Abstract:
A small portable instrument monitors residual muscle tension as indicated by electrical activity from electrodes monitoring the muscles. A bio feedback signal is generated whenever tension exceeds a preset threshold and slows or stops as the tension is reduced towards the threshold. The bio feedback signal enables the user to learn how to voluntarily reduce excess muscle tension and lessen harmful health effects caused by stress. The instrument is battery powered, miniaturized and is designed to fit into an ambulatory setting.

Description:
FIELD OF THE INVENTION 
     The invention relates to a portable apparatus and a method for detecting and reducing tension and stress in a human subject using bio feedback. 
     BACKGROUND 
     Stress is an everyday fact of life for millions of people. Stressful situations are often found in the workplace and at home. This stress can lead to long-term physical and psychological problems. Research has shown that stress can be reduced through the alteration of brain wave patterns that the brain uses in order to function. Stimuli, such as sound and light, can affect and actually alter the flow of these brain wave patterns. 
     Bio feedback systems are known in the art for use in detecting levels of stress in subjects and providing the appropriate stimuli to affect and alter the flow of brain wave patterns. Bio feedback systems monitor and process bioelectrical signals generated in specific topological regions of a human subject&#39;s nervous system and produce a sensory stimulus when the system detects the presence or absence of certain characteristics in the signal. These characteristics may be correlated with a desired condition of the human subject&#39;s nervous system. The sensory stimulus provided by the bio feedback system, typically an audio or visual stimulus, or a combination of the two, is fed back to the human subject who associates the presence of the stimulus with the goal of achieving the desired condition of the nervous system. By responding to the stimulus, the human subject can be trained to control the wave form patterns of the monitored bioelectrical signals and thereby control the nervous system. Such a bio feedback system is disclosed in U.S. Pat. No. 3,727,616 to Ross. 
     Because bio feedback devices operate on the basis of internal stimuli, that is stimuli produced in response to bioelectrical signals generated by the human subject, the success of the bio feedback device depends upon a human subject attempting to consciously control a state of stress. Many people cannot affect such control over their involuntary nervous systems. In addition, bio feedback systems are usually expensive, require complex equipment, and require an expert to operate. 
     Prior art devices have attempted to overcome these limitations by producing a state of mental harmonization or relaxation in a human subject without detecting the state of stress, that is, through the use of a program of external stimuli. However, such systems do not provide a stress detection system and, therefore, the stimuli cannot be tailored to a human subject&#39;s changing state of stress and individual needs. 
     SUMMARY OF THE INVENTION 
     Tension and stress in human subjects may result in involuntary muscle movement. This muscle activity in the human body is initiated by electrical nerve impulses from the brain. These impulses may be measured at the surface of the skin as a voltage. The magnitude of the voltage signal is very small, on the order of micro volts. The magnitude of the electrical activity varies proportionately with the force of the muscle movement. 
     A small portable instrument is used to monitor residual muscle tension, as indicated by electrical activity from spurious motor neuron firings. The instrument is connected to one or more electrodes that receive electrical impulses created by activated nerves in the human subject&#39;s muscle groups. A bio feedback signal is generated whenever tension exceeds a pre-set threshold and slows or stops as tension is reduced towards the threshold. This enables the user to learn how to voluntarily reduce excess muscle tension and lesson the harmful health effects caused by stress. The instrument is battery powered and is miniaturized to fit comfortably on a human subject, such as in a shirt pocket. Alternatively, the instrument may be attached to the clothing of the human subject by velcro or by a clip-on device, or may be attached to the body of the human subject using a band with a velcro fastener, for example. 
     In an embodiment, three electrodes are attached to the skin of the human subject, along a chosen muscle group. A sensitive instrument amplifier detects differential voltage, while rejecting common mode signals. The desired signals are isolated through a band pass filter, of approximately 100 Hz, for example. The signals are then amplified. Signals that exceed a set point are integrated and produce a feedback signal through a small speaker, at a rate proportional to the amount of muscle tension. 
     The electrodes may be attached to the human subject on a desired muscle group, such as the trapezius muscles (shoulder and back), for example. 
     The instrument is ideal for a person sitting at a desk, using a computer keyboard, or any other position or situation where a person has a tendency to build up tension and stress in the neck, shoulders and back muscles. Such stress, if not reduced, may cause disturbing irritability, headaches, shoulder pain, back pain, carpal tunnel syndrome, tingling and numbness in fingers, hands and arms, or any other pain associated with stress buildup. 
