Activity monitoring apparatus with configurable filters

I claim:

1. An activity monitor responsive to body motion for detecting and recording the occurrence of predetermined body movements in a human subject wherein each said predetermined body movement has a characteristic frequency spectrum, said activity monitor comprising: a motion detector for producing a detector output signal in response to body movements of the subject; highpass filter means for attenuating the spectrum of said detector output signal below a predetermined lower threshold frequency; lowpass filter means for attenuating the spectrum of said detector output signal above a predetermined upper threshold frequency; said detector output signal being filtered by said highpass and lowpass filter means whereby the spectrum of said signal corresponds to the characteristic frequency spectrum of the predetermined body movement; memory means of finite capacity; conversion means for sampling said detector output signal and storing the resulting sample signals in said memory means; said upper threshold frequency and said lower threshold frequency each being configurable in response to an applied configuration control signal; and said activity monitor further including a processor circuit having a plurality of selectable operating modes, each mode corresponding to at least one said predetermined body movement, said processor circuit applying configuraton control signals to each said filter means to obtain a frequency spectrum in said detector output signal corresponding to the characteristic frequency spectrum of the predetermined body movement selected by selection of a said operating mode.

2. An activity monitor as defined in claim 1, wherein said processor circuit includes a resident operating program for controlling the configuration of said filter circuits.

3. An activity monitor as defined in claim 2 wherein the monitor includes a data port, and said resident program is changeable through said data port.

4. An activity monitor as defined in claim 2 wherein said resident program is changeable in response to said sampled signals.

5. An activity monitor as defined in claim 1, wherein each said filter means includes an analog switch device responsive to said applied configuration control signal for controlling its respective threshold frequency.

6. An activity monitor as defined in claim 1 including saturation inhibit means responsive to said filtered detector output signal for inhibiting the storing of said output signal in the event said signal exceeds a predetermined threshold level.

7. An activity monitor as defined in claim 1, wherein said monitor includes amplifier means for amplifying said detector output signal, said amplifier having an adjustable amplification factor such that the amplitude of said output signal is within a predetermined range of amplitudes characteristic of said predetermined body movement being monitored.

8. An activity monitor as defined in claim 7, wherein said amplifier has an amplification factor dependent on an applied control signal, and the monitor includes a processor circuit having a plurality of operating modes corresponding to a plurality of predetermined activities to be monitored, said processor circuit applying a control signal to said amplifier to maintain said amplified filtered detector output signal in said predetermined amplitude range.

9. An activity monitor as defined in claim 8 wherein said processor circuit includes a resident operating program for controlling the configuration of said filter circuits.

10. An activity monitor as defined in claim 9 wherein the monitor includes a data port, and said resident program is changeable through said data port.

11. An activity monitor as defined in claim 8 wherein said resident program is changeable in response to said sampled signals.

12. An activity monitor as defined in claim 7 including saturation inhibit means responsive to said filtered detector output signal for inhibiting the storing of said signal in the event said signal exceeds a predetermined threshold level.

13. An activity monitor as defined in claim 1 wherein the detector output signal includes a noise component, and said conversion means include a zero crossing detector having a predetermined threshold level greater than said noise component, and said designated body activity provides a detector output signal having an amplitude greater than the amplitude of said noise component and said predetermined threshold level.

14. An activity monitor as defined in claim 13 wherein said threshold level of said zero crossing detector is dependent on an applied control signal, and the monitor includes a processor circuit having a plurality of selectable operating modes corresponding to a plurality of predetermined activities to be monitored, each of said predetermined activities requiring a different zero crossing threshold, and the monitor further including a control circuit for applying a control signal to said zero crossing detector to configure the zero crossing threshold so that it corresponds to the selected operating mode.

15. An activity monitor as defined in claim 14 wherein said zero crossing detector comprises a window detector having upper and lower thresholds centered about a predetermined reference signal level, said thresholds being greater than said noise component relative to said thresholds.

16. An activity monitor as defined in claim 15, wherein said upper and lower thresholds of said window detector each vary from said reference signal level in response to said applied control signal.

17. An activity monitor as defined in claim 13 including saturation inhibit means responsive to said filtered detector output signal for inhibiting the storing of said signal in the event said signal exceeds a predetermined threshold level.

18. An activity monitor as defined in claim 1, wherein said processing circuit includes a timer for initiating changes in said operating mode at predetermined times.

19. An activity monitor as defined in claim 1, wherein said operating mode is changeable in response to said sample signals.

