L. Gibby MD, Introduction... www.gasnet.org/aims/
`gibby 1 br.php.
`Advantages and Pitfalls of Perioperative Electronic Records,
`G.L. Gibby MD, Moving Patients through the system,
`www.gasnet.org/aims/gibby 2 br.php.
`Advantages and Pitfalls of Perioperative Electronic Records,
`G.L. gibby MD, They work in our experience, www.gasnet.
`org/aims/gibby3 br.php.
`Advantages and Pitfalls of Perioperative Perioperative Elec
`tronic Records, G.L. Gibby MD, Multiple input mechanisms
`a must, www.gasnet.org/aims/gibby4 br.php.
`Advantages and Pitfalls of Perioperative Electronic Records,
`G.L. Gibby MD, Conclusion, www.gasnet.org/aims/
`gibby5 br.php.
`Advantages and Pitfalls of Perioperative Electronic Records,
`G.L. Gibby MD, References, www.gasnet.org/aims/
`gibby 6 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., Introduction www.gasnet.org/
`aims/oreilly 1 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., What is an Anesthesia Infor
`mation System?, www.gasnet.org/aims/oreilly2 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., Moving patients through the
`System, www.gasnet.org/aims/oreilly3 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., Does the patient need to be
`Seen in advance of Surgery, www.gasnet.org/aims/or
`eilly4 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., Is the patient medically ready
`to go to the OR2, www.gasnet.org/aims/oreilly5 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., Is there a practice guideline
`for this procedure? www.gasnet.org/aims/oreilly 6 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., We are the co-morbidity and
`phenotype doctors' Conclusions, www.gasnet.org/aims/or
`eilly 7 br.php.
`Anesthesia Information Systems and Perioperative Work
`Flow, Michael O'Reilly, MD., References, www.gasnet.org/
`aims/oreilly8 br.php.
`Deio specializes in clinical Information Systems (CIS),
`www.gasnet.org/aims/dateX br.php.
`DucuSys Anesthesia Information System, Product Descrip
`tion, www.gasnet.org/aims/docsys br.php.
`
`Page 2 of 41
`
`

`

`US 6,816,266 B2
`Page 3
`
`Drager Medical Saturn Information System, Product
`Description, www.gasnet.org/aim/draeger br.php.
`GE Medical Systems, Centricity TM Perioperative Anesthe
`sia, Product DeScription, www.gasnet.org/aims/gemidical
`br.php.
`GASNet Video Library, www.gasnet.org/videos/index
`br.php.
`Anesthesiologist's Manual of Surgical Procedures, Richard
`A. Jaffe et al., Raven Press, 1994 Reviewed by AB. Hilton,
`MD, www.gasnet.org/review/articleS/Surgical-procedures
`br.php.
`Clinical Transesophageal Echocardiography: A Problem
`Oriented Approach, Yasu Oka et al., 1996, www.gasnet.org/
`reviewS/article/tee br.php.
`Review: Death on Request, M. Nedorhorst, www.gasnet.
`org/reviewS/articles/death br.php.
`Book Review: Drug Infusions in Anesthesiology, 2nd Edi
`tion, R.J. Fragen, ed., Lippincott-Raven, 1996, Reviewed by
`A.M. De Wolfe, MD, www.gasnet.org/reviews/articles/
`drug-infusions br.php.
`Genetics in Anesthesiology-Syndromes and Science, Guy
`L. Weinberg, Butterworth-Heinemann, Reviewed by G.B.
`Russell, MD., mwww.gasnet.org/reviewS/article/Weinberg
`br.php.
`Book Review: Handbook of Pharmacology and Physiology
`in Anesthetic Practice, Robert K. Stoelting, Lippincott
`Raven Press, 1995, www.gasnet.org/reviews/articles/stoelt
`ing br.php.
`Book Review: The Art of Serial Communication, RWD
`Nickalls et al., www.gasnet.org/reviewS/articles/Sercom
`br.php.