     The apparatus and method may be used by the human subject to learn when tension and stress will occur. By repeatedly using the apparatus, the human subject will learn what activities or conditions are likely to cause high levels of tension and stress. The human subject can then modify or avoid the activities or conditions so as to prevent the buildup of harmful stress. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the following drawings, in which like numerals refer to like items and wherein: 
     FIG. 1 a  is a top perspective view of a portable apparatus for detecting and measuring tension and stress in a human subject and displaying an indication thereof; 
     FIG. 1 b  is a bottom perspective view of the apparatus of FIG. 1 a;    
     FIGS. 2 a - 2   d  illustrate example measurement points on the human subject; 
     FIG. 3 is a block diagram of the apparatus of FIG. 1 a;    
     FIG. 4 is a schematic diagram of a control and display circuit of the apparatus of FIG. 1 a ; and 
     FIG. 5 is a schematic diagram of a power supply of the apparatus of FIG. 1 a.    
    
    
     DETAILED DESCRIPTION 
     The invention is a portable apparatus and a method for detecting tension and stress in a human subject and for displaying an indication of such stress. The apparatus and method offer considerable advantage over prior art systems. In particular, the apparatus does not require a skilled operator to install or monitor and provides an output that is readily understood by the human subject, even when the human subject has no training in interpreting bio feedback responses. Moreover, the apparatus is adjustable so that the apparatus can be used by different individuals without a time consuming and costly calibration. The apparatus is portable, making it ideal for ambulatory subjects. Thus, the apparatus is readily usable in a variety of work environments. Costly overhead, clinics and other complications associated with traditional bio feedback systems are eliminated by the invention. The invention allows a human subject to readily and easily self-monitor for the onset of excessive tension and stress. The invention also allows the human subject to learn which situations are likely to cause tension and stress, and to therefore avoid such situations. 
     Stress may be detected by a number of different mechanisms. For example, higher breathing rates and heart rates are often associated with high levels of stress. Similarly, galvanometric skin resistence and brain wave activity can also be used to measure stress. In addition, stress in human subjects may cause muscles, such as the muscles of the neck, upper back and shoulders to contract. This contraction generates small but measurable voltages on the skin surface. These voltages, in the microvolt range, can be detected by using sensitive electrode sensors attached to the skin along the muscle of interest. 
     FIG. 1 a  shows a top perspective view of a portable apparatus  100  for detecting and indicating stress in a human subject. The apparatus  100  includes a casing  104  enclosing the electronics of the apparatus  100 . The casing  104  is small and lightweight, and may be sized to fit into any shirt pocket or may clip on, for example. The casing  104  may have a length of four inches, a width of 2.5 inches and a thickness of one inch, for example, and can be made even smaller. The casing  104  may be formed from any suitable plastic material or from a lightweight metal, or a combination of the two. The electronics of the apparatus  100  will be described in detail later. The apparatus  100  includes an on/off switch  101  by which electrical power is connected to the electronics. Signals from the human subject are provided to the apparatus  100  through wiring harness  102 . Wires in the wiring harness  102  terminate in attachments  106  that may be used to connect to electrodes (not shown). The electrodes are mounted directly on the human subject&#39;s chosen muscle group by way of adhesion, for example. The attachments  106  may be snap connections that are easily attached to and removed from the electrodes. 
     Also shown in FIG. 1 a  is a volume control switch  111  that is used to control an output volume of the apparatus  100  and a threshold switch  103  that is used to set a threshold value to indicate an onset of stress. The switch  103  may be a slider switch, for example. Using the switch  103 , the human subject can select an onset level, which, when exceeded, will lead the apparatus  100  to produce an audible output signal. The volume control switch  111  can be used to vary the intensity of the output audible signal. In use, the apparatus  100  can be placed in a shirt pocket, may be attached using a velcro fastener, or may clip on, for example. The wiring harness  102  can then be led to electrode attachment points on the human subject&#39;s muscle group. 
     FIG. 1 b  shows a bottom perspective view of the apparatus  100 . As shown in FIG. 1 b , the apparatus  100  includes a speaker face  105  through which the audible signal generated by the apparatus  100  is provided for display to the human subject. 