20. A programmable patient monitoring system for detecting and recording an occurrence or absence of at least one patient body movement in a human or animal patient over time, said patient monitoring system comprising:

an activity monitor securable to a desired location on a patient whose body movements are being monitored, said activity monitor including means for sensing movement of the patient's body and means for simultaneously generating an analog electrical signal having waveform configuration, frequency and amplitude characteristics reflective of the effect said at least one body movement has on said sensing means, said activity monitor further including a configurable amplifier means for selectively adjustably amplifying said analog electrical signal to a desired amplification level, configurable highpass filter means for attenuating a component portion of said analog signal having a frequency below a selectively adjustable lower threshold frequency; configurable lowpass filter means for attenuating a component portion of said analog signal having a frequency above a selectively adjustable upper threshold frequency; said activity monitor further including memory means of finite capacity, conversion means for sampling said selectively amplified and filtered analog signal, for converting said signal to a plurality of signal resultants and for storing the signal resultants in said memory means, said amplifier means, said highpass filter means and said lowpass filter means each being configurable in response to applied configuration control signals, said activity monitor further including a processor circuit having a plurality of programmably selectable operating modes corresponding to a plurality of configuration settings, each setting being specifically appropriate for monitoring a predetermined body movement, said processor circuit applying said configuration control signals to said lowpass filter, said highpass filter and said amplifier, whereby said patient monitoring system is programmed by said processor circuit to specifically detect and record movement data relating to said at least one predetermined human body movement.

21. A programmable patient monitoring system as defined in claim 20, wherein said processor circuit includes a resident operating program for controlling the configuration of said lowpass and said highpass filter means.

22. A programmable patient monitoring system as defined in claim 21 wherein the activity monitor includes a data port, and said resident program is changeable through said data port.

23. A programmable patient monitoring system as defined in claim 21, wherein said resident program is changeable in response to said sampled signals.

24. A programmable patient monitoring system as defined in claim 21, wherein said processing circuit includes a timer for initiating changes in said operating mode at predetermined times.

25. A programmable patient monitoring system as defined in claim 20 wherein each of said filter means includes an analog switch device responsive to said applied control signal for controlling said threshold frequency.

26. A programmable patient monitoring system as defined in claim 20 including saturation inhibit means responsive to said filtered analog electrical signal for inhibiting the storing of said signal in the event said signal exceeds a predetermined threshold level, said saturation inhibit means further including interactive software means responsive to said saturation inhibit means for altering configuration settings to prevent continued saturation.

27. A programmable patient monitoring system as defined in claim 20 further including detector means for developing a first resultant data signal indicative of a selected resultant mathematical parameter of said amplified, filtered analog signal and means for storing said first data signal in said finite memory.

28. A programmable patient monitoring system as defined in claim 27, wherein said detector means comprises a zero crossing detector having a threshold signal level, and said mathematical parameter is the time duration of said detector signal above said predetermined threshold.

29. A programmable patient monitoring system as defined in claim 27 wherein said detector means comprises a zero crossing detector having a threshold signal level, and said mathematical parameter is the frequency of said signal crossing said predetermined threshold.

30. A programmable patient monitoring system as defined in claim 27, wherein said detector means comprises a zero crossing detector having a threshold signal level, and said mathematical parameter including time-duration above threshold and frequency of threshold crossing are stored as resultant data signals in said memory.

31. A programmable patient monitoring system as defined in claim 30 including additional processing means for reconstructing the analog electrical signal from said stored resultant data signals.

32. A programmable patient monitoring system as defined in claim 20 further comprising computer means adapted to receive stored signal resultants from said memory means for further processing and adapted to transmit appropriate programming instructions to said processor circuit to alter or select a said operating mode and electrical interface means for electrically connecting said activity monitor to said computer.

33. A method for automatically monitoring predetermined body movements of a subject over time, said method comprising:

affixing a wrist-mounted activity monitor onto the non-dominant wrist of said subject thereby permitting the activity monitor to produce an analog electrical signal responsive to and characterized by said body movements, three-dimensionally tuning said activity monitor by selectively adjusting the upper and lower threshold frequencies to define a desired frequency band pass characteristic and adjusting the amplitude characteristics of said analog electrical signal to enhance relevant signal information and remove irrelevant signal information to provide an enhanced signal and thereafter, passing said enhanced signal through a converter means for selectively sampling said enhanced signal with respect to an appropriate real time epoch to provide resultant data signals, if any, which fall within known activity regions defined in a mutually orthogonal, three-dimensional coordinate axis system including a sensitivity axis, a frequency axis and an epoch axis, previously known to be specific for the predetermined body movement being monitored.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The subject invention relates to apparatus and methods for monitoring activity of the human body. More particularly, the invention relates to apparatus, systems and methods by which the occurrence and length of certain types of body movements which form activity phenomenon can be selectively observed and accurately quantified.

