US005919149A
`5,919,149
`(114) Patent Number:
`United States Patent 55
`
`Allum
`[45] Date of Patent:
`Jul. 6, 1999
`
`[54] METHOD AND APPARATUS FOR ANGULAR
`POSITION AND VELOCITY BASED
`DETERMINATION OF BODY SWAY FOR
`THE DIAGNOSIS AND REHABILITATION OF
`BALANCE AND GAIT DISORDERS
`
`[76]
`
`Inventor:
`
`John H. Allum, Hebel Str. 109, Basel,
`Switzerland, CH-4056
`
`[21] Appl. No.: 08/818,319
`— ,
`Filed:
`Mar. 14, 1997
`
`[22]
`
`Related U.S. Application Data
`
`[60]
`Provisional application No. 60/029,010, Oct. 24, 1996.
`[51]
`... A6LB 5/103
`Int. CL? ...
`
`[52] U.S. Cle cesscssssuseseuneneneummamenenenense 600/595
`[58] Field of Search woucccc cece 600/587, 595;
`73/862.042, 865.4
`
`[56]
`
`References Cited
`
`3,000,226
`090,
`4,092,633
`4,738,269
`4,817,633
`4,830,024
`4,848,358
`4,938,476
`5,052,406
`5,209,240
`5,281,957
`o337757
`
`5,361,778
`5,368,042
`5,469,861
`5,551,445
`5,627,327
`5,749,372
`
`U.S. PATENT DOCUMENTS
`600/595
`5/1963. Corti
`et
`al
`Ort et
`ab. eee ceeceseeeeeeeeee
`5/1978 Fletcheret al. sesssscsssseeen 340/213 R
`4/1988 Nashner cessscssssssssssssssssseeseee 128/782
`4/1989 McStravick et al.
`sesso 128/782
`
`5/1989 Nashneret al. cece 128/787
`
`7/1989 Nitzan etal. ......
`veeeee 128/740
`
`7/1990 Brunelle et al.
`...
`seveee 600/595
`......ccececeeereesceeeeeee 128/782
`10/1991 Nashiner
`5/1993)
`Jain et al. ieee eeeceeeeeeeneeee 128/779
`
`1/1994 Schoolman wessessecresreseeeseernsennes 345/8
`8)food nashneret a
`“ eree
`
`
`128/779
`11/1994 Seitz oe.
`
`.. 600/595
`11/1994 O’Neil et al.
`..
`
`i 128/781
`11/1995 Piscopoetal.
`
`9/1996 Nashner .....ecesssessesseeeseeees 128/782
`
`5/1997 Zanakis......
`. 73/862.042
`5/1998 Allen et al. wocccesceeeeees 600/595
`
`FOREIGN PATENT DOCUMENTS
`3416873 Al
`11/1985 Germany .
`WO88/04909
`7/1988 WIPO.
`
` 1
`
`OTHER PUBLICATIONS
`
`G.H. Begbie, “Some Problemsof Postural Sway”, in “Myo-
`tatic, Kinesthetic and Vestibular Mechanisms”, pp. 80-104
`(A.VS. deReuck & Julie Knight, eds., 1967).
`L.M. Nashner, “A Model Describing Vestibular Detection of
`Body Sway Motion”, Acta Otolaryng 72, pp. 429-436,
`1971.
`
`E.V. Gurfinkel, “Physical Foundations of the Stabilogra-
`phy”, Agressologie, 14, C, pp. 9-14, 1973.
`
`(List continued on next page.)
`
`Primary Examiner—Max Hindenburg
`Attorney, Agent, or Firm—Foley & Lardner
`57]
`ABSTRACT
`A method and apparatus for the diagnosis and rehabilitation
`of abnormal postural sway of a subject during standing or
`the performance of movementtasks is provided. Body sway
`sensors, such as angular velocity transducers, are attached to
`the body, such as the upper torso, of the subject. Output
`signals from the body sway sensors are transformed into
`detailed body sway angular displacement and velocity infor-
`.
`Neck,n by a een eyinforn The bodysway pogwlar
`placement anc’ velocity information may be
`displayed
`to
`an operator for diagnosis of the subject’s balance or gait
`disorders. The angular displacement and velocity informa-
`tion may also be provided as feedback to the subject,
`to
`augmentthe signals normally used by the subject’s brain to
`help stabilize body sway and improve balance. Rehabilitory
`feedback may be in visual, auditory, and/or tactile form,
`and/or in the form of electrical stimulation of the vestibular
`nerve. For visual feedback, a lightweight imaging system
`mounted on a pair of eyewear may be used to project a body
`sway angle and angular velocity feedback display into an
`eye of the subject. An angular position and velocity based
`body sway diagnosis system in accordance with the present
`invention may be used to monitor simultaneously the body
`sway of multiple subjects, and to provide rehabilitory feed-
`back to such subjects, without interfering with orrestricting
`the normal movementactivities of the subjects.
`
`67 Claims, 5 Drawing Sheets
`
`APPLE 1008
`
`APPLE 1008
`
`1
`
`

