WO1996008197A1

WO1996008197A1 - Fiber optic motion monitor for breath and heartbeat detection and a technique for processing biomedical sensor signals contaminated with body movement noise

Info

Publication number: WO1996008197A1
Application number: PCT/US1995/011051
Authority: WO
Inventors: Roger A. Stern; Eric G. Rawson; Michael Bennett; Jonathan R. Ferris; Charles F. Giese
Original assignee: Alamed Corporation
Priority date: 1994-09-12
Filing date: 1995-09-12
Publication date: 1996-03-21
Also published as: AU3542095A

Abstract

A fiber optic motion monitor includes a light source (21) and an optical fiber waveguide (22) with a sensing section (4) intermediate an input end and an output end. A motion transmitting device (3) is coupled to the sensing section of the optical fiber waveguide for transmitting motion of a patient to the sensing section. A photodetector (23) is positioned to receive a speckle pattern of light which changes in response to movement of the patient and sensing section. The sensing section (4) of the optical fiber waveguide includes a plurality of loops which are positioned between a relatively flexible plate (2) and a resistance member (3) such that the loops will change shape upon movement of the patient due to the patient's breathing and/or heartbeat. Also disclosed is a technique for identifying portions of a modal noise signal that are contaminated by body movement noise and then disregarding these contaminated portions during further processing.

Description

Fiber Optic Motion Monitor for Breath and Heartbeat Detection and a Technique For Processing Biomedical Sensor Signals

Contaminated With Body Movement Noise

BACKGROUND OF THE INVENTION

Cross Reference to Related Applications

This application is a continuation-in-part of U.S. Patent No. 5,436,444, issued July 25, 1995, which is a continuation-in-part of U.S. Patent 5,291,023, issued March 1, 1994, which is a continuation-in-part of U.S. Patent No. 5,212,379 issued May 18, 1993, teachings of which are incorporated herein by reference.

Field of the Invention

This invention relates to an improved fiber optic motion monitor for detecting changes in breathing or heartbeat of a subject, and in particular, small children. This invention relates also to motion monitors for detecting body motions, such as those resulting from respiration and heartbeats, and, more particularly, to optical fiber motion monitors for detecting motion based on modal noise produced by minute motions of an optical fiber.

A significant cause of death in infants (birth to about two years) is "crib death" or sudden infant death syndrome (SIDS). Medical authorities in general agree that some infants simply stop breathing during sleep (apnea) and that death can be prevented if the condition is detected and help is provided within a short time (some 30 to 60 seconds) by trained personnel or parents by using, for example, mouth-to-mouth resuscitation or similar techniques. Apnea monitors already exist but their cost creates an affordability problem that limits their use. Furthermore, the existing monitors produce considerable numbers of false alarms in infants with shallow breathing. Therefore, there has been a need for a breathing and/or heartbeat monitor which is cost efficient and reliable.

Optical fiber motion monitors are disclosed in the above-identified patents for use in detecting apnea, tachycardia, and bradycardia, particularly in infants. Apnea is a condition in which a person simply stops breathing while sleeping, and tachycardia and bradycardia are conditions in which the person's heartbeat rate rises dangerously high or falls dangerously low, respectively. Apnea and bradycardia are a significant cause of death in infants (known as Sudden Infant Death Syndrome or SIDS), which can be prevented if these conditions are detected and help is provided in time.

The above-identified patents disclose optical fiber motion monitors in which a few meters of an optical fiber are embedded in a subject's clothing or in a blanket, mattress cover, or other convenient bedding material. Coherent light is injected into one end of the optical fiber and minute motions of the optical fiber generate changes in the fiber's speckle pattern. These changes are detected as modal noise by a photo- detector that is coupled to the other end of the optical fiber. The speckle pattern has a granular mottled appearance which is created by constructive and destructive interference of light waves that are guided in each of the independent modes or optical paths within the optical fiber. Moving the optical fiber causes minute changes in many of the optical path lengths or causes waves that are guided in one mode to be coupled into another mode, with a resulting change in optical path length. Such changes in optical path length need only be a fraction of a wavelength to substantially alter the resulting speckle pattern. The modal noise signal detected by the photodetector is then processed by respiration and heartbeat detection and processing circuits to extract the subject's respiration and heartbeat rates.

However, when the subject moves, unwanted noise is introduced into the modal noise signal which interferes with the extraction of the respiration and heartbeat rates from the modal noise signal. Accordingly, there has been a need for a technique for preventing this body movement noise from affecting information extracted from the contaminated modal noise signal. The present invention clearly fulfills this need.

Disclosure of the Invention

Accordingly, one object of the present invention is to provide a novel fiber optic motion monitor which is cost effective and reliable.

Another object of the invention is to provide a novel fiber optic motion monitor having an increased sensitivity to body motions and an improved signal-to-noise ratio.

Another object of the invention is to provide a novel fiber optic motion monitor which is less susceptible to non-meaningful motions which might otherwise produce false alarms.

A still further object of die present invention is to provide a novel fiber optic motion monitor which can be shielded from accidental damage and from human fluids or other wastes which might damage the monitor.

A still further object of the present invention is to eliminate the need for relatively long lengths of optic fibers between the electro-optic components and the poπion of the fiber which moves in response to the mechanical motions to be detected, i.e., those caused by the breathing and/or heartbeat of the subject.

Yet another object to be achieved by the present invention is to provide a novel fiber optic motion monitor which employs a mechanical advantage in transferring the motion of a movable member caused by motion of the subject into a magnified motion of the fiber coil used to detect the motion.

It is yet another object of the invention to provide a technique for identifying and eliminating contaminated portions of a modal noise signal.

