Abstract:
Apparatus and methods for performing remote detection of physiological activity are described. One aspect of the invention involves obtaining information concerning respiration and heart function. In one embodiment, the invention includes a source containing an oscillator configured to illuminate the subject with electromagnetic signal beam and a receiver configured to observe changes in the amplitude of the electromagnetic signal reflected by the subject.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority based on U.S. Provisional Application No. 60/400,399, filed Aug. 1, 2002, and U.S. Provisional Application No. 60/473,670 filed May 23, 2003, the disclosure of which is incorporated herein by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   The U.S. Government has certain rights in this invention pursuant to NAS7-1407 provided by the National Aeronautics and Space Administration, Office of Space Science. 

   BACKGROUND OF THE INVENTION 
   Information concerning a patient&#39;s breathing and heart function can be vital to the diagnosis and monitoring of many medical conditions. A electrocardiograph is a device that is commonly used to provide information concerning heart function. Electrocardiographs provide outputs that are indicative of electric fields created by the heart as it beats. Operation of an electrocardiograph typically requires attachment of nine leads, which are combined to obtain twelve sets of measurements. A large body of clinical experience has been amassed which has revealed correlations between specific shapes in the output of an electrocardiograph and many different types of heart conditions. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention are capable of detecting physiological activity. In one aspect of the invention, motion can be detected. In another aspect, specific physiological activity such as respiration, heart rate or the electrophysiology of a heart can be monitored. In one embodiment adapted for monitoring the physiological activity of a subject, the invention includes a source containing an oscillator configured to illuminate the subject with an electromagnetic signal beam and a receiver configured to observe changes in the amplitude of the electromagnetic signal reflected by the subject. 
   In a further embodiment, the invention includes an RF oscillator connected to a first antenna portion, where the RF oscillator and the first antenna portion are configured to generate a electromagnetic signal beam that illuminates the subject and a detector connected to a second antenna portion, where the second antenna portion and detector are configured to generate a signal indicative of the amplitude of the electromagnetic signal reflected by the subject. 
   One embodiment of the method of the invention includes illuminating an area with an electromagnetic signal having a wavelength that renders at least some debris transparent and detecting the amplitude of reflections of the electromagnetic signal and observing variations in the amplitude. 
   A further embodiment of the invention includes illuminating the subject with an electromagnetic signal beam and observing changes in the amplitude of the electromagnetic signal reflected by the subject. 
   Another embodiment of the method of the invention for generating an electrocardiogram includes illuminating a heart with an electromagnetic signal beam and detecting the amplitude of the electromagnetic signal reflected by the heart. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a remote-detection system in accordance with an embodiment of the present invention illuminating a subject with an electromagnetic signal; 
       FIG. 2  is a block diagram of the components of a system in accordance with an embodiment of the present invention; 
       FIG. 3A  is a schematic illustration of three orthogonal components of the dipole of a heart during depolarization and repolarization; 
       FIG. 3B  is a graph showing the amplitude of reflected electromagnetic signal measured in accordance with an embodiment of the present invention; 
       FIG. 3C  is a graph showing a signal that results when the signal illustrated in  FIG. 3C  is low pass filtered and normalized; 
       FIG. 4A  is a graph illustrating the amplitude of the reflected electromagnetic signal measured in accordance with an embodiment of the present invention from a distance of two feet; 
       FIG. 4B  is a graph illustrating the amplitude of the reflected electromagnetic signal measured in accordance with an embodiment of the present invention from a distance of eight feet; 
       FIG. 5  is a schematic diagram illustrating an embodiment of a detector in accordance with the present invention including separate antennas for generating and detecting an electromagnetic signal; and 
       FIG. 6  is a block diagram showing an embodiment of a remote-detection system in accordance with the present invention that includes separate antennas for generating and detecting an electromagnetic signal. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention use reflected electromagnetic signals to observe breathing, pulse and/or to generate an electrocardiogram of a subject. Other embodiments of the invention can be used to make observations concerning the function of neurons or other tissue types that are capable of generating an electric field. Remote-detection systems in accordance with the present invention typically work by using an RF oscillator to generate an electromagnetic signal beam that is then used to illuminate a subject. In operation, the subject&#39;s breathing, motion of the subject&#39;s heart beating and the depolarization and repolarization of the heart cells that accompany each heart beat can all contribute to variations in the amplitude of the electromagnetic signal reflected by the subject. An output indicative of the amplitude of the signal reflected by the subject is generated and signal processing techniques can be performed to extract the portions of the output that are indicative of the respiration rate, the pulse rate and/or the electrocardiogram of the subject. 