`
`Book Review: With Numb toes and Arching soles: Coping
`with Peripheal Neuropathy, Reviewed by Shu-Ming Wang
`www.gasnet.org/reviews/article/numbtoes br.php.
`Book Review: Practical Anaesthesia and Analgesia for Day
`Surgery, J.M. Millar et al., Reviewed by Kathryn King MD.,
`www.gasnet.org/reviews/articles/pracanesanalg br.php.
`The Anesthesia Gas Machine, Vaporizers, Compressed
`Gases, Safety: Avoiding the Pitfalls, Michael P. Dosch,
`www.gasnet.org/machine/part1.htm.
`Invivo Research, The Agent Revolutions, Articles & Clinical
`Information
`www.inivoresearch.com/topicS/vital signs/
`agent.html.
`“Phonocardiography: Measurement of Heart Sounds',
`www.seas.Smu.edu/cd/EE5340/lect20/tsld011.htm.
`“Normal Sinus Rhythm", www.rchc.rush.edu/rmawebfiles/
`abnl%20rhythm%20for%20parents%20body.htm
`and
`www.rchc.rush.edu/rmawebfiles/
`EKG%20for%20parents%20body.htm.
`EE5340 Introduction to Biomedical Engineering-Lexture
`Slives: 368-386, http://engr.Smu.edu/~cd/EE5340/lect20/
`sld001.htm through http://engr.Smu.edu/~cd/EE5340/lect20/
`SldO201.htm.
`Catheters and Guide Wires. In Interventional MRI: Problems
`and Solutions, M.K. Konings et al. Medica Mundi, 45/1
`Mar. 2001.
`Ameerican College of Radiology White Paper on MR
`Safety, Charlotte
`Bell, MD et
`al., AJR 2002;
`178:1335-1347.
`
`* cited by examiner
`
`Page 3 of 41
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`U.S. Patent
`
`Nov. 9, 2004
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`Sheet 1 of 14
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`US 6,816,266 B2
`
`100
`
`INTERFEROMETER
`
`112
`
`10
`
`
`
`
`
`Fig.1
`
`
`
`OPTICAL
`SOURCE
`
`OPTICAL FIBER
`
`PHOTODETECTOR
`
`
`
`
`
`
`
`
`
`120
`
`122
`
`SENSOR
`PAD
`
`ACOUSTICSIGNALS
`GENERATED BY
`PHYSICAL
`FUNCTIONS
`
`
`
`PATIENT
`
`12
`4.
`
`150
`
`ADDITIONAL SENSOR(S)
`
`DISPLAY
`
`WARNING
`INDICATOR
`
`
`
`
`
`
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`
`
`
`
`pressor
`
`SEPARATED
`OUTPUT
`SIGNALS
`
`
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`
`
`DATALOG
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`AUDIBLE
`MONITOR
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`U.S. Patent
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`Nov. 9, 2004
`Nov. 9, 2004
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`US 6,816,266 B2
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`US 6,816,266 B2
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`HGHLY COHERENT
`LASER SOURCE
`
`
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`PHOTO DETECTOR
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`U.S. Patent
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`Sheet 5 of 14
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`US 6,816,266 B2
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`Coupler
`
`Fiber Bragg Grating, .
`Fray Rotator
`A.
`rot
`YA
`<=D-H -O
`L
`
`
`
`Fig. 5A
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`Page 8 of 41
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`Sheet 6 of 14
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`US 6,816,266 B2
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`
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`DETECTOR
`
`845-/-
`TO SENSOR PAD
`Figs --cr
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`Page 9 of 41
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`Sheet 7 of 14
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`US 6,816,266 B2
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`S16
`
`026
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`Nov.9, 2004
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`Sheet 9 of 14
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`US 6,816,266 B2
`US 6,816,266 B2
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`Sheet 10 of 14
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`US 6,816,266 B2
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`
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`TIME (seconds)
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`
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`Leods
`EKG Leod
`
`EKG Electrode
`
`Fig.14b
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`Page 15 of 41
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`U.S. Patent
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`Sheet 13 of 14
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`US 6,816,266 B2
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`U.S. Patent
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`Nov. 9, 2004
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`Sheet 14 of 14
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`US 6,816,266 B2
`
`Pressure
`mm Hg
`30
`
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`Page 17 of 41
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`

`US 6,816,266 B2
`
`1
`FIBER OPTIC INTERFEROMETRIC VITAL
`SIGN MONITOR FOR USE IN MAGNETIC
`RESONANCE IMAGING, CONFINED CARE
`FACILITIES AND IN-HOSPITAL
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`This is a continuation-in-part of patent application Ser.