These and other objects are achieved according to the present invention which includes a light source; an optical fiber waveguide having an input end coupled to die light source, an output end, and a multi-loop sensing coil intermediate the input and output ends; means for transmitting a motion from an object to the sensing coil, including a movable member and a resistance member between which the sensing coil is disposed so that when motion of the object results in movement of the movable member, the loops of the multi-loop sensing coil are pressed against the resistance member and thereby change shape; photodetector means positioned proximate to the output end of the optical fiber waveguide for receiving therefrom a speckle pattern of light, which pattern changes in response to movement of the multi-loop sensing coil, the photodetector means generating electrical signals representative of changes in the speckle patterns; and output means coupled to the photodetector means for producing an ouφut indicative of motion of the object based on the electrical signals generated by the photodetector means. A further aspect of the present invention resides in a technique for identifying portions of a modal noise signal that are contaminated with body movement noise and then disregarding these contaminated portions during further processing of the signal. The technique generates logic signals that indicate whether a subject is moving (SIM), me subject is resting quietly (SRQ), or the subject is out of bed/deceased (SOBD). Normal processing of the modal noise signal, such as extraction of the subject's respiration and heartbeat rates, is suspended while the subject is moving (SIM is true) or the subject is out of bed/ deceased (SOBD is true), and processing is resumed when me subject is resting quietly (SRQ is true).

The logic signals SRQ, SIM and SOBD are generated by a threshold comparator and logic unit using two measured values, the average amplitude of the modal noise signal (AMP) and the amplitude of the high-frequency content of the signal (HFC). The AMP and HFC values are computed by an average amplitude detector and a high- frequency amplitude detector, respectively. In the threshold comparator and logic unit, die amplitude (AMP) and high-frequency content (HFC) values are compared with upper and lower amplitude and high-frequency -content thresholds.

In one preferred technique of the present invention, if the amplitude (AMP) of the modal noise signal is greater than an upper amplitude threshold (UAMPT) and the high-frequency content (HFC) of the modal noise signal is greater than an upper high- frequency-content threshold (UHFCT), the subject is classified as moving (SIM). If d e amplitude (AMP) of the modal noise signal is less than a lower amplitude threshold (LAMPT), the subject is classified as being out of bed/deceased (SOBD). If the amplitude (AMP) of the modal noise signal is between the upper and lower amplitude thresholds, the subject is classified as resting quietly (SRQ).

In another preferred technique of the present invention, which is used when d e high-frequency content (HFC) value is measured by a derivative zero-crossing method, the subject is classified as being out of bed/deceased (SOBD) only if d e amplitude (AMP) of the modal noise signal is less than a lower amplitude threshold (LAMPT) and d e high-frequency content (HFC) of the modal noise signal is greater than a lower high-frequency-content threshold (LHFCT).

A modal noise signal in accordance witii the present invention can also be used to prevent body movement noise from affecting information extracted from other contaminated biomedical sensor signals, such as those generated by EKG and EEG sensor systems and blood oximetry and plethysmographic sensors. The present invention can also be used to monitor patients in a hospital or nursing home to provide patient status at a remote nursing station.

It will be appreciated from die foregoing diat the present invention represents a significant advance in the field of optical fiber motion monitors. Other features and advantages of me present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

Brief Description of the Drawings

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to die following detailed description when considered in connection wilh the accompanying drawings, wherein:

Figure 1 shows a first preferred embodiment according to the present invention illustrating die sensing section of the optical fiber waveguide located between die "^* flexible tympanum constituting the movable member and the relatively rigid bottom plate constituting the resistance member;

Figure 2 illustrates ie basic elements of me invention including the opto- electrical system for detecting motion of the sensing coil of the optical fiber waveguide;

Figure 3 illustrates a front view of d e display device used for displaying the breadiing and/or heart rate of die patient;

Figure 4 illustrates a second preferred embodiment including an intermediate lever attached to a center portion of the tympanum for pivoting against the sensing coil of the optical fiber waveguide;

Figure 5 illustrates a third embodiment according to the present invention including an expandable balloon disposed between die tympanum and a base plate for imparting horizontal displacements to the sensing coil of me optical fiber waveguide; Figure 6A illustrates a fourth embodiment according to die present invention wherein a pneumatic or hydraulic reservoir is provided between he tympanum and a base member for imparting horizontal force to a piston which presses against the sensing coil of die optical fiber waveguide;

Figure 6B illustrates a modification of the fourth embodiment which includes a flexible bellows assembly in place of the piston shown in Figure 4A;

Figure 7 illustrates a fifth embodiment according to me present invention, similar to the second embodiment, but with a 90° rotator device coupled between the sensing coil of the optical fiber waveguide and the end of the lever used to impart movement to d e sensing coil;

Figure 8 illustrates a sixth emhodimenr according to me present invention wherein the sensing coil is positioned horizontally between radially oriented finger projections or, alternatively, attached to the tympanum and d e resistance member, so that the sensing coil at rest follows a path which undulates slightly out of the nominal plane of the sensing coil;

Figure 9 illustrates an assembled side view of the sixth embodiment;

Figure 10 is a block diagram of a preferred embodiment of die present invention;

Figure 11 is a flowchart of one preferred technique of the present invention;

Figure 12 is a flowchart of another preferred technique of the present invention; and

Figure 13 is a block diagram of anoύier preferred embodiment of die present invention.

Best Mode for Carrying Out the Invention

Referring now to die drawings, wherein like numerals designate identical or corresponding parts throughout the several views, and more particularly to Figure 1 diereof, d ere is shown a first embodiment according to die present invention showing me general features of die fiber optic sensor 1 according to the present invention. As shown in Figure 1 , a relatively rigid base plate 3 functions as a resistance member which can be, for example, 16" X 24" and constructed of l/8th inch plywood, for example, supports a similar relatively less rigid top plate as die tympanum plate, at the four corners diereof by four rigid spacers 5. The top plate, or tympanum plate 2, may be die same size as the base plate while of somewhat thinner plywood so as to be more flexible, i.e. , it is desirable to make me center of the top plate more responsive to mechanical movements in a direction normal to die plane of die tympanum plate 2. Alternatively, die tympanum plate 2 could be made from a thin sheet of fiberglass, PLEXIGLASS, resin material, plastic membrane, or a flexible metal plate at a thickness of, for example, l/16th inch. PLEXIGLASS is a trademark owned by Rohm and Haas, which is generally known in the art and comprises a polymediyl methacrylate. As such it is a resin compound and hereafter included in die term resin .