`

`5,919,149
`Page 2
`
`OTHER PUBLICATIONS
`
`J. Dichgans,et al., “Postural Sway in Normals and Atactic
`Patients: Analysis of the Stabilizing and Destabilizing
`Effects of Vision”, Agressologie 17, C, pp. 15-24, 1976.
`L.M. Nashner, “Adapting Reflexes Controlling the Human
`Posture”, Exp. Brain Res., vol. 26, pp. 59-72, 1976.
`S.H. Koozekanani, “On the Role of Dynamic Models in
`Quantitative Posturography”, IEEE Trans. Biomed. Eng.,
`vol. BME-27, No. 10, pp. 605-609, Oct. 1980.
`F. OwenBlack,etal., “Effects of Visual and Support Surface
`Orientation References Upon Postural Control in Vestibular
`Deficient Subjects”, Acta Otolaryngol 95, pp. 199-210,
`1983.
`
`Mary E.Tinetti, et al., “Fall Risk Index for Elderly Patients
`Based on Number of Chronic Disabilities’, Am. J. Med.,
`vol. 80, pp. 429-434, Mar. 1996.
`F. Owen Black,et al., “Effects of Unilateral Loss of Vesti-
`bular Function on the Vestibulo—Ocular Reflex and Postural
`
`Control”, Ann. Otol. Rhinol. Laryngol. 98, pp. 884-889,
`1989.
`
`Emily A. Keshner & John HJ. Allum, “Muscle Activation
`Patterns Coordinating Postural Stability from Head to Foot”,
`in “Multiple Muscle Systems: Biomechanics and Movement
`Organization”, pp. 481-497, (J.M. Winters & S.L—Y. Woo,
`eds., 1990).
`Kamran Barin, “Dynamic Posturography: Analysis of Error
`in Force Plate Measurement of Postural Sway”, IEEE Eng.
`in Med. Biol., vol. 11, No. 4, pp. 52-56, Dec., 1992,
`
`D. Perennou, et al., “Optoelectronic assessment of upper
`body sway in erect posture: validation for 3-D stabilom-
`etry”,
`in “Vestibular and neural front”, pp. 57-60,
`(K.
`Taguchi, et al., eds., 1994).
`Y. Ehara, et al., “Comparison of the performance of 3D
`camera systems”, Gait & Posture, vol. 3, pp. 166-169, Sep.
`1995.
`
`ThomasE. Prieto, et al., “Measures of Postural Steadiness:
`Differences Between Healthy Young and Elderly Adults”,
`IEEE Trans. Biomed. Eng., vol. 43, No. 9, pp. 956-966, Sep.
`1996.
`
`2
`
`

`

`U.S. Patent
`
`Jul. 6, 1999
`
`Sheet 1 of 5
`
`5,919,149
`
`Memory
`
`10
`
`\
`
`Angular
`Rate
`Transducer
`
`{\
`
`24
`
`Subject's
`Visual
`Display
`
`Feedback
`
`Subject's
`Auditory
`
`Display
`
`
`
` Operator's
`
`
` Printer/
`
`Plotter Operator's
`
`
`Input
`
` 22:
`
`
`
`Subject's
`Tactical
`Feedback
`
`Subject's
`Electro-
`Vestibular
`Feedback
`
`28
`
`30
`
`Fig.l
`
`3
`
`