     While FIG. 1 a  shows the apparatus  100  including a wiring harness  102 , the apparatus  100  could also incorporate a radio frequency receiver that receives a radio frequency signal from wireless electrodes attached to the human subject. In this alternative, the wiring harness  102  is not required. Such an arrangement would increase the portability of the apparatus  100  and may make the apparatus  100  even more acceptable in a work environment. FIG. 2 a  shows possible contact points  107  for attaching the electrodes associated with the apparatus  100  to the human subject. As shown in FIG. 2 a , the three contact points  107  are displayed along the shoulder or the upper back muscles (e.g., the trapezius or the latisimus dorsi) of the human subject. As shown in FIG. 2 a , and as will be discussed below with respect to the electronics of the apparatus  100 , three electrode contact points may be selected. However, the apparatus  100  is not limited to the use of three contact points. Any number of electrode contact points may be implemented in the apparatus  100 . 
     FIGS. 2 b  - 2   d  show alternate contact points for the electrodes. FIG. 2 b  shows contact points  107 ′ on the forehead. FIG. 2 c  shows contact points  107 ″ on the forearm flexor. FIG. 2 d  shows contact points  107 ′″ on the forearm extender. 
     Although FIGS. 2 a - 2   d  show three separate contact points, indicating separate attachment of three electrodes to the human subject, one or more electrodes may be incorporated into a strap or band that is then attached to the human subject. The band  109  is designed to place the electrodes  108  over a surface of the chosen muscle group. For example, the electrodes  108  could be incorporated into a band that fits around the human subject&#39;s chest. When worn, the band may then place the electrodes  108  over the latisimus dorsi muscles, for example. The electrodes  108  may be of a conventional design and may be coupled to the apparatus  100  using the wiring harness  102 . Alternatively, the electrodes  108  may incorporate radio frequency technology such that signals detected by the electrodes  108  are passed to the apparatus  100  using radio frequency signaling. 
     FIG. 3 is a block diagram of the electronic components of the apparatus  100 . Signal line  112  provides a signal input from the wiring harness  102  (shown in FIG. 1 a ) to a receiver/instrument amplifier  110 . The receiver/instrument amplifier  110  may be a differential amplifier that rejects common mode signals on the electrodes and passes differential signals, on the order of microvolts, that are generated as a result of neuron firings in the chosen muscle group. In an alternative embodiment, the receiver/instrument amplifier  110  may include a radio frequency receiver. The radio frequency receiver may receive outputs from the electrodes using a radio frequency communication path. 
     The output of the receiver/instrument amplifier  110  is fed to a band pass filter  120 . The band pass filter  120  is designed to filter out high and low frequency signals and noise and to pass frequencies on the order of 100 Hz, for example. 
     The output of the band pass filter  120  passes to an amplifier and gain adjustment module  130 . The amplifier and gain adjustment module  130  includes an adjustable gain setting that is operated using the switch  103  shown in FIG. 1 a . Using the gain setting, the human subject is able to set a variable threshold for activation of a speaker in the apparatus  100 . The amplifier and gain adjustment module  130  also provides amplification of the voltage signal from the electrodes. 
     The output of the amplifier and gain adjust module  130  is fed to an integrator/ rectifier  140 . The integrator/rectifier  140  integrates the voltage signal when a certain voltage level is reached. The integrator/rectifier  140  also rectifies the voltage from AC to DC. The output of the integrator/rectifier  140  is passed to a comparator  150 . The comparator  150  compares the integrated output of the integrator/rectifier  140  to a preset value, and when the preset value is exceeded, the integrator/regulator  140  causes an output signal to be generated at the comparator  150 . The output signal from the comparator  150  is provided to a speaker circuit  170 . The speaker circuit  170  includes a small speaker (not shown in FIG. 3) that provides a steady output signal when the threshold value set at the amplifier and gain adjust module  130  is exceeded. Finally, the apparatus  100  shown in FIG. 3 includes a power supply  160  that supplies power to the electronics. The power supply  160  may be a small DC power supply, such as a 9 volt battery, for example. 
     FIG. 4 is an electrical schematic showing the control and display circuitry of the apparatus of FIG. 1 a . The electronics shown in FIG. 3 are grouped according to the block diagram components shown in FIG.  3 . The electronics shown in FIG. 4 are well known devices that need not be explained in detail here. Various other arrangements and capacities of the electronics other than those shown in FIG. 4 may be used to produce a desired output. As shown in FIG. 4, outer electrode inputs are connected to the receiver/instrument amplifier  110 , specifically to operational amplifiers  201  and  202 . A center electrode input is shown grounded. A summing operational amplifier  203  measures the signal differences between the three electrode inputs. 