A sensing coil 4 of N turns of a multi-mode optical fiber is positioned between die tympanum plate 2 and base plate 3 in such a position that opposite sides of die coil engage respective ones of die upper and lower plates 2, 3. If multiple loops are used, diey can be fashioned from a single fiber, looped several times, with die light passing sequentially through each loop. The diameters of me loops of die fiber coil constituting the sensing coil 4 are somewhat larger man die space between die two plates, so that die natural flexure of the fibers tends to hold die coil in position between me plates. Alternatively, the coils could be attached to one plate with a small amount of glue, so tiiat die opposite edge of die coil rests widiin a suitable dent provided on die opposite plate. Thus, a small amount of compression is applied to the coil in its resting state, distorting die loops slightly out of perfect circularity. Thus, when die tympanum plate 2 moves up, and down, it decompresses, and further compresses, respectively, die sensing coil 4 along die axis normal to the top and bottom plates. Figure 2 shows die basic opto-electric components of die present invention including laser 21, optical fiber waveguide 22, multi-loop sensing coil 4, photodetector 23 and an output circuit 24 for receiving electrical signals from the photodetector and analyzing the signals to determine information about the breadiing and/or heartbeat of die subject. Movement or bending of die sensing coil 4 causes changes in me speckle pattern output from me output end of die optical fiber waveguide 22 and received by die photodetector 23, as disclosed in me prior patents. The output circuit could be as simple as the amplifier and loudspeaker disclosed in U.S. Patent No. 5,436,444, or in d e more complicated breathing and heartbeat analysis circuits of U.S. Patent No. 5,291,013. In particular, d e different photodetector embodiments, the processing techniques and/or the output circuits of die cross-referenced prior applications can be utilized in the present invention.

As also shown in Figure 2, a display device 27 is connected to d e output circuit 24 for receiving information output to me display device in order to display die detected changes in d e breath rate and heart rate of d e patient. The fiber optic sensor 1 would not require d e attachment of sensors to the patient being monitored. The display device 27 may be located adjacent to die patient's bed, thereby providing quick assessment of die current status of die patient's breath rate and/or heart rate. Optionally, d e recent history of heart rate and bread ing of die patient could also be displayed, mereby improving the accuracy of me assessment of die patient's condition and reduction in die time necessary for an operator to perform the routine measurements on the patients. According to die invention, me average heart rate and average breath rate are calculated using me teachings of the prior cross-referenced applications, notably d ose of U.S. Patent No. 5,291,013. The averaging is performed for die most recent time interval of appropriate predetermined duration. For example, a preferable duration for heart rate averaging would be 5-20 seconds, and a preferable duration for breath rate averaging would be 0.5-20 minutes. These time intervals could be preset by die healthcare professional to any convenient and appropriate values desired. The average value of heart rate and bream rate are displayed in a conveniently sized display box, advantageously a back lit liquid crystal display (LCD) unit, showing die current average values and updating diem periodically (for example, every second, or every few seconds, etc.). In this manner, the care giver can see immediately upon entering die patient's room what the current average breath and heart rates are. Furthermore, since me values displayed represent averages over a longer time period than a care giver (typically die ward nurse) can normally allow to each patient, the measurements will be more accurately representative of me patient's true status. Finally, because me care giver does not need to awaken or odierwise disturb me patient, the heart rate and bream rate values they record for the patient are free from distortions due to intervention by die care giver.

In a preferred embodiment, a portion of the LCD display would present a graph of die recent history of eidier or bodi of die heart rate and bread rate. In is manner, past readings over an extended time period (for example, one hour, several hours, etc.) would be displayed as an analog graph on separate areas of die LCD display. Thus, die care giver would have at his disposal not only me current value, but would also be able to observe die current history which would indicate whedier mere had been any unusual perturbations, possibly short-lived, in the period since me patient had been last observed. It will be understood by diose skilled in die art that numerous variations of die above teachings of die display device are possible. For example, the device could be connected to die existing data monitoring network in the hospital or nursing home and die data could dius be stored in a permanent data file. Anod er preferred embodiment would include alarm capabilities, sounding an alarm locally or at an adjacent nursing station, if apneas of longer than a preset during (for example, 20 or 30 seconds) occur, or if heart rates exceeded or subseded preset rate diresholds, as described in die cross-referenced applications. Or, in order to prevent anxiety in die patient by having a continuous local read-out of his/her breadi rate and heart rate, die wall-mounted LCD display could feature a sensor (an IR optical detector, for example) which would allow die care giver to switch die display on when die care giver enters die room, using a convenient hand-held or lapel mounted IR emitter device. Figure 3 shows one example of a design for die LCD display device 27, showing the bream rate and heart rate over a predetermined period of time. It should also be noted that the LCD display can be applied to the monitoring devices of prior U.S. Patent No. 5,436,444, 5,291,023 and 5,212,379.

As illustrated in Figure 4, a second embodiment according to the present invention includes an intermediate lever 7 attached to a center portion of die tympanum plate 2 which pivots at a pivoting point connected to fulcrum 6. An end of me lever 7 which contacts sensing coil 4 of die optical fiber waveguide imparts vertical force to the sensing coil 4 at a first side thereof , while the opposite side of me sensing coil 4 engages base plate 3. In Figure 4, die lever 7 is positioned relative to die fulcrum 6 such diat die short lever arm is displaced vertically by motions of the tympanum plate 2. The end of die long lever arm is attached to peripheral portions of me loops constituting me sensing coil 4. This results in fiber motions which are amplified by me mechanical advantage of die lever 7. Mechanical advantages in the range of 3 X to 10X are practical, and would yield a corresponding increase in sensitivity to vertical motions of the tympanum plate 2. With such a construction, die vertical movements imparted to die tympanum plate 2 are magnified by d e vertical pressing force imparted at die sensing coil 4 of me optical fiber waveguide. The fiber sensing coil 4 could advantageously be attached to eid er me lever 7 or the base plate 3 with a small amount of glue or cement, and rest within a detent on me opposite contact point. To assure contact, the coil 4 could advantageously be slightly compressed in its resting state between lever 7 and base plate 3.