   Turning now to the diagrams,  FIG. 1  illustrates a remote-detection system  10  in accordance with the present invention that includes an antenna  12  coupled via a directional coupler  14  to an RF oscillator  16  and a RF detector  18 . In addition, the RF detector is connected to a digital signal processor  20 . The RF Oscillator and the antenna can illuminate a subject  24  with an electromagnetic beam  22 . The subject typically reflects a portion of the incident electromagnetic signal and the antenna and the RF detector can be used to generate a signal indicative of the amplitude of the reflected signal. Information can then be extracted from the signal generated by the antenna and the RF detector by the digital signal processor  20 . 
   When a subject is illuminated with an electromagnetic signal generated by a remote-detection system  10  in accordance with the present invention, the electromagnetic signal can be reflected as a result of the signal encountering a boundary between materials having different complex impedances. The complex impedance of a material is the property that determines the change in amplitude and phase shift of an electromagnetic wave reflected at an interface between that material and another material. The complex impedance of a material may change with the introduction or removal of free charge on the surface of the material. In the illustrated embodiment, the subject is a human and the electromagnetic signal beam  22  illuminates the subject&#39;s chest  26 . Air has a comparatively low complex impedance compared to the complex impedance of human tissue. Therefore, a significant amount of any electromagnetic signal illuminating a human subject will be reflected by the subject&#39;s body. The pattern of the reflected signal will depend on the shape of the subject&#39;s body. Changes in the shape or position of a subject&#39;s chest associated with respiration can alter the pattern of the reflected signal in ways that can be observed using the antenna. 
   A beam  24  with appropriate intensity can illuminate a subject&#39;s heart  28 . The amount of the electromagnetic signal reflected by the heart depends upon the complex impedance of the heart cells, which changes as the heart beats. When the heart beats, the heart cells are initially polarized due to an imbalance in the concentration of ions on either side of the cell membrane. As the heart muscles contract, the cell membranes of the heart muscle cells become permeable and the concentration of ions on either side of the membrane balances. All of the heart muscle cells do not depolarize simultaneously. Rather, a depolarization wave sweeps across the heart starting in the atria and moving to the ventricles. Once the heart has finished contracting, the heart muscle cells repolarize. The imbalance of ions on either side of a the cell membranes of polarized heart cells gives them a complex impedance that is significantly different to that of the tissue surrounding the heart. Therefore, electromagnetic signals will be reflected by polarized heart cells. The depolarization of heart muscle cells changes the complex impedance of the heart muscle cells. Consequently, the motion of the heart and the depolarization and repolarization of the heart muscle cells will both have an effect on the pattern of electromagnetic signals reflected by the heart. Observing the changes in reflections from the heart over time in accordance with the present invention can provide information about the frequency with which the heart beats and the electrophysiology of the heart. 