`

`5,919,149
`
`Jul. 6, 1999
`
`Sheet 2 of 5
`
`U.S. Patent
`
`
`
`4
`
`

`

`U.S. Patent
`
`Jul. 6, 1999
`
`Sheet 3 of 5
`
`5,919,149
`
`40
`
`Path Deg
`300
`250
`200t
`150
`400
`50
`
`64
`
`% cone of
`Stability
`80
`60-
`40
`20
`
`74
`
`0
`
`0
`
`RMS Velocity
`
`20
`15
`10+
`5
`
`0
`
`66
`
`68
`
`'
`
`Roll
`Stability
`Left
`Right
`
`Pitch
`Stability
`Forw Backw
`
`deg
`
`e5—43] 75-47] 67-8| 43
`
`VLE.
`TLD|TL.
`LLL
`
`=
`
`=
`
`ldeg/S
`
`40
`
`20
`
`0
`
`20
`
`40
`Deg/Sec
`Roll
`
`o BR
`
`tS ©
`
`~~
`
`oOoO
`
`Fig.3
`
`5
`
`

`

`U.S. Patent
`
`Jul. 6, 1999
`
`Sheet 4 of 5
`
`5,919,149
`
`24
`
`80
`
`88 (aAatvsa.*afs*~*it.
`
`Fig.4
`
`>
`
`9
`
`90
`
`102 /
`
`od
`
`106
`
`<1]
`
`400
`
`104
`
`108
`
`Nw
`
`6
`
`

`

`U.S. Patent
`
`Jul. 6, 1999
`
`Sheet 5 of 5
`
`5,919,149
`
`
`
`
`
`
`Initialize Sensors, Displays, and Interfaces
`
`
`Begin Sheil Program
`
`Select Task Type
`
`Select Cone of Stability
`
`
`Set Task Parameters
`
`122
`
`124
`
`120
`
`
`
`
`128
`
`130
`
`Begin Real-Time Data Collection and Reduction|——132
`
`
`
`
`
`
`
`
`
`Modify Feedback
`Gain Sensitivity
`
`156
`
`End Real-Time Data Collection
`Begin Final Data
`Reduction and Display
`
`142
`
`444
`
`Issue Fall Warnings
`
`Log Fall Warnings
`
`
`
`150
`
`152
`
`154
`
`Display Results and
`Comparison Data
`
`Store Results in
`Storage Medium
`
`Print Results
`
`Fig.6
`
`7
`
`