Anodier embodiment according to the present invention is illustrated in Figure 5, which shows an expandable balloon 8 located between die tympanum plate 2 and die base plate 3. Upon vertical motions of the tympanum plate 2, the expandable balloon 8 expands or shrinks in the horizontal direction thus imparting horizontal forces to the sensing coil 4 of d e optical fiber waveguide. As shown, d e opposite side of the sensing coil 4 of the optical fiber waveguide engages die resistance member 9. In this manner, the vertical motions due to breathing and heartbeat are translated into horizontal forces to be imparted to e sensing coil 4 of me optical fiber. Vertical motions of the tympanum plate 2 result in corresponding radial motions parallel to me planes of the plates at its horizontal periphery. One edge of die peripheral sides of one or more loops can be attached to ύiis peripheral rim of the expandable balloon, and die opposite peripheral sides of the loop(s) can be attached to die resistance member 9. Thus vertical motions of the tympanum plate 2 will pneumatically flex me fiber loop or loops. Because of the large area of the expandable balloon in contract with the tympanum plate 2, there is a pneumatic magnification of the displacement of the fiber loop or loops. Additional resistance members 9 A can be positioned about diree sides of me balloon to constrain nearly all of its horizontal motion to occur near the fiber sensor loop attachment point.

As shown in Figure 6A, the expandable balloon 8 can be replaced by a pneumatic or hydraulic reservoir 11 which serves to impart horizontal motion to a piston 10 coupled between the reservoir 11 and die sensing coil 4 of the optical fiber waveguide. The resistance member 9 is provided in a similar location as shown in Figure 3 described above. The displacement of me piston is magnified over diat of die tympanum plate 2 by the ratio of the cross-sectional area of die reservoir to the cross- sectional area of die reservoir to die cross-sectional area of die piston 10. In diis manner, a mechanical advantage of up to several hundred magnification units can be achieved. The piston drives one rim of a fiber coil, the opposite rim being anchored to die resistance member 9. As shown in Figure 6B, die piston 10 of Figure 6A can be replaced widi a flexible bellows device 10A.

When using a lever system, it is advantageous to convert the motion from the vertical axis to a horizontal axis. This permits a fiber coil with a large diameter to be used, avoiding excessive thickness of me sensor system while at the same time avoiding the coiling of fiber loops into such a small diameter that the fiber is put into an undesirable state of stress due to a high degree of bending, as shown in Figure 4. Anomer way diis can be achieved is illustrated in Figure 7, where a lever, advantageously one widi mechanical advantage, rotates a 90° rotating bracket 12. Rotation of this bracket about its pivot point 13 translates the vertical motion into a corresponding horizontal motion. This motion can men be imparted to die sensing coil 4 of e optical fiber waveguide which is coupled to the 90° rotating bracket 12.

As show in Figures 8 and 9, a sixth embodiment according to die present invention utilizes changes in bending of the sensing coil 4 which is disposed between die upper and lower plates 2, 3 and more specifically between radially extending finger projections 15 which extend from the inner surfaces of die plates 2, 3. As shown in Figure 8 in an exploded view, die sensing coil 4 is positioned horizontally between die radially oriented fingers. It is additionally pointed out that the sensing coil could be attached to me upper plate 2 and die lower plate 3 (which functions as the resistance member) such that die sensing coil 4 at rest follows a padi which undulates slightly out of e nominal plane of the sensing coil, as can be seen in Figure 9. It should also be noted diat die orthogonal projections of me fingers 15 on the top and bottom plates 2, 3 do not overlap, i.e., die fingers of the top and bottom plates are angularly offset in order to provide a desirable degree of undulation of die sensing coil out of its natural plane when die sensor is assembled and in its resting state.

Figure 9 illustrates an assembled side view of die sixtii embodiment which illustrates the manner by which die horizontal coil is pressed in up and down directions by die radially extending fingers. Small vertical motions of me upper plate 2 upwards and downwards cause d e fiber undulation bending to decrease and increase, respectively. While Figures 8 and 9 illustrate only eight radial fingers for simplicity, the overall sensitivity can be increased by using more fingers with tens, hundreds or even thousands of fingers being suitable.

In each of die embodiments shown in Figures 1-9, the upper and lower plates 2, 3 may be provided widi die plurality of rigid spacers 5 located near die corners or edges of die plates in order to hold the two plates a fixed distance apart at their edges,

The resulting changes in compression of me sensing coil 4 of Figures 1 and 4-7, or die changes in bending in Figures 8 and 9, introduces modal noise into the coherent light guided into d e fiber coil, as described in d e previous patent applications noted above. If d e sensor elements 2, 3 and 4 are positioned beneatfi mattress 26 on which a subject is lying, d s modal noise signal can be analyzed to extract information on e breathing and/or heartbeat of die subject, also as disclosed in die above-noted prior applications. It should also be noted d at any of die electro-optical schemes disclosed in d e prior applications can be used wid die structures according to d e present invention.

An advantage of die invention is diat die sensitivity to vibration of die tympanum plate 2 is proportional to N, me number of loops in e fiber coil sensing coil 4, and diis number can advantageously be made quite large; values of N on order of 10, 100, or even 1000, or possibly more, are practical, the optimal number N being selected to provide an appropriate balance between manufac ring complexity and materials cost on me one hand and sensitivity to mechanical motions of the tympanum on the other.

A further advantage of this invention is that me optical fiber waveguide is sheltered from non-meaningful motions because of me relative rigidity of die plates with regard to any motions (for example, shear motions) other than vertical motions of me tympanum center, as compared to tine sensor pad of the above-noted applications. Since the fiber loop sensing coil 4 is compressed only in response to the normal lowest order vibration mode of die tympanum plate 2, it is relatively insensitive to motions along the odier two axes. This improves the signal-to-noise ratio in die modal noise signal, since there will be less extraneous and irrelevant components in the modal noise signal which tend to obscure diose components due to die vertical flexing motions of the tympanum plate 2 associated wid breathing and heartbeat.