`No. 09/499,889 entitled, “Fiber Optic Monitor Using Inter
`ferometry for Detecting Vital Signs of a Patient,” filed on
`Feb. 8, 2000 now U.S. Pat. No. 6,498,652, which is incor
`porated herein by reference in its entirety.
`
`FIELD OF THE INVENTION
`The present invention generally relates to Vital sign moni
`tors for detecting physiological parameterS Such as
`heartbeat, respiration, physical movement, blood pressure
`and other bodily activities of a patient for use in a magnetic
`resonance imaging (MRI) environment, confined care facili
`ties (e.g., geriatrics) and in-hospital during Surgery, postop
`erative recovery and intensive care units.
`
`15
`
`2
`ously. Monitoring of different Vital parameters depends on
`the patient condition Such as heart patient, pediatric or
`claustrophobic and the type of anesthesia administered. In
`the past, the attending anesthesiologist made the decision.
`More recently, the American Society for Anesthesia has
`published guidelines describing both the physiological
`monitoring equipment and parameters that must be mea
`sured for different patient types (“Both sedated and critically
`III require Monitoring during MRI, Mark Schiebler, MD, et
`al. www.invivoresearch.com/topics/vital signs/Survey.html)
`and White Paper on “MRI Safety”, Charlotte Bell, MD, et
`al., American College of Radiology, AJR 2002;
`178:1335–1347). According to these guidelines, the key
`parameters that must be continuously monitored include:
`EKG, Pulse Oximetry, Blood pressure, and Respiration by
`end tidal CO/Capnograph or other methods.
`Generally the three broad categories of problems are
`experienced when monitoring the Vital Signs of Sedated
`patients in the MRI: 1) MRI environment induced interfer
`ence in the vital sign monitoring equipment; 2) inadequate
`monitoring of respiration due to long Separation between the
`patient and equipment producing latencies, and blockages in
`capnograph equipment lines; and 3) use of conventional
`ferrous-based EKG electrodes and lines cause burns to
`patients. Therefore the real time control is compromised.
`Each of the above problems has been addressed in light of
`the monitoring equipment. Because the key-monitoring
`equipment used in detecting the Vital Signs in the MRI
`environment is the EKG, a brief interpretation of the EKG
`waveforms and problems associated with them during the
`Scanning is provided below.
`The electrocardiogram (EKG) measures changes in skin
`electrical Voltage/potential caused by electrical currents gen
`erated by the myocardium. This electrical activity is typi
`cally represented by PQRST waveforms. The Pwave reflects
`atrial depolarisation, while the QRS complex represents
`Ventricular depolarisation, and the T wave Ventricular repo
`larisation. Repolarisation is a process that occurs in many
`cells where the electrical potential acroSS the cell membrane
`returns from the value during the action potential to that of
`the resting State (the resting membrane potential). Although
`the EKG shows heart rate and rhythm and can indicate
`myocardial damage, it does not directly give information on
`the adequacy of contraction. Normal electrical complexes
`can exist in the absence of cardiac output, a State known as
`pulseless electrical activity or electromechanical dissocia
`tion (EMD). The pulseless behavior is a special case of the
`myocardium but generally there is a direct correlation
`between the electrical activity as measured by the EKG with
`the mechanical activity as measured by phonocardiography.