A human subject engages in a wide range of body movements. Such movements can range from the voluntary and visually perceptible--such as the movement of legs, arms and head, to the involuntary and visually imperceptible, such as the slight changes in elevation of skin caused by the rhythmic pulsations of blood and breathing.

The observation of body movement can provide much information useful to physicians and researchers. For example, by observing a subject's movements, the occurrence and length of natural phenomenon, such as wakefulness, rest and sleep can be determined. By observing the nature of a subject's movement, the occurrence and severity of disorders and the effects of drugs or other therapy can be assessed. In many cases quantification of the subject's movement is preferred so that the movement pattern of one subject can be compared with the movement pattern of others.

Direct visual observations of body movement are labor intensive, time consuming and tedious. Moreover, direct visual observations provide only a limited range of qualitative information, such as subjective descriptions of a subject's visually perceptible movements. Little, if any, quantification in readily comparable values, such as degree, strength, and/or violence of a subject's activity, and no information, either qualitative or quantitative, of a subject's visually imperceptible movements is obtained. Furthermore, the value of qualitative information obtained by directly observing a subject is subject to question as such observations themselves may cause the subject to become conscious of and thereby alter his or her movements.

Activity monitors have been developed for observing and quantifying certain aspects of movement without the involvement of an observer. However, such monitors had disadvantages which limited their usefulness. For example, such prior monitors were typically of a size which interfered with free movement of the subject, and typically had either little or no internal memory and/or little or no data processing capabilities. In order that data produced by many of these activity monitors could be stored and/or processed it was necessary to connect the monitors through cables to external data storage and processing devices. Tethering the monitor in this way to an external device also tethered the subject to the device, thereby restricting the subject's movement and biasing the results.

In those prior activity monitors which had internal memory, saturation of the memory occurred when the subject engaged in activity which produced a volume of data that, for the period of time over which the subject was being monitored, exceeded the capacity of the memory.

This problem was aggravated because prior activity monitors were not selectively configurable to collect data only for a particular activity, so that unusable or irrelevant data was often allowed to occupy memory space along with usable data. Prior monitors did not have the capability to be reconfigured according to preset instructions and/or in response to the data collected by the monitor.

Prior monitors typically utilized sensors to detect body movement which, because of the need to suppress harmonics and other artifacts from the limited memory, lacked the sensitivity to detect small scale, visually imperceptible movements such as those caused by breathing, the beat of the heart, and the flow of blood.

A demand therefore exists for an activity monitor and method by which the activity of a subject, even that activity which includes movements that are not necessarily visually perceptible, can be selectively observed and accurately quantified. The present invention satisfies this demand.

Accordingly, it is a general object of the present invention to provide an improved apparatus, system and methods for selectively observing and accurately quantifying certain aspects of the motion of a subject.

An object of the present invention is to provide an activity monitor having a size and construction such that the monitor may be conveniently worn on the subject.

Another object of the present invention is to provide an activity monitor which can collect data regarding a subject's activity automatically and according to instructions initialized in the monitor.

Another object of the present invention is to provide an activity monitor having a memory in which operating instructions and collected data are stored.

Another object of the present invention is to provide an activity monitor with which data regarding a subject's movement can be processed automatically and according to instructions initialized in the monitor.

Another object of the present invention is to provide an activity monitor wherein the type of data collected and the processing of the data by the monitor can be automatically changed.

SUMMARY OF THE INVENTION

The present invention is directed to an activity monitor and methods by which both visually perceptible and visually imperceptible movement can be selectively observed and accurately quantified.

The apparatus includes an activity monitor, or actigraph, having a size, shape and construction that allows the monitor to be worn on the surface of the skin of a subject and which functions reliably and without restriction of the subject's movement. One preferred embodiment of the monitor of the present invention is configured for wearing on a subject's non-dominant wrist. The monitor may be configured to be worn on other parts of a subject's body as well.

In particular, the activity monitor of the present invention includes a movement sensor by which the full range of a subject's movement, even that which is visually imperceptible, can be detected. A preferred sensor is a cantilever piezoelectric bimorph beam. The use of a bimorph beam as a sensor is advantageous in that it provides high sensitivity and operates without requiring any operating power, such as from a battery, thereby conserving this generally limited resource. Furthermore, such a sensor operates in the absence of a gravitational field thereby expanding the applications in which the monitor can be utilized.