A further advantage of the present invention is that die fiber optic motion monitor can be located beneath die mattress, shielding it from accidental damage and from human fluids or odier wastes which might damage the monitor if located on a pad above the mattress.

Yet a further advantage of me present invention is that the electro-optical components (the diode laser and die photodetector) can be located between the upper and lower plates and adjacent to die sensing coil of the optical fiber waveguide, eliminating the use of long fiber lead lengdis between die electro-optical components and me portions of the fiber diat actually move in response to me mechanical motions to be detected, i.e. , diose due to breathing and heartbeat.

A still further advantage of die present invention is diat die sensitivity can be further improved by creating a mechanical advantage in translating die vertical flexural motion of die tympanum plate 2 into a magnified motion of the sensing coil of the optical fiber waveguide. Systems to achieve diis can use die principles of levers, pneumatic systems or hydraulic systems.

As shown in the Figures 10 to 13 for purposes of illustration, one aspect of me present invention is embodied in a technique for identifying portions of a modal noise signal diat are contaminated widi body movement noise and dien disregarding diese contaminated portions during further processing of die signal. The technique generates logic signals diat indicate whether a subject is moving (SIM), the subject is resting quietly (SRQ), or die subject is out of bed/deceased (SOBD). Normal processing of the modal noise signal, such as extraction of the subject's respiration and heartbeat rates, is suspended while die subject is moving (SIM is true) or die subject is out of bed/deceased (SOBD is true), and processing is resumed when die subject is resting quietly (SRQ is true). As shown in Figure 10, an optical fiber motion monitor 30 in accordance widi die present invention includes an optical fiber sensor pad 32 having a few meters of a multi mode optical fiber 34 embedded in die sensor pad, a coherent light source 36 such as an injection laser diode coupled to one end of die optical fiber 34 for injecting coherent light into the optical fiber, and a photodetector/amplifier/filter 38 for detecting, amplifying and filtering a modal noise signal produced by minute motions of the multi mode optical fiber 34. The amplified and filtered modal noise signal is dien digitized by an A/D converter 50 and applied to a respiration detection and processing circuit 52 and a heartbeat detection and processing circuit 54 for extraction of respiration and heartbeat rates, respectively, from the modal noise signal. A pair of AND gates 56 allows d e digitized modal noise signal to be applied to d e processing circuits 52, 54 only when d e subject is resting quietly (SRQ is true). Breath display and alarm unit 58 and heart display and alarm unit 60 provide displays for die respiration and heartbeat rates, respectively, and generate appropriate alarms if these rates fall outside predetermined ranges. Further details of this portion of die invention are set forth in die above-identified patents, which are hereby incorporated by refer¬ ence.

The logic signals SRQ, SIM and SOBD are generated by a threshold comparator and logic unit 62 using two measured values, the average amplitude of the modal noise signal (AMP) and die amplitude of the high-frequency content of me signal (HFC). The AMP and HFC values are computed by an average amplitude detector 64 and a high- frequency amplitude detector 66, respectively. In d e threshold comparator and logic unit 62, die amplitude (AMP) and high-frequency content (HFC) values are compared widi upper and lower amplitude and high-frequency-content diresholds.

In one preferred technique of the present invention, as shown in the flowchart in Figure 11, if the amplitude (AMP) of die modal noise signal is greater dian an upper amplitude direshold (UAMPT) and die high-frequency content (HFC) of die modal noise signal is greater man an upper high-frequency -content direshold (UHFCT), die subject is classified as moving (SIM). If me amplitude (AMP) of me modal noise signal is less than a lower amplitude direshold (LAMPT), die subject is classified as being out of bed/deceased (SOBD). If die amplitude (AMP) of die modal noise signal is between the upper and lower amplitude thresholds, die subject is classified as resting quietly (SRQ).

In another preferred technique of die present invention, as shown in die flowchart in Figure 12, me subject is classified as being out of bed/deceased (SOBD) only if die amplimde (AMP) of die modal noise signal is less dian a lower amplitude threshold (LAMPT) and die high-frequency content (HFC) of die modal noise signal is greater dian a lower high-frequency-content direshold (LHFCT). This technique provides enhanced status detection when die high-frequency content (HFC) value is measured by a derivative zero-crossing method described below.

The amplimde (AMP) and high-frequency content (HFC) values can be measured by many different methods. The amplitude (AMP) of die modal noise signal is a measure of die average amplimde of me raw or unprocessed modal noise signal. A first method of measuring average amplitude involves measuring the minimum and maximum amplitudes of die modal noise signal over some sampling period and dien taking die difference between the two values. This computation, which is actually a peak-to-peak amplimde computation, provides a reasonably good approximation of the average amplimde of the noise signal. A second and more accurate method of measuring average amplimde involves computing an RMS deviation of die modal noise signal* from its mean value. Other methods of measuring die amplitude (AMP) value will be obvious to one skilled in die art.

The high-frequency content (HFC) of die modal noise signal is a measure of the amplimde of die high-frequency content of die raw or unprocessed modal noise signal. A first method of measuring die amplimde of die high-frequency content involves counting me number of zero crossings or sign reversals of die first derivative of die noise signal over some sampling period. The technique shown in Figure 12, using die lower high-frequency-content direshold (LHFCT) along widi die lower amplimde direshold (LAMPT) to classify die subject as being out of bed or deceased (SOBD), is preferred when diis method is used. A second method of measuring me amplimde of the high-frequency content involves counting me number of zero crossings of me noise signal (not its derivative) over some sampling period. This method is simpler than me first method, but is not as accurate. A diird and more accurate method of measuring die amplimde of die high-frequency content involves filtering die modal noise signal wid a high-pass or band pass filter to remove the low-frequency components of me signal. This high-frequency -component signal is men rectified and filtered widi a low- pass filter. The resulting signal provides the equivalent of an envelope following of die high-frequency-component signal. A fourth and even more accurate method of measuring die amplimde of die high-frequency content is to measure me spectral content of d e noise signal directly using any suitable fast Fourier transform (FFT). Other methods of measuring me high-frequency content (HFC) value will be obvious to one skilled in d e art.