   A block diagram of a remote-detection system in accordance with the present invention is illustrated in  FIG. 2 . The remote-detection system  10 ′ includes a synthesized RF oscillator  40  that is connected to a common node  42  and a first amplifier  44 . The common node  42  is connected to an oscillator  46  and a lock-in amplifier  48 . The output of the first amplifier  44  is connected to an antenna  50  via a directional coupler  52 . The directional coupler is also connected to a second amplifier  54 . The output of the amplifier is connected to a mixer  56 . An RF oscillator  58  also provides an output to the mixer. The output of the mixer is connected to the input of a third amplifier  60 . The output of the third amplifier is connected to a bandpass filter  62  and the output of the bandpass filter is connected to a diode detector. An output of the diode detector is connected to an input of the lock-in amplifier  48  and the output of the lock-in amplifier is then provided to a data acquisition computer  66 . 
   In one embodiment, the synthesized RF oscillator  40  produces an electromagnetic signal in the range of 20 GHz and can be implemented using a Model 33120A manufactured by Hewlett-Packard Company of Palo Alto, Calif. The first amplifier  44  boosts the strength of the signal and is implemented using a 2-20 GHz amplifier such as a Model 8349B manufactured by the Hewlett-Packard Company. The oscillator  46  generates a kilohertz range modulation signal and is implemented using a Model 83723B manufactured by Hewlett-Packard Company. The lock-in amplifier  48  synchonously detects the kilohertz amplitude-modulated output from the diode detector  64  and can be implemented using a Model SR830 manufactured by Stanford Research Systems of Sunnyvale, Calif. The waveguide horn antenna  50  produces the radiated signal beam and is implemented using a Model 639 manufactured by the Narda division of L-3 Communications Corporation of New York, N.Y. The directional coupler  52  couples the signal to be radiated to the antenna  50  and is implemented using a Model P752C-10 dB manufactured by the Hewlett-Packard Company. The second amplifier  54  provides a low-noise amplification of the reflected signal and is implemented using a 20 GHz amplifier such as a Model AMF-3D-000118000-33-10P manufactured by MITEQ, Inc. of Hauppauge, N.Y. The 2nd harmonic mixer  56  down-converts the signal to 1 GHz and can be implemented using a Model SBE0440LW1 manufactured by MITEQ, Inc. The RF oscillator  58  serves as the local oscillator for the mixer  56  and is implemented using a Model 8340A manufactured by Hewlett-Packard. The third amplifier  60  boosts the signal to a level aappropriate for the diode detector  64  and can be implemented using a 1 GHz amplifier such as a Model 4D-00011800-33-10P manufactured by MITEQ, Inc. The bandpass filter  62  limits the signal reception bandwidth in order to reduce the noise of the detection system and can be implemented using a 300 MHz bandpass filter such as a Model 381-1390-50S11 manufactured by Reactel, Incorporated of Gaithersburg, Md. The diode detector  64  produces a video response proportional to the amplitude of the reflected electromagnetic signal and can be implemented using a Model 8473C manufactured by the Hewlett-Packard Company. The data acquisition computer  66  digitizes the output of the lock-in amplifier  48 , stores the signal, and displays it in a graphical format and can be implemented using a Macintosh Model 8600/300 manufactured by Apple Computer, Inc. of Cupertino, Calif. 
   As discussed above, the depolarization and repolarization of the heart generates an electric field and changes the complex impedance of the heart. The electric field generated by the heart can be modeled as a dipole moment. The dipole moment of the heart is created as a result of a portion of the heart being polarized and a portion of the heart being depolarized. Therefore, the changes in strength and direction of the dipole moment of the heart provide information concerning the electrophysiology of the heart. The dipole of the heart during the depolarization of the atria generates a P-wave on an electrocardiograph. The dipole of the heart during the depolarization of the ventricles generates a series of waves on the output of an electrocardiograph known as the “QRS complex”. The change in dipole associated with the repolarization of the ventricles generates an output on an electrocardiograph known as a T-wave. These waves and complexes are commonly used in medical diagnosis. A further description of the electric field and physiology of the heart as it beats is described in the paper published by R. K. Hobbie in the American Journal of Physics, vol. 41, p.824 (1973) entitled “The Electrocardiogram as an Example of Electrostatics”, which is incorporated herein by reference in its entirety. 