`

`5,919,149
`
`1
`METHOD AND APPARATUS FOR ANGULAR
`POSITION AND VELOCITY BASED
`DETERMINATION OF BODY SWAY FOR
`THE DIAGNOSIS AND REHABILITATION OF
`BALANCE AND GAIT DISORDERS
`
`This application claims the benefit of U.S. Provisional
`Application No. 60/029,010, filed Oct. 24, 1996.
`
`FIELD OF THE INVENTION
`
`This invention pertains generally to methods and devices
`for providing non-invasive testing of the postural sway of a
`humansubject during standing or movementtasks, and more
`particularly to such methods and devices that employ direct
`measurementof body position using displacement or motion
`transducers or other sensing devices attached to the body.
`This invention also pertains generally to prosthetic methods
`and devices for aiding in the rehabilitation of balance and
`gait deficits and, more particularly,
`to such methods and
`devices that provide feedback of postural information to the
`subject.
`
`BACKGROUND OF THE INVENTION
`
`Individuals who suffer from a balance control deficit are
`
`abnormally proneto falling and have poorgait control when
`walking or engaging in other movement tasks. A balance
`control deficit may be the result of a wide variety of sensory
`and/or motor disorders that impair the posture and equilib-
`rium control of the subject. In order to make a correct
`assessmentof a subject’s balance deficit, and thereby to take
`remedial measures, an examining physician, or physical
`therapist, must determine the subject’s balance control abil-
`ity for a numberof motortasks, such as standing, getting up
`out of a chair, walking downsteps, etc. By observing the
`subject performing such motortasks, the physician may be
`able to determine if the subject’s balance control is within
`normal limits and, if not, how best to bring balance control
`near or within normal limits again. However, to provide a
`more accurate and objective assessment of the individual’s
`sensory and motor components of posture and equilibrium,
`a test system which provides an objective quantifiable
`assessment of balance control is required.
`Quantitative information on the human sense of balance
`can be obtained using a variety of methods and devices.
`Quantitative information on the efficacy of the human sense
`of balance can be obtained by the electrophysiological
`measurement of eye movementsor of the postural responses
`of the limbs. A balance control deficit
`is indicated if a
`
`response is outside of the limits expected for individuals
`having a normal balance function. Quantitative postural
`information may also be obtained by measuring contractile
`activity of the muscles generating the internal body forces
`for maintaining the equilibrium position using electromyo-
`graphic (EMG)recordings.
`Balance deficits are, however, normally quantified by
`recording body sway,i.e., the displacementof the body from
`the equilibrium position. Quantification of the postural sway
`of a subject is known as “stabilometry”or “posturography”.
`One such method for quantifying balance deficits involves
`the measurement of body sway in terms of displacement of
`the center of foot pressure (CFP), sometimes termed “center
`of force”, generated by the inherent instability of a test
`subject standing on a fixed support surface. CFP is computed
`from the signals provided by force transducers which are
`typically embedded in the four corners of the support
`surface. The force transducer outputs are employed to obtain
`
`2
`a projection, on the support surface platform,of the resultant
`forces acting at the subject’s center of gravity. An anterior,
`front-to-back, projection is obtained by assuming that the
`difference between the force detected by the for andaft force