`The foregoing is known to those skilled in the art and
`described in, “Phonocardiography: Measurement of Heart
`Sounds', www.seas. Smu.edu/~cd/EE5340/lect 20/
`tsld011.htm, which is incorporated herein by reference in its
`entirety.
`The EKG is generated using the 3, 5 or 12 lead configu
`ration depending on the circumstances. For example in the
`MRI, usually 3 or 5 lead EKG is used because the patient is
`imaged while Sedated but does not undergo Surgery. At the
`end of each lead is an electrode that measures the Small
`potential difference produced as a result of heart's electrical
`activity. By measuring for example the Rate, Rhythm,
`Impulse Axis, Hypertrophy and Infarction, information
`about the heart condition can be determined. These charac
`teristic parameters are determined from the data manifested
`in V1 through V6 leads placed on Specific locations on the
`chest and 1, 2, 3, AVR, AVL and AVF leads placed on the
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`DESCRIPTION OF RELATED ART
`1. Background of Vital Sign Monitoring in Magnetic Reso
`nance Imaging Labs
`Use of Magnetic Resonance Imaging (MRI) is rapidly
`growing in the U.S. and other parts of the world for
`investigations and diagnosis of many diseases. Statistical
`data published by In-vivo Research shows that over 18
`million Scans are performed per year in the U.S. alone. To
`better understand the problems of monitoring patients under
`going MRI scanning, a Summary of the key Steps required in
`generating a patient's image is provided:
`1. A Strong magnetic field, on the order of 1.5 to 2 Teslas
`(1 Tesla=10,000 Gauss, earth's magnetic field is 1 Gauss), is
`required to align all randomly oriented nuclei cells of the
`patient;
`2. Radio frequency (RF) pulses, directed at the patient, are
`used in the presence of the external magnetic field, to cause
`the cell nuclei to absorb more energy producing magnetic
`resonance. This is generally referred to as Super charging of
`the nuclei, which further changes their alignment from the
`original State;
`3. The RF Supercharged cell nuclei recover their original
`State of alignment within the magnetic field by re-emitting
`the absorbed RF energy. The RF signal re-emitted by each
`tissue is proportional to the difference between the energized
`magnetic resonance States and the original alignment States.
`TiSSue imaging contrast develops as a result of the different
`rates of realignment;
`4. Time varied magnetic field (TVMF) gradients are
`applied briefly to Spatially encode the RF signals emitted
`from the patient tissues,
`5. The RF coils in the MRI pick up these spatially encoded
`RF signals emitted from the tissues and are transformed by
`a computer into 2 or 3 dimensional images.
`The strong magnetic field, RF pulses and/or TVMF gra
`dients are referred to in this disclosure as “the MRI envi
`ronment.
`Of the 18 million MRI scans done per year, approximately
`10% of the patients are Sedated during Scanning for a variety
`of reasons. These patients are Sedated using general, con
`Scious intravenous (IV, Spinal and epidural), orally admin
`istered (chewing tablets) or local anesthesia. If anesthesia is
`65
`administered during MRI scanning, the law generally man
`dates that the patient's Vital Signs be monitored continu
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`limbs, etc. Normal and abnormal rate and rhythm EKG
`waveforms that could be used to monitor Vital signs as well
`as to determine other heart conditions are known to those
`skilled in the art and described in the article “Normal Sinus
`Rhythm”, w w w.rch c. rush.edu/rm a web files/
`abnl%20rhythm%20for%20parent %20body.htm and
`www.rch c. rush. edu/rm a web files/
`EKG%20for%20parents%20body.htm, which are incorpo
`rated herein by reference in their entireties.