   Orthogonal components of the dipole moment of the electric field generated by a heart during two successive beats are illustrated in  FIG. 3A . The magnitude of the orthogonal components of the electric field during the P wave ( 80 ), the QRS complex ( 82 ) and the T wave ( 84 ) are indicated on the graph representing the x, y, and z-components of the electric field. 
   A graph illustrating an output from a remote-detection system,  10  in accordance with the present invention taken when the system was used to illuminate and observe the reflections from a human subject&#39;s chest is illustrated in  FIG. 3B . The graph  100  contains a series of large features  102  that are spaced approximately 6 seconds apart and are indicative of the respiration of the subject. In addition, the graph  100  contains a number of smaller features  104  that are spaced less than two seconds apart and are indicative of the beating of the subject&#39;s heart. 
   A graph of a second output of a remote-detection system,  10  in accordance with the present invention is illustrated in  FIG. 3C . The second output has been low-pass filtered to smooth away low frequency signals. An effect of the low-pass filtering is to remove the component  102  of the output illustrated in  FIG. 3C  that is indicative of the respiration of the subject. The graph  120  shows a series of peaks that correspond to a P-wave  122 , a QRS complex  124  and a T-wave  126 . The output graphed in  FIG. 3C  provides information about a portion of the electrophysiology of the heart as it beats. In order to form a complete picture of the heart (i.e. containing at least as much information as a conventional 12-lead electrocardiogram), three orthogonal measurements can be taken using a single or multiple remote-detection systems in accordance with the present invention. Linear algebra can be used to construct the “12-lead” responses from the three orthogonal components measured with the remote-detection system in accordance with the present invention, to build a complete impression of the electrophysiology of the heart as it beats. 
   As discussed above, a remote-detection system in accordance with the present invention is capable of obtaining a considerable amount of information concerning a subject. The particular information obtained by the remote-detection system is dependant upon the application. In one embodiment, the detector monitors a subject&#39;s respiration and pulse rates. In other embodiments, the detector can obtain an electrocardiogram or monitor muscular or neural function. Alternatively, a detector in accordance with the present invention may simply detect the presence of a living creature either as a security device or to assist rescuers in locating trapped or unconscious people. 
   In many embodiments involving a human subject, the signal generated by the remote-detection system is in a frequency range of 10 GHz to 80 GHz with a beam width of three feet at a distance of 26 feet. Typically, a three foot wide beam is sufficient to localize a single person without interference. In other embodiments, signals in the range of 1 GHz to 100 GHz can be used. Alternatively, embodiments could use signals in the range of 100 MHz to 200 GHz. 
   The width of the beam required depends on the application. For example, a broad beam could be used where a detector is attempting to detect the presence of a life form in a collapsed building. A narrow beam could then be used to determine the specific location of the detected life form. In medical diagnostic applications, an appropriate beam would have sufficient width to obtain reflections from the required portions of the subject&#39;s body and be sufficiently narrow to avoid unwanted reflections. Where Microwave Monolithic Integrated Circuit (“MMIC”) technology is used to construct remote-detection systems in accordance with the present invention, two patch antennas separated by four inches could produce the three foot wide beam described above. The effective range of the system would effectively scale with antenna size and transmitted power. Where antenna size is an issue, increasing the frequency of the electromagnetic radiation would enable the construction of smaller antennas. However, the amplitude of the reflected signals will typically decrease as the frequency of the signal increases. 
   The ability of a remote-detection system in accordance with the present invention to operate through structures or debris is dependent upon the materials composing the structures or debris. Many materials such as bricks, wood or cinderblocks are transparent to electromagnetic signals of frequencies in the ranges described above. However, water in concrete and the presence of metal can interfere with the signals received by the remote-detection system. 