The bimorph beam in response to an applied force produces a signal whose frequency varies according to the movement to which the monitor is subjected. When the monitor is secured adjacent to the surface of the skin of a subject, such as on the subject's non-dominant wrist, the monitor produces signals having frequencies ranging from approximately 0.16 hertz to 9 hertz. Within this frequency range, certain activities of the subject produce frequencies falling within certain specific narrow frequency ranges. For example, breathing produces a signal having a frequency range of 0.2 to 1 hertz, the beat of the heart produces a signal having a range of 2 to 3 hertz, and the typical night time activity of a subject produces a signal having a range between 0.2 and 3 hertz. Disorders, such as tremor activity, typically produce a signal having a range of 2 to 9 hertz.

So that such specific frequency ranges among the wide range of frequencies which a subject's many movements produce can be selectively observed and quantified, the activity monitor includes signal processing means which amplify, shape and filter the signal produced by the sensor.

In particular, so that a low amplitude signal, such as those produced by breathing and heart beats, can be isolated for later processing, the activity monitor includes signal conditioning means in the form of a motion signal amplifier having an amplification factor selectable by an applied configuration control signal, and a highpass filter circuit having a threshold selectable by another applied configuration signal below which motion sensor signals are greatly attenuated. This is advantageous in that it allows observations to be made of a subject both during a high activity period, when a relatively high amplitude high frequency signal is produced by the sensor, and during a low activity period, such as during the night, when the subject is typically producing a relatively low amplitude and low frequency signal.

To eliminate DC drift in the motion signal amplifier the signal processing means preferably include a drift compensation circuit which compares the dc level of the amplified motion signal developed by the amplifier with a fixed dc reference voltage to develop a drift corrected voltage at the motion detector which nulls out any drift.

To eliminate artifacts present in the sensor output signal, such as those caused by the natural resonance of the motion sensor, and to obtain in conjunction with the highpass filter a desired frequency spectrum for analysis and quantification, the activity monitor includes a low pass filter circuit having a threshold frequency selectable by applied configuration signals.

The activity monitor further includes an analog-to-digital converter which samples the analog signal developed by the motion sensor, after processing by the amplifier, high-pass filter and low-pass filter, and passes the resultant digital values to internal memory means in the monitor for storage and later retrieval.

The activity monitor also includes a window detector which compares the voltage level of the processed motion signal to upper and lower voltage thresholds selectable by an applied configuration signal, and provides an activity count each time the signal voltage level crosses the thresholds. Preferably, the signal voltage level is compared to both a high threshold voltage level and a low threshold voltage level which are symmetrically positioned opposite the regulated reference voltage. Preferably, the amount by which the upper and lower thresholds differ exceeds the amount of noise which the system normally generates so that counts generated by the detector are caused by variations in the motion detector output signal and not by monitor noise.

The activity monitor further includes a temporary internal memory for recording the activity counts generated by the activity detector over a selectable observation period, or epoch. At the end of the epoch, the total number of events occurring during the epoch is stored, and the temporary memory is erased for use during the next epoch. Advantageously, the epoch time period is selected according to the type of activity to which the observation is directed. For example, because a subject engages in generally less movement while asleep, the epoch used during such an observation period can be generally of greater duration than that, for example, used when a subject is monitored while awake. A selectable epoch period avoids the memory saturation problem that prior monitors had in collecting data for periods of time inappropriate to a particular type of movement.

The activity monitor also includes an internal micro-processor having resident software by which the configuration of the various circuits of the monitor are controlled. The microprocessor is preferably capable of powering up and shutting down the processing circuits at selected times to conserve battery power.

The microprocessor has associated with it memory in which software to control the monitor components is resident and in which data obtained from the operation of the monitor is stored. Specifically, the memory includes a read-only memory (ROM) which contains instructions to operate the monitor. Preferably, the ROM includes an operating system by which the monitor's signal processing components can be initially configured so that, for example, certain aspects of a subject's movement can be initially observed, from which the monitor's signal processing components can be reconfigured so that other aspects of a subject's movement can be observed, and by which the data that is collected is stored.

Advantageously, to provide an activity monitor which is fully adaptable and which can be altered to collect data regarding activity patterns not initially envisioned, the monitor memory includes a random-access memory (RAM) for storing instructions, for example, different from those stored in the ROM. Advantageously, the monitor can operate off either, or a combination of those instructions stored in the ROM or in the RAM.