Depending on die type of optical fiber 34 used, predetermined direshold values can be programmed into me motion monitor at me time of manufacture if variations in optical fiber response from one monitor to another are small, or customized direshold values can be programmed into me motion monitor after me device is tested if variations in optical fiber response are large.

A sampling rate of 400 Hz and a sampling period of 0.33 sec. were found by way of experiment to be suitable to provide accurate subject status. When die modal noise signal is used to determine respiration and heartbeat rates, contaminated modal noise data is preferably disregarded when SIM is true for an integral number of periods of die rate being sensed using a measure of diat rate as most recentiy determined by me motion monitor. For example, if the heartbeat rate was most recently measured to be 60 beats per minute and SIM becomes true, the incoming modal noise signal is men ignored for as long as SIM remains true, but rounded up to die next integral number of heartbeat periods (heartbeat period = l/(heartbeat rate x 60). In diis manner, die periodicity of d e modal noise signal will be minimally perturbed by disregarding a block of contaminated data samples.

As shown in Figure 13, a modal noise signal in accordance widi die present invention can also be used to prevent body movement noise from affecting information extracted from other contaminated biomedical sensor signals, such as diose generated by EKG and EEG sensor systems and blood oximetry and plethysmographic sensors. This preferred embodiment of me present invention includes a biomedical sensor 70, an A/D converter 72 for digitizing die sensor signal, an AND gate 74 having die digitized sensor signal and the SRQ logic signal as inputs, and an information extraction circuit 76. Normal processing of die biomedical sensor signal for extraction of information is suspended while the subject is moving (SIM is true) or die subject is out of bed/deceased (SOBD is true), and processing is resumed when die subject is resting quietly (SRQ is true). The present invention can also be used to monitor patients in a hospital or nursing home to provide patient status to a remote nursing station.

Although die present invention has been described as implemented in digital form, the invention can be implemented in analog form using comparators and other analog elements, and omitting me A/D converters 50, 72. Furthermore, the techniques described widi respect to Figures 10 to 13 are not to be read as being limited in application to die embodiments illustrated in Figures 1 to 9.

From the foregoing, it will be appreciated diat the present invention represents a significant advance in die field of optical fiber motion monitors. Although several preferred embodiments of the invention have been shown and described, it will be apparent diat odier adaptations and modifications can be made widiout departing from the spirit and scope of die invention. Accordingly, die invention is not to be limited, except as by die following claims.

Obviously, numerous modifications and variations of die present invention are possible in light of die above teachings. It is therefore to be understood diat widiin the scope of the appended claims, the invention may be practiced odierwise dian and specifically described herein.

Claims

1. A fiber optic body motion monitor comprising: a light source; an optical fiber waveguide including an input end, an output end, and a sensing section intermediate said input and output ends, said optical fiber being positioned to receive light from said light source at said input end; means, coupled to said sensing section, for transmitting motion of a subject being monitored to at least a portion of said sensing section so as to exert a force on said portion of said sensing section; photodetector means positioned proximate to said output end for receiving a speckle pattern of light dierefrom, which pattern changes in response to the force exerted on said sensing section, said photodetector means generating electrical signals representative of changes in said speckle pattern; and means for identifying electrical signals indicative of at least one of breaming motion and heartbeat motion, wherein the sensing section comprises a multi-loop sensing coil.

2. The fiber optic motion monitor according to Claim 1 , wherein said sensing section comprises: a multi-loop sensing coil.

3. The fiber optic motion monitor according to Claim 1, wherein said means for transmitting motion from said subject to said sensing coil includes a movable member for supporting said subject and causing said sensing coil to deform.

4. The fiber optic motion monitor according to Claim 3, further comprising: a resistance member mounted opposite d e movable member for contacting an abutting portion of said sensing coil to resist translational movement of the abutting portion of said sensing coil so that me loops thereof change shape when said movable member exerts a force on said sensing coil.

5. The fiber optic motion monitor according to Claim 4, wherein said resistance member comprises a base plate and said movable member comprises a flexible top plate.

6. The fiber optic motion monitor according to Claim 4, further comprising: mechanical amplification means located between said movable member and said sensing coil for magnifying motions imparted to the movable member by motion of die subject and for transferring magnified motions to said sensing coil.

7. The fiber optic motion monitor according to Claim 6, wherein said mechanical amplification means comprises: a fulcrum; and a lever connected to said movable member and located between said movable member and said resistance member for pivoting on said fulcrum at a first location of the lever and contacting peripheral portions of die loops of said sensing coil at a second location of die lever so that said lever moves against the loops of die sensing coil and changes the shapes of die loops upon movement of said movable member.

8. The fiber optic motion monitor according to Claim 7, wherein said mechanical amplification means comprises a 90° rotator coupled between said second location on said lever and said peripheral portions of die loops of said sensing coil.

9. The fiber optic motion monitor according to Claim 7 or 8, wherein said lever comprises a first end attached to a center portion of said movable member and a second end abutting against said peripheral portions of d e loops of said sensing coil.

10. The fiber optic motion monitor according to Claim 6, wherein said mechanical amplification means comprises: an expandable balloon located between said movable member and said resistance member and contacting peripheral portions of die loops of said sensing coil.

11. The fiber optic motion monitor according to Claim 10, further comprising: lateral constraining members positioned to define a constraining housing widi said movable member and said resistance member, the constraining housing having an open end adjacent to said sensing coil.

12. The fiber optic motion monitor according to Claim 6, wherein said mechanical amplification means comprises: a pneumatic or hydraulic reservoir located between said movable member and said resistance member; and a piston coupled between said reservoir and said loops of die sensing coil.

13. The fiber optic motion monitor according to Claim 3, further comprising: a resistance member including a plurality of finger portions which extend from a surface diereof to contact said sensing coil; and said movable member also including a plurality of fmger portions which also extend from a surface thereof to contact said sensing coil.

14. The fiber optic motion monitor according to Claim 13, wherein orthogonal projections of said finger portions extending from said movable member do not overlap orthogonal projections of said finger portions extending from said resistance member.

15. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a flexible PLEXIGLASS plate.

16. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a flexible resin plate.

17. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a flexible plywood plate.

18. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a flexible fiberglass plate.

19. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a flexible metal plate.

20. The fiber optic motion monitor according to Claim 3, wherein said movable member comprises a plastic membrane.

21. The fiber optic motion monitor according to Claim 3, wherein said movable member directly contacts said loops of me sensing coil upon movement of said subject.

22. The fiber optic motion monitor according to Claim 5 or 7, further comprising: a plurality of rigid spacers which couple said movable member to said resistance member and mainatain said movable member and said resistance member in spaced apart relationship to each odier.

23. The fiber optic motion monitor according to Claim 10 or 12, further comprising: a base plate; and a plurality of rigid spacers which couple said movable member to said base plate.

24. The fiber optic motion monitor according to Claim 22, wherein me loops of die sensing coil define spaced apart opposed portions, and wherein die distance between the opposed portions of the loops of die sensing coil is approximately equal to die spacing between die movable member and the resistance member, and the opposed portions of die loops of said sensing coil are attached to at least one of said movable member and said resistance member.

25. The fiber optic motion monitor according to Claim 22, wherein said photodetector means and die means for identifying said electrical signals are located between said movable member and said resistance member.

26. The fiber optic motion monitor according to Claim 1, further comprising: display means for displaying at least one of a breadiing rate and heart rate of said subject.

27. The fiber optic motion monitor according to Claim 1 , comprising: means for determining at least one of an average breathing rate and an average heart rate of said subject; and means for displaying at least one of die determined average breadiing rate and die average heart rate.

28. The fiber optic motion monitor according to Claim 26, wherein said display means comprises: means for displaying a graph indicative of one of said average breadiing and heart rate over a predetermined time period.

29. The fiber optic motion monitor according to Claim 26, 27 or 28, wherein said display means comprises an LCD display unit.

30. The fiber optic motion monitor according to Claim 26, 27 or 28, further comprising: means for determining whemer said identified signals are in an abnormal range; and alarm means for outputting an alarm signal upon a determination that said electrical signals are in said abnormal range.

31. A method for preventing body movement noise from affecting infor¬ mation extracted from a contaminated modal noise signal, comprising the steps of: identifying portions of die modal noise signal diat are contaminated widi body movement noise; and disregarding die contaminated portions of d e modal noise signal during further processing of the signal for extraction of the information.

32. The method as set forth in Claim 31, wherein the step of identifying includes die step of generating logic signals mat indicate whedier a subject is moving (SIM), die subject is resting quietly (SRQ), or me subject is out of bed/ deceased (SOBD) and die step of disregarding includes die steps of suspending processing of die modal noise signal while die subject is moving (SIM is true) or die subject is out of bed/deceased (SOBD is true) and resuming processing when die subject is resting quietly (SRQ is true).

33. The method as set forth in Claim 32, wherein die step of generating logic signals includes die steps of: measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); classifying die subject as moving (SIM) if the amplimde (AMP) of d e modal noise signal is greater dian an upper amplitude direshold (UAMPT) and die high- frequency content (HFC) of die modal noise signal is greater dian an upper high- frequency-content threshold (UHFCT); classifying d e subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT); and classifying die subject as resting quietiy (SRQ) if die amplimde (AMP) of d e modal noise signal is between die upper and lower amplimde diresholds.

34. The method as set forth in Claim 32, wherein die step of generating logic signals includes die steps of: measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); classifying me subject as moving (SIM) if me amplimde (AMP) of die modal noise signal is greater dian an upper amplimde direshold (UAMPT) and die high- frequency content (HFC) of die modal noise signal is greater dian an upper high- frequency-content direshold (UHFCT); classifying the subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT) and die high-frequency content (HFC) of die modal noise signal is greater than a lower high-frequency-content direshold (LHFCT); and classifying die subject as resting quietly (SRQ) if die amplimde (AMP) of die modal noise signal is between die upper and lower amplimde diresholds.

35. A med od for preventing body movement noise from affecting infor¬ mation extracted from a biomedical sensor signal, comprising me steps of: identifying portions of a modal noise signal diat are contaminated widi body movement noise; and disregarding corresponding contaminated portions of die biomedical sensor signal during further processing of die sensor signal for extraction of die information.

36. The method as set forth in Claim 35, wherein me step of identifying includes die step of generating logic signals diat indicate whetiier a subject is moving (SIM), the subject is resting quietly (SRQ), or die subject is out of bed/ deceased (SOBD) and die step of disregarding includes die steps of suspending processing of the biomedical sensor signal while the subject is moving (SIM is true) or die subject is out of bed/deceased (SOBD is true) and resuming processing when the subject is resting quietly (SRQ is true).

37. The mediod as set forth in Claim 36, wherein the step of generating logic signals includes die steps of: measuring an average amplimde of the modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); classifying the subject as moving (SIM) if die amplimde (AMP) of die modal noise signal is greater dian an upper amplimde direshold (UAMPT) and d e high- frequency content (HFC) of die modal noise signal is greater dian an upper high- frequency-content threshold (UHFCT); classifying the subject as being out of bed deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT); and classifying die subject as resting quietly (SRQ) if die amplimde (AMP) of die modal noise signal is between die upper and lower amplimde thresholds.

38. The method as set forth in Claim 36, wherein e step of generating logic signals includes die steps of: measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); classifying me subject as moving (SIM) if me amplimde (AMP) of die modal noise signal is greater dian an upper amplimde direshold (UAMPT) and d e high- frequency content (HFC) of the modal noise signal is greater dian an upper high- frequency-content direshold (UHFCT); classifying die subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT) and the high-frequency content (HFC) of die modal noise signal is greater dian a lower high-frequency-content direshold (LHFCT); and classifying die subject as resting quietiy (SRQ) if the amplimde (AMP) of me modal noise signal is between die upper and lower amplimde thresholds.

39. Apparatus for preventing body movement noise from affecting information extracted from a contaminated modal noise signal, comprising: means for identifying portions of the modal noise signal d at are contaminated widi body movement noise; and means for disregarding die contaminated portions during further processing of the signal for extraction of die information.