   In other embodiments, remote-detection systems in accordance with the present invention can be used to monitor neural or muscular function. In addition, a remote-detection system could also be used as a monitor for sudden infant death syndrome or for sleep apnea. The applications of the remote-detection system also include exercise equipment, where the remote-detection system can be used to monitor pulse and/or respiration during an aerobic workout. In all instances the remote-detection system is placed a distance from the subject and measurements are made without the need for contact between the system and the subject. The applications of the remote-detection system are not limited to human subjects or human tissue. The devices and principles described above can be equally applied to detection and monitoring of other life forms. 
   As discussed above, remote-detection systems in accordance with the present invention can work effectively at considerable distances from the subject. A graph illustrating an output from a remote-detection system in accordance with the present invention that was used to monitor the heart rate of a subject located approximately 2 feet from the system is illustrated in  FIG. 4A . The graph  160  contains periodic peaks  162  that are spaced less than 1 second apart. These features are indicative of the subject&#39;s heart beating. 
   A graph illustrating an output from a remote-detection system in accordance with the present invention that was used to monitor the heart rate of a human subject located approximately 8 feet from the remote-detection system is illustrated in  FIG. 4B . Again, the graph  180  includes a series of periodic peaks  182  spaced less than a second apart. The graph trends downward over a period of eight seconds due to a drift in the DC level of the measurement. 
   An embodiment of a remote-detection system in accordance with the present invention that includes separate antennas for illuminating a subject and for receiving reflections is illustrated in  FIG. 5 . The remote-detection system  10 ″ is similar to the embodiment illustrated in  FIG. 1 , except that a first antenna  180  is used to generate an electromagnetic signal beam and a second antenna  182  is used to detect the reflected electromagnetic signal beam. 
   A block diagram of a remote-detection system  10 ″ including two antennas is shown in  FIG. 6 . The remote-detection system  10 ″ includes a function generator  184  that is connected to a common node  185 . A synthesized RF oscillator  186  is also connected to the common node  185  and to a first amplifier  188 . The output of the first amplifier is provided to a waveguide horn antenna  180  via a coax-to waveguide transition  189 . A second antenna  182  is contained in a cryostat  190  and includes a silicon bolometer  192  and a Winston cone  193 . The electromagnetic signal is admitted through a window  194  in the cryostat and outputs from the silicon bolometer are provided to a lock-in amplifier  196  via a second amplifier  198 . The lock-in amplifier is connected to the function generator  184  via the common node  185  and to a data acquisition computer  200 . 
   The function generator  184  produces a kilohertz range modulation signal and can be implemented using a Model 33120A manufactured by the Hewlett-Packard Company. The synthesized RF oscillator  186  produces an electromagnetic signal in the range of 20 GHz and can be implemented using a Model 83723B manufactured by the Hewlett-Packard Company. The first amplifier  188  can be implemented using a 10 dB RF amplifier such as a Model 8349B manufactured by the Hewlett-Packard Company. The waveguide horn antenna  180  produces the radiated signal beam and can be implemented using a Model 33120A manufactured by Microlab/FXR of Livingston, N.J. The cryostat with silicon bolometer  182  detects the amplitude of the reflected electromagnetic signal and can be implemented using a Model HDL-5 manufactured by Infrared Laboratories, Inc. of Tucson, Ariz. The lock-in amplifier  196  synchronously detects the kilohertz amplitude-modulated output from the silicon bolometer  192  and can be implemented using a Model SR830 manufactured by Stanford Research Systems. The second amplifier  198  boosts the output of the silicon bolometer  192  and can be implemented using a 20-30 dB amplifier such as a Model LN-6C manufactured by Infrared Laboratories, Inc. The data acquisition computer  200  is implemented using a Macintosh 8600/300, manufactured by Apple Computer, Inc. 
   While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as an example of one embodiment thereof. Many other variations are possible, including implementing remote-detection systems in accordance with the present invention using planar antennas and MMIC manufacturing techniques. In addition, any process, physiological or otherwise, can be monitored that involves variations in patterns and/or intensity of reflected electromagnetic radiation using remote-detection systems in accordance with the present invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.