`transducer-pairs equals torque about the ankle joint. The
`anterior projection is obtained by dividing the ankle torque
`by the total vertical force. This calculation also assumesthat
`the upright body can be represented by a simple upright
`pendulum. Thus, only the effect of movement at the ankle
`joints is considered, the effect of movements at the knee and
`hip joints is ignored. A similar calculation employs the
`signals provided by the lateral pairs of force transducers on
`each side of the support platform to obtain a lateral force
`projection. The vectorial sum of the anterior and lateral force
`projections equals the CFP. As body sway frequencies
`exceed 0.2 Hz, however, this method for estimating the
`movement of the body’s center of gravity based on CFP
`becomesincreasingly inaccurate, because oscillations of the
`upper body enter the CFP measurements as inertial reaction
`forces. Furthermore, if the multi-link nature of the body is
`ignored, serious errors in understanding a subject’s balance
`disorders can occur.
`
`Investigators have used different types of force platforms
`to analyze postural sway. Some such force platforms are
`specifically targeted towards tests for analyzing balance
`disorders caused by vestibular deficits. Quantitative exami-
`nation of CFP data suggests that subjects having a unilateral
`vestibular balance deficit, e.g., a balance deficit caused
`solely by impairmentof the vestibular end organsin the ear,
`perform within normal ranges when tests are employed
`using a fixed force sensitive support surface to perform the
`balance tests. For this reason, techniques have been intro-
`duced which make the control of spontaneous sway by a
`subject positioned on the CFP measuring support surface
`more difficult. These techniques make quantification of a
`vestibular balance deficit easier by interrupting the non-
`vestibular sensory inputs that the subject may otherwise use
`to maintain his balance. One such technique involves mov-
`ing the support surface so that
`it
`is tilted (forward or
`backward) in relation to changes in the subject’s CFP. This
`type of controlled platform instability may be obtained using
`a purely mechanical device, or with a more flexible elec-
`tronic and computer controlled motor unit. The movementof
`the support surface platform disrupts the somatosensory
`inputs which would otherwise be available to the subject. A
`second technique involves the use of a movable visual
`surround, which surrounds the subject, and which is moved
`to follow the subject’s body sway, as estimated by CFP
`measurement of the subject. This technique disrupts the
`visual stabilization inputs used by the subject to maintain
`balance control. By disrupting the somatosensory and visual
`inputs, a test procedure for analyzing a subject’s balance
`control is able to focus more particularly on the vestibular
`balance control mechanism. Examples of such test systems
`and procedures are described in more detail in U.S. Pat. Nos.
`4,738,269, 5,052,406, and 5,303,715 issued to Nashner, et
`al. Analysis of tests employing these improvements to CFP
`sway quantification have indicated that destabilization of the
`support surface beneath the subject provides a major diag-
`nostic improvement. However, destabilizing a visual sur-
`round by moving it in relation to the CFP provides little
`additional diagnostic information asfar as vestibular balance
`deficit is concerned.
`
`A major drawback of CFP based systems for quantifying
`body sway is that the freedom of movementof the subject
`is limited by the fact that the subject must remain in contact
`with the force sensing support surface. Thus, the physician’s
`
`wn
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`
`8
`
`