40. The apparatus as set forth in Claim 39, wherein me means for identifying includes means for generating logic signals diat indicate whether a subject is moving (SIM), the subject is resting quietly (SRQ), or the subject is out of bed/deceased (SOBD) and the means for disregarding includes means for suspending processing of die modal noise signal while die subject is moving (SIM is due) or die subject is out of bed/deceased (SOBD is true) and means for resuming processing when me subject is resting quietly (SRQ is true).

41. The apparatus as set forth in Claim 40, wherein die means for generating logic signals includes: means for measuring an average amplimde of the modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); means for classifying the subject as moving (SIM) if die amplimde (AMP) of the modal noise signal is greater dian an upper amplimde direshold (UAMPT) and the high-frequency content (HFC) of the modal noise signal is greater dian an upper high- frequency-content direshold (UHFCT); means for classifying die subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT); and means for classifying die subject as resting quietly (SRQ) if die amplimde (AMP) of die modal noise signal is between die upper and lower amplimde diresholds. ^• 42. The apparatus as set forth in Claim 40, wherein the means for generating logic signals includes: means for measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); means for classifying the subject as moving (SIM) if die amplimde (AMP) of the modal noise signal is greater dian an upper amplimde direshold (UAMPT) and die high-frequency content (HFC) of die modal noise signal is greater dian an upper high- frequency-content direshold (UHFCT); means for classifying die subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT) and the high-frequency content (HFC) of die modal noise signal is greater dian a lower high-frequency-content direshold (LHFCT); and means for classifying die subject as resting quietly (SRQ) if die amplimde

(AMP) of die modal noise signal is between die upper and lower amplimde diresholds.

43. Apparatus for preventing body movement noise from affecting information extracted from a biomedical sensor signal, comprising: means for identifying portions of a modal noise signal diat are contaminated widi body movement noise; and means for disregarding corresponding contaminated portions of d e biomedical sensor signal during further processing of die sensor signal for extraction of die infor¬ mation.

44. The apparatus as set forth in Claim 43, wherein die means for identifying includes means for generating logic signals diat indicate whetiier a subject is moving (SIM), die subject is resting quietly (SRQ), or die subject is out of bed/deceased (SOBD) and die means for disregarding includes means for suspending processing of die sensor signal while die subject is moving (SIM is true) or die subject is out of bed/deceased (SOBD is true) and means for resuming processing when me subject is resting quiedy (SRQ is true).

45. The apparatus as set forth in Claim 44, wherein die means for generating logic signals includes: means for measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); means for classifying the subject as moving (SIM) if die amplitude (AMP) of die modal noise signal is greater d an an upper amplimde direshold (UAMPT) and die high-frequency content (HFC) of d e modal noise signal is greater dian an upper high- frequency-content direshold (UHFCT); means for classifying die subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT); and means for classifying the subject as resting quietly (SRQ) if d e amplimde (AMP) of die modal noise signal is between die upper and lower amplimde diresholds.

46. The apparatus as set forth in Claim 44, wherein die means for generating logic signals includes: means for measuring an average amplimde of die modal noise signal (AMP) and an amplimde of die high-frequency content of die modal noise signal (HFC); means for classifying die subject as moving (SIM) if die amplimde (AMP) of die modal noise signal is greater dian an upper amplimde direshold (UAMPT) and die high-frequency content (HFC) of die modal noise signal is greater dian an upper high- frequency-content threshold (UHFCT); means for classifying die subject as being out of bed/deceased (SOBD) if die amplimde (AMP) of die modal noise signal is less dian a lower amplimde direshold (LAMPT) and die high-frequency content (HFC) of die modal noise signal is greater dian a lower high-frequency-content direshold (LHFCT); arid means for classifying die subject as resting quietly (SRQ) if die amplimde (AMP) of die modal noise signal is between die upper and lower amplimde diresholds.

47. An optical fiber motion monitor for monitoring motion of a subject, comprising: an optical fiber embedded in a sensor pad, die sensor pad transmitting motion of the subject to die optical fiber; a coherent light source coupled to one end of die optical fiber for injecting coherent light into die optical fiber; a photodetector coupled to the odier end of die optical fiber for detecting modal noise produced by minute motions of die optical fiber; a respiration detection and processing circuit for extracting respiration rate from the modal noise signal; a heartbeat detection and processing circuit for extracting heartbeat rate from the modal noise signal; means for identifying portions of the modal noise signal that are contaminated wid body movement noise; and means for disregarding die contaminated portions of die modal noise signal during processing of die signal by die respiration and heartbeat rate detection and pro¬ cessing circuits.

48. The optical fiber motion monitor as set forth in Claim 47, wherein die contaminated portions of the modal noise signal are disregarded for an integral number of periods of die heartbeat rate using a measure of the heartbeat rate as most recendy determined by die heartbeat detection and processing circuit.

49. The optical fiber motion monitor as set forth in Claim 47, wherein the contaminated portions of die modal noise signal are disregarded for an integral number of periods of die respiration rate using a measure of the respiration rate as most recently determined by die respiration detection and processing circuit.

50. Apparatus for preventing body movement noise from affecting infor¬ mation extracted from a biomedical sensor signal, comprising: an optical fiber embedded in a sensor pad, the sensor pad transmitting motion of a subject to die optical fiber; a coherent light source coupled to one end of die optical fiber for injecting coherent light into die optical fiber; a photodetector coupled to die odier end of die optical fiber for detecting modal noise produced by minute motions of the optical fiber; an information extraction circuit for extracting information from the biomedical sensor signal; means for identifying portions of die modal noise signal diat are contaminated widi body movement noise; and means for disregarding corresponding contaminated portions of the biomedical sensor signal during processing of die sensor signal by die information extraction circuit.

51. The apparatus as set forth in Claim 50, wherein the contaminated portions of d e biomedical sensor signal are disregarded for an integral number of periods of any information extracted from die sensor signal using a measure of die information as most recently determined by die information extraction circuit.