Communication between the activity monitor and, for example, a personal computer, with which the data obtained by the monitor be stored, evaluated, and further processed, and from which new instructions to be stored in the monitor RAM can be prepared, is facilitated by an interface unit providing electrical connections between the monitor and the computer. To this end, the interface unit preferably includes a receptacle for receiving the monitor, and the monitor is provided with an electrical connector on the surface of its housing which engages a complementary connector in the receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is a perspective view of a wrist-mounted activity monitor constructed in accordance with the invention as worn on the wrist of a subject.

FIG. 2 is an activity monitoring system including a computer, interface and wrist-mounted activity monitor constructed in accordance with the invention.

FIG. 3 is an enlarged perspective view of a portion of the interface unit shown in FIG. 2 showing the positioning of the wrist-mounted activity monitor therein.

FIG. 4 is a functional block diagram showing the principal components of the activity monitoring system of FIG. 2.

FIG. 5 is an enlarged plan view of the control panel of the wrist-mounted activity monitor of FIGS. 1-3.

FIG. 6 is an exploded perspective view of the wrist-mounted activity monitor showing certain principal components thereof.

FIG. 7 is an enlarged perspective view of the piezoelectric bimorph beam motion detector utilized in the activity monitor of FIGS. 1-3.

FIG. 8 is a functional block diagram showing the principal components and circuits of the activity monitor of FIGS. 1-3.

FIG. 9 is a simplified schematic diagram of the activity monitor described in FIG. 8.

FIG. 10 is an illustrative plot of the frequency spectrum of five different activities of the human body.

FIG. 11 is a simplified depiction of the frequency spectrum and signal characteristics of five specific activities of the human body.

FIG. 12 is a simplified schematic diagram and plot illustrating the characteristics of the piezoelectric bimorph beam sensor utilized in the activity monitor of the invention.

FIG. 13 is a graphical depiction of certain voltage relationships associated with the window detector utilized in the activity monitor of the invention.

FIG. 14 is a graphical depiction of certain bandpass characteristics associated with the high-pass filter utilized in the activity monitor shown in FIGS. 8 and 9.

FIG. 15 is a depiction of a sinusoidal waveform illustrating certain parameters thereof.

FIG. 16 is a depiction of a repetitive waveform showing certain zero-crossing parameters thereof.

FIG. 17 is a three-dimensional depiction of certain axes useful in analyzing activity of the human body.

FIG. 18 is a 3-dimensional depiction of certain activities of the human body viewed along the axes of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the Figures, and particularly to FIGS. 1 and 2, a wrist-mounted activity monitor or actigraph 10 constructed in accordance with the invention may be similarly shaped and sized to a wrist-watch, having a flexible band 11 securing a generally rectangular housing 12 against the skin surface of a subject being monitored. Typically, in this form the monitor is mounted on the non-dominant wrist, the activity of which has been found to correlate with body activity, muscle movement and brain waves.

In use, the activity monitor 10 is worn by the subject for a predetermined collection period which may extend over one or more days. Data collected by the monitor over the collection period is downloaded at the end of the period to a personal computer 13 which, except for containing necessary software for accomplishing the down-loading of data from the monitor and the uploading of operating instructions to the monitor, may be entirely conventional in construction and operation. Communication between the activity monitor 10 and computer 13 is facilitated by an interface unit 14, which is connected to a data port of computer 13 by means of a conventional RS-232 cable 15 or the like. The interface unit 14 preferably includes a receptacle 16 (FIG. 3) on its top surface dimensioned to receive the monitor housing 12. An electrical connector 17 located along one side of receptacle 16 engages a connector 18 on housing 12 when the monitor is seated within the receptacle. With this arrangement the monitor can be quickly and conveniently installed and removed from interface unit 14. A plurality of controls 20 on the top surface of interface unit 14 assist the operator in accomplishing the downloading and uploading functions.

Activity monitor 10, personal computer 13 and interface unit 14 together comprise a system for collecting and analyzing human activity data. Depending on the particular software resident in personal computer 13 a wide variety of written reports and displays may be generated from the data collected by the monitor.

In this regard, and with reference to FIG. 4, data is exchanged between personal computer 13 and interface unit 14 in both directions, and between interface unit 14 and activity monitor 10 in both directions. This provides complete flexibility in that necessary operating instructions may be provided to monitor 10 through interface unit 14 from personal computer 13. When the monitor is removed from interface unit 14, these resident instructions control the operation of the monitor in a subsequent data collection assignm