`

`5,919,149
`
`3
`ability to determine a subject’s balance control while per-
`forming a variety of motor tasks is limited by the CFP
`method. A moreflexible system that may be used to measure
`body sway employslight-weight light-emitting sources that
`are mounted on a subject’s body. However, such three-
`dimensional camera based systems are typically prohibi-
`tively expensive for most physical therapy practices special-
`izing in rehabilitation of gait and balance deficits. Moreover,
`these systems also have a numberof technical drawbacks,
`including excessive computer power requirements, limited
`on-line capabilities, sensitivity to interfering light sources,
`and limited range of operation. Thus, although such systems
`are capable of quantifying gait and other dynamic postural
`abnormalities, which cannot be achieved using CFP mea-
`suring support surfaces, this advantage is outweighed by the
`price and ease-of-operation advantages of more conven-
`tional CFP systems. Thus, CFP systemsare still the system
`of choice for quantifying the body sway of subjects with
`balance deficits.
`
`After a balance deficit has been diagnosed and quantified,
`a physician may prescribe remedial measures to bring the
`subject’s balance control near or within normal limits. The
`physician may prescribe medication that reduces the action
`of peripheral senses on the brain. Alternatively, the physi-
`cian may prescribe a course of physical therapy, which will
`typically last at
`least several weeks, with the object of
`training the subject’s brain to deal with a reduced sense of
`balance when trying to maintain the body upright and
`prevent a fall. However, neither of these techniques will
`have an immediate rehabilitory effect on the subject’s bal-
`ance deficit. Moreover, medication can haveside effects, and
`can also reduce the capability of the brain to process balance
`information from the peripheral senses. A course of physical
`therapy requires a long training period which may extend
`over more than two months. These difficulties and limita-
`tions associated with conventional remedial measures for
`
`dealing with balance deficits are most problematic when the
`subject is older and likely to have a falling tendency.
`In the field of hearing, which is physiologically related to
`that of balance, two types of prostheses are used to augment
`a subject’s hearing ability. The first type of device involves
`augmenting the sound wavesin the external ear canal so that
`they have greater excursions when they reach the inner ear
`where they are transduced into electrical signals that reach
`the brain. The second type of device for improving hearing
`ability involves direct electrical stimulation of the auditory
`nerve in the inner ear. For the sense of balance, however, in
`which sensory signals from different neurophysiological
`systems, including a major input from the vestibular system
`of the inner ear, are combined bythe brain to yield a unitary
`sense of balance, no prosthetic device exists.
`
`SUMMARYOF THE INVENTION
`
`The present invention provides a method and apparatus
`for performing non-invasive, sensitive, and reliable tests for
`the presence of abnormalities in the postural sway of a
`human subject during standing or movement
`tasks. A
`method or device in accordance with the present invention
`may be used as both a diagnostic and a rehabilitory tool for
`subjects who are prone to abnormal falling or who wish to
`improve their movementcontrol. The present invention may
`specifically be used to provide prosthetic feedback to aid in
`the rehabilitation of balance and gait deficits.
`The method and apparatus of the present invention is
`based on the finding that
`the unitary sense of balance
`computed by the human brain involves monitoring the upper
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`55
`
`60
`
`65
`
`4
`body and maintaining the angular position and angular
`velocity of the body within a cone of angular stability. Once
`this cone of stability is exceeded, with an excessive angular
`velocity, normal individuals will respond by correcting the
`trunk position within 200 milliseconds.
`The present
`invention employs light-weight wearable
`body sway sensors, such as velocity transducers, that are
`preferably attached to the upper body, e.g., the chest, of a
`subject. The sensor output signals are transformed into
`detailed angular displacement and velocity information. The
`subject need not remain in contact with a support-surface in
`order for body sway measurements to be made, therefore,
`subject movementis notrestricted. Moreover, the body sway
`sensors employed in the present invention are not limited in
`accuracy by the assumptionsused for calculating body sway
`based on CFPfrom the signals provided by force transducers
`embedded in a force plate support surface.
`Signals from the body sway sensors on the subject are
`provided to a microprocessor based system processor. The
`system processor is programmed to transform the angular
`position and velocity information provided by the sensors
`into useful information formats that are displayed to an
`operator on an operator’s display unit. Quantified body sway
`information that may be provided to the operator as part of
`the operator’s display includes: time histories of the sub-
`ject’s angular sway deviations and angular velocity in the
`roll and pitch directions, histograms of the sway deviations
`and sway velocities over an examination trial period for the
`roll and pitch directions, a measurementof thetotal vectorial
`angular path transversed by the subject’s upper body during
`the examination trial period, and measures of maximum
`instability in the roll and pitch directions. The operator’s
`display may also provide for comparisons between exami-
`nation trial results from different trials or between exami-
`
`nation trial results and body sway information obtained from
`a normal sample population. Moreover, the operator’s dis-
`play may provide an objective measure of the subject’s
`stability by comparison of the subject’s zero-velocity cone
`of stability with the maximum trunk sway angle deviations
`occurring during the examination trial period. Since the
`body sway sensors employed by the present invention do not
`interfere with subject movement, this detailed information
`may be obtained for examination trials involving the per-
`formance of a wide variety of movement
`tasks by the
`subject.
`The system processorof the present invention mayalso be
`programmedto provide rehabilitory postural feedbackto the
`subject based upon the body sway angle and sway velocity
`information obtained from the body sway sensors. This
`feedback may be in the form of visual, auditory, or tactile
`stimulation, or may be provided in the form of an electrical
`signal that is used to directly stimulate the vestibular nerve.
`Asingle type of feedback maybe used,or different types of
`feedback may be provided to a subject in combination. The
`rehabilitory feedback immediately augments the balance
`signals normally used by the subject’s brain to help stabilize
`body sway and improve balance. The feedback gain, the
`amount of feedback provided to the subject relative to the
`measured body sway angle and angular velocity, may be
`adjusted by the system operator. The information provided
`on the operator’s display provides an objective measure for
`determining improvements in balance brought about by the
`application of feedback, and by altering feedback gains.
`For visual feedback, a visual feedback system incorpo-
`rated in a pair of lightweight eyewear may be used. An
`imaging system mounted in the eyewearis used to project a
`visual feedback display generated by the system processor
`
`9
`
`9
`
`