     The band pass filter  120  comprises a number of operational amplifiers that provide both high frequency and low frequency filtering. The schematic shown in FIG. 4 shows one arrangement of these operational amplifiers. The amplifier and gain adjust module  130  comprises an operational amplifier  211  and a gain adjust resister  210 . The gain adjust resister  210  is operated by operation of the threshold switch  103  shown in FIG. 1 a.    
     The integrator/rectifier  140  comprises operational amplifiers  212  and  214  and rectifier assembly  216 . The rectifier assembly  216  converts AC voltage from the electrodes to DC voltage and the operational amplifiers  211  and  214  operate to integrate the output of the amplifier and gain adjust module  130  when the signal reaches a specified threshold value. 
     The comparator  150  includes an operational amplifier  224  and a charging capacitor  222 . The capacitor  222  is charged by the output of the integrator/rectifier  140 . The rate of charge of the capacitor  222  is determined by the integrated voltage out of the integrator/rectifier  140 . The output of the operational amplifier  224  changes based on the state of the detected voltage, causing the capacitor  222  to discharge. The output of the capacitor  222  is fed to the speaker circuit  170 . The speaker circuit  170  includes a speaker  228 , a speaker volume control  226  and a transistor  232 . The transistor  232  switches state to cause a clicking sound that is displayed by the speaker  228  at a rate determined by the measured voltage difference between the electrodes. The volume control  226  is used to adjust the volume displayed by the speaker  228 . 
     FIG. 5 is an electrical schematic of the power supply  160  shown in FIG.  3 . The power supply  160  may include a nine volt battery  230 , an on/off switch  233  and a negative voltage converter  234 . The power supply  160  provides DC power at between 1 and 9 VDC to selected components in the apparatus  100 . 
     In operation, the apparatus  100  of FIG. 3 produces a steady clicking sound, or similar audible feature indicating that a preset threshold value, indicative of a human subject&#39;s stress tolerance level has been exceeded. The apparatus  100  is placed is operation by first selecting a muscle group to which the electrodes are attached. The electrodes may be attached by any conventional attachment mechanism. Wires leading from the electrodes are coupled through wiring harness  102  shown in FIG. 1 a  to the instrument electronics. The apparatus  100  is turned on by placing the on/off switch  102  in the on position. The volume switch  102  is then operated to select a desired volume for output of the speaker  228 . Finally, the human subject selects a threshold value by which operation of the apparatus  100  will occur by operating the switch  103  shown in FIG. 1 a.    
     The apparatus  100  will then monitor voltage signals emanating from the muscle group selected by the human subject. When the differential voltage level reaches a certain value indicating that tension and stress have reached the threshold level, the apparatus  100 , through the speaker plate  105 , will display an audible signal. The human subject may then take actions to reduce the stress, while leaving the apparatus  100  connected and in operation. For example, the human subject may cease the activities that are causing the stress, such as typing, reading or other work related functions, or may relax certain parts of the body until the signal is reduced or stops. 
     By selecting an appropriate muscle group and an appropriate threshold setting, the human subject can learn to determine the onset of tension and stress and take actions to avoid the harmful effects by changing or moderating the behavior that leads to the stress. After repeatedly using the apparatus  100 , the human subject can learn to become aware of the onset of stress without the use of the apparatus  100 . The human subject may use the apparatus  100  continually for five work days, for example, to determine which work-related activities lead to a stress buildup. The human subject may learn that typing or keyboarding for more than two hours leads to stress buildup, as indicated by an output of the apparatus  100 . The human subject could then limit typing or keyboarding sessions to less than two hours to avoid a stress condition. In the same manner, the human subject will be able to control other behavior that leads to stress so as to keep stress levels at the very minimum. 
     The apparatus  100  provides a convenient and portable mechanism for detecting stress and for providing an easily controllable signal that the human subject can interpret to indicate the onset of stress. The apparatus  100  can be easily adjusted to accommodate different individuals. In addition, the apparatus  100  is convenient to use in ambulatory settings, including in most work environments. The apparatus  100  has a low profile and may easily fit into a pocket of the human subject&#39;s clothing, may be attached by a velcro fastener, or may clip on, for example. The apparatus  100  comprises simple electronics that are inexpensive to produce and that can be operated without extensive training and skill.