`Using the empirically correlated data not only provides
`clinical information about the five aspects of the heart's
`electrical activity but also provides variations that reflect
`other heart conditions associated within each of the five
`categories. It is well documented in the literature that the P
`wave Signifies the generation of electrical impulses from the
`SA node, which travels down the AV node into the myocar
`dial cells. The QRS complex represents the electrical
`impulse when it travels from the AV node into the Purkinje
`fibers into the myocardial cells and produces Ventricular
`contractions. This signal can therefore provide information
`about the mechanical contraction of the heart's Ventricles,
`which is followed by its relaxation (process of
`repolarization). This characteristic signal when used by
`itself or in conjunction with other waveforms reveals many
`heart conditions Such as arrhythmias, abnormal rates and
`infarctions; provided the EKG waveforms are not corrupted.
`A number of manufacturers Such as HP, Colin Medical
`etc. make Vital Sign monitoring Systems that are frequently
`used in operating rooms and outpatient Surgical environ
`ments. These Systems provide continuous monitoring capa
`bility of the EKG, pulse Oximetry, blood pressure, respira
`tion rates via end-tidal CO, etc. However, it has been
`observed that these monitors do not work well in the MRI
`environment. It is found that the EKG waveform is cor
`rupted due to Strong Static magnetic fields, RF pulses, and
`the TVMF. For patients oriented in the Supine position in the
`MRI scanner (Anesthesia Equipment in the MRI Suite”,
`Charlotte Bell, MD and Rebecca Dubowy, MD, Department
`of Anesthesiology, Yale University School of Medicine,
`New Haven, Conn., USA. www.gasnet.org/mri/about/about
`mri3 brphb), the following effects are observed in the
`output EKG waveforms and the associated hardware:
`1. The Static magnetic field induces maximum Voltage
`charges in the conducting blood column within the trans
`verse aorta since it is 90 degrees to the field (Peden, et.al.
`1992 cited in “Anesthesia Equipment in the MRI Suite,
`Charlotte Bell, MD and Rebecca Dubowy, MD, Departnent
`of Anesthesiology, Yale University School of Medicine,
`New Haven, Conn. USA"). These charges are superimposed
`on the EKG waveform and are observed to be greatest in the
`ST segments and T waves in leads I, II, V1,V2 elevating the
`waveforms. The elevation of the waveforms increases with
`increasing magnetic field strength and can mimic EKG
`changes of myocardial injury.
`2. Spike artifacts that mimic R waves of the EKG are
`produced when the magnetic field gradients are applied for
`imaging the tissue along with the RF pulses. These artifacts
`can Simulate arrhythmias and produce an error in heart rate.
`3. The pulsed RF field produces heating of the leads and
`electrodes (Catheters and Guide wires in interventional
`MRI: Problems and Solutions, M. K. Konings, et. al, Medica
`Mundi, 45/1 March 2001).
`The first two effects corrupt the true EKG waveform and
`make it difficult to interpret the patient condition while the
`third effect causes skin bums. As a result, several MRI
`compatible EKG monitoring Systems have been developed
`utilizing EKG electrodes and leads made of carbon graphite
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`4
`VS. the typical Ag/AgCl. The carbon graphite material is
`used to lower resistance at these RF frequencies and elimi
`nate ferromagnetism So that the interference induced heating
`is minimized. Additionally, filters are used in the Signal
`processing to minimize artifacts. Although using graphite
`electrodes, Special filters, ensuring cable Straightness, and
`placing towels on the patient's chest minimizes the skin
`bums, the false R spikes, elevated ST segment and T
`waveforms are still manifested in the EKG when the mag
`netic field gradients and RF field are applied.
`Other techniques such as Pulse Oximetry Plethysmogra
`phy have been used as a heart tachometer (mechanical
`motion Sensor), but they are not useful for ischemia or
`arrhythmia detection. They provide delayed response and
`are unable to discern all four heart Sounds. Telemetry units
`have been used with low magnetic fields (0.6T), but gener
`ally interfere with the RF needed for imaging (Barnett, et. al.