`

`5,919,149
`
`5
`into the eye of the wearer of the eyewear. Because the
`viewer’s vision is not otherwise restricted by the eyewear,
`the projected display appears to float in the normal visual
`field of the subject. The subject is thus able to see both the
`world around him andthe display simultaneously. The visual
`feedback display preferably includes a horizontal bar that
`movesin relation to the forward and backward (pitch) and
`left and right (roll) sway of the subject’s upper body. The
`width of the horizontal bar increases or decreases in relation
`to the vectorial combination of the roll and pitch velocities
`of the subject’s upper body. As the subject’s angular sway
`approachesthe subject’s angular cone of stability, a portion
`of the horizontal bar flashes to indicate to the subject that he
`is in dangerof falling. The sensitivity of the movement and
`width of the horizontal bar to the sway angle and sway
`velocity of the subject, as well as the proximity of the
`subject’s sway to the cone of stability necessary for a
`warning to be indicated, are visual
`feedback gain
`parameters, which maybe adjusted by the operator to help
`improve the subject’s control of body sway, and therefore
`improve the subject’s balance control for selected movement
`tasks.
`
`For auditory feedback, the information whichis visually
`displayed when used for visual feedback is presented to the
`subject aurally. Roll and pitch angular displacements of the
`subject may be provided as frequency modulations around
`two different audible tone center frequencies, e.g., 500 Hz
`and 1500 Hz. The velocity of angular sway may be presented
`as an increased or decreased tone volume. A warningthat the
`subject is approaching his cone of stability can be given in
`the form of an audible warning signal that is provided to the
`subject. The depth of frequency modulation, loudness of the
`auditory signals, and conditions for providing the warning
`signal, are auditory feedback gain parameters which may be
`set by the operator to help improve the subject’s control of
`body sway, and therefore improve the subject’s balance
`control for one or more movementtasks.
`
`Tactile feedback may be provided by vibrators that are
`used to convey a senseofrotation of the subject’s torso. For
`example, two vibrators placed on the subject may be used to
`convey a sense of forward and backward sway by modula-
`tion of the frequency of vibration with respect
`to the
`measured sway velocity, and by varying the amplitude of
`vibration with respect to the sway angle. A separate vibrator
`may be used to signal the subject that the sway angle has
`exceeded the limits of safety for the subject. Each of these
`parameters, modulation frequency, amplitude of vibration,
`and the body sway safety limit, is a tactile feedback gain
`parameter that may be adjusted by an operator to improve
`the subject’s control of body sway and therefore improve the
`subject’s balance control for one or more movementtasks.
`Body sway and sway velocity feedback signals may also
`be provided as varying electrical signals which are used to
`directly stimulate the vestibular nerve. Such stimulation is
`sensed by the subject as a change in the angular and/orlinear
`position of the head. Feedback signals for such direct
`electrical stimulation are transmitted transcutaneously to an
`implantable device directly connected via electrodes to the
`close proximity of the vestibular nerve orto the nerveitself.
`The pulse rate, amplitude, and duty cycle of the electrical
`stimulation signal at the electrodes is varied with respect to
`the sway angle and angular velocities that are determined by
`the system processor based on the signals provided by the
`body sway sensors attached to the subject’s upper body. The
`relationship of the signal amplitude, pulse rate, and duty
`cycle to the body sway angles and angular velocity are
`amongthe adjustable feedback gain parametersfor this type
`of feedback.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`Besides providing a more accurate and reliable method
`and apparatus for testing for
`the presence of balance
`disorders, and for providing rehabilitation feedback to
`improve such disorders, the present invention may also be
`used to monitorthe safety of a large number of subjects who
`are in dangeroffalling, as well as for providing a record of
`how and when a subject, for example, in a home for the
`elderly, actually fell.
`In accordance with the present
`invention, a subject’s body sway angle and sway angular
`velocity is measured using light-weight wearable body sway
`sensors that don’t restrict the subject’s movement. Thus,
`continuous subject monitoring may be obtained, and feed-
`back provided, without significantly interferimg with the
`subject’s day-to-day activities. The information provided by
`the wearable body sway sensors may be continuously pro-
`vided to a system processor attached to the subject and
`stored therein for future analysis. Moreover, the body sway
`signals provided by the body sway sensors worn by multiple
`subjects may be provided, via conventional wireless trans-
`mission techniques,
`to a “remote” system processor,
`whereby the safety of a large number of subjects may be
`monitored simultaneously. Such a system may be pro-
`grammed to provide warnings to the operator when one of
`the subjects exceeds a pre-defined body swaysafety limit for
`that subject, indicating that the subject is in dangeroffalling.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic block diagram of an angular position
`and velocity based body sway diagnosis and rehabilitation
`system in accordance with the present invention.
`FIG. 2 is a schematic illustration of a human subject
`wearing body swaysensors that are used to provide body
`sway and angular velocity data in roll and pitch directions,
`and an exemplary visual body sway angle and angular
`velocity feedback device used for providing improved bal-
`ance control in accordance with the present invention.
`FIG. 3 is an illustration of an exemplary operator’s
`display for providing body sway angle and angular velocity
`information to an operator in accordance with the present
`invention.
`
`FIG. 4 is an illustration of an exemplary visual body sway
`angle and angular velocity feedback system in accordance
`with the present invention.
`FIG. 5 is an illustration of an exemplary visual body sway
`angle and angular velocity feedback display in accordance
`with the present invention.
`FIG. 6 is a flow chart illustrating the steps of an exemplary
`system processor control program algorithm for sampling
`body sway sensors, providing an operator’s display, and
`providing visual body sway angle and angular velocity
`feedback in accordance with the present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The present invention provides a method and apparatus
`for significantly improving the specificity, accuracy and
`reliability of non-invasive diagnostic tests for the presence
`of balance and gait disorders. The present invention also
`provides a rehabilitory method and apparatus for improving
`a subject’s balance and gait control. An angular position and
`velocity based body sway diagnostic and rehabilitory system
`for monitoring body sway and for providing body sway
`feedback to a subject to help improve the subject’s control
`of body sway is illustrated generally at 10 in FIG. 1.
`Light-weight wearable body sway sensors 12 are attached to
`
`10
`
`10
`
`

`

`5,919,149
`
`7
`the upper body of a subject and provide body sway signals
`to a system processor 14 which derives body sway angle and
`body sway angular velocity information therefrom. As will
`be discussed in more detail below, various types of body
`sway sensors, including angular velocity transducers, may
`be used to provide body sway signals indicative of the upper
`body motion of a subject to the system processor 14.
`The system processor 14 may be implemented as a
`conventional microprocessor based computer system having
`computer memory 16, an operator’s display unit 18, e.g., a
`standard 14-inch computer display console, a printer or
`plotter 20, and an operator’s input device 22, such as a
`conventional computer keyboard. The processor memory 16
`may include short-term memory, e.g., RAM, as well as
`long-term memory, such as is provided by a conventional
`magnetic disk storage system. The system processor’s
`memory 16 operates in a conventional mannerto store the
`programmedseries of instructions and algorithmsthat con-
`trol operation of the system processor 14 and to store data
`generated by the system processor.
`the system
`invention,
`In accordance with the present
`processor 14 is programmed to transform the body sway
`signals provided by the body sway sensors 12 into useful
`body sway angle and body sway angular velocity informa-
`tion formats. The body sway angle and body sway angular
`velocity information is displayed by the system processor 14
`in the form of an operator’s display that is presented to the
`operator on the operator’s display unit 18. From this for-
`matted information, the system operator, e.g., a physician, is
`able to analyze the body sway of a subject during the
`performanceof various motortasks, to thereby diagnose the
`existence of a balanceorgait deficit. Ahard copy of the body
`sway information provided on the operator’s display unit 18
`may be obtained using the system printer or plotter 20. It
`should be noted that body sway sensors 12 may also be
`attached to other portions of the subject’s body, such as the
`waist, upper leg, or lowerleg, to provide information on the
`motion of these body segments to the system processor 14,
`in addition to the information provided concerning the
`motion of the subject’s trunk. The system processor 14 may
`be programmed to take advantage of this additional body
`motion information. In such a case, the system processor 14
`is programmed as a motion analysis system, whose analysis
`results can be provided to a system operator on the opera-
`tor’s display unit 18. The system processor 14 mayalso be
`programmedto infer trunk angular positions and velocities
`from the information provided by these sensors at other,
`non-trunk, body locations.
`the system
`invention,
`In accordance with the present
`processor 14 mayalso be programmed to provide feedback
`of body sway angle and angular velocity information to a
`subject. As will be discussed in more detail below, body
`sway angle and angular velocity feedback may be provided
`to a subject in visual, auditory, or tactile form, or may be
`provided in the form of a varying electrical signal for
`directly stimulating the vestibular nerve. Visual 24, auditory
`26, tactile 28, and electro-vestibular 30 feedback systems
`may, therefore, be provided in accordance with the present
`invention to deliver body sway angle and angular velocity
`feedback signals provided by