`1988, McArdle, et. al. 1986 cited in “Anesthesia Equipment
`in the MRI Suite”, Charlotte Bell, MD and Rebecca
`Dubowy, MD). Therefore, the presence of false R spikes,
`elevated ST Segment and T waves give incorrect rates and
`rhythms, which leads to misinterpretations and misdiagnosis
`and makes it impossible to reliably detect ischemia or
`arrhythmias (ventricular or atrial flutter/fibrillation); the
`Worst two life threatening conditions. Because presently
`there are no alternatives, for patients that are highly Suscep
`tible to ischemia and arrhythmias, a 12-lead EKG pre and
`post MRI scanning is recommended. If an unstable condi
`tion arises, the patient is removed from the magnetic field for
`proper EKG analysis and treatment, which is the common
`procedure as Suggested by the MRI panel.
`For respiration monitoring, the airway adapter based
`capnograph requires long tubes between the patient and the
`monitoring equipment. These not only get plugged due to
`patient mucous but also introduce unacceptable data latency
`and therefore cannot be used in reliably measuring respira
`tion. To eliminate data latency, long tubes were replaced
`with fiber optic Sensors that were mounted in the airway
`adapter and could replace the electrical Sensors at the end of
`the tubes to directly measure the airflow. Optovent RR 9700
`builds a fiber optic based device, which detects the respira
`tion rate by measuring the flow of air via an airway adapter
`VS. chest wall movement using inductance plethysmography.
`Although this technology is immune to the MRI
`environment, it is insufficient to eliminate the adapter block
`age. Additionally, adapter based Sensors are invasive and are
`uncomfortable, producing logistical and control problems
`during the procedure.
`Clearly EKG and airway adapter based technologies that
`are electrical in nature are insufficient and unreliable for
`detecting the Vital signs (rate, rhythm and respiration) during
`MRI scans because of the presence of artifact Spikes,
`elevated ST Segments that corrupt the interpretation and
`delayed response with insufficient resolution. This greatly
`impedes the reliability of monitoring the Vital Signs espe
`cially in patients that are Sedated or have heart conditions.
`Therefore, different technologies are required in the MRI
`environment that are neither electrical in nature nor are
`airway adapter based for the measurement of heart rate,
`rhythm, and respiration. Reliable data must be continuously
`processed from the uncorrupted R-R' intervals and the QRS
`characteristics for the myocardial information while a dif
`ferent method to measure respiration is required.
`2. Background of Monitoring in Confined Care Facilities
`A class of patients (usually but not exclusively elderly)
`are mostly confined to their beds or rooms for periods of
`time during their treatment or monitoring Such as at elderly
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`care facilities, nursing homes, hospice and convalescent
`homes, Sanatoriums or insane asylums, centers for recovery
`from drug and alcohol abuse and related facilities (referred
`to herein as “confined care facilities’). These patients
`require Substantial or constant oversight to monitor their
`well-being and whereabouts within the facilities usually
`over the long term. Ideally, a nurse or other caregiver would
`attend the patient’s bedside at all times. However, it is
`generally impractical and uneconomical to provide this level
`of care at these facilities. Typically, a few Staff perSonnel
`Serve many patients periodically checking on the Status of
`individual patients. Because the caregiverS/staff are not
`constantly aware of the condition of each patient, Serious
`problems can develop. A patient may leave their bed, either
`intentionally or accidentally. Even if intentional, the patient
`may take a fall or become disoriented without being able to
`timely press the emergency button to Seek help. Dementia
`patients wander off from their rooms or the facility alto
`gether making it difficult for the staff to determine their
`whereabouts. With only periodic visual checks by the staff
`and no capability to determine their whereabouts, the patient
`may be exposed to extended periods of physical and/or
`mental distress before being located and rendered help to
`prevent untimely deaths.
`3. Background of Vital Sign Monitoring in Hospitals
`Continuous and real-time measurement of human physi
`ological parameters, Such as respiration, heart rate, blood
`preSSure and oxygenation, can be essential to the preserva
`tion of life in numerous clinical Settings, including the
`operating rooms (OR) during procedural Sedation, in inten
`Sive care units (ICU) and recovery rooms. Indeed, in most
`industria