Abstract:
A method and apparatus is disclosed for slow wave sleep improvement. The method includes recording a biosignal from a skin area of a patient using an electrode system. The slow wave stage of NREM sleep is detected by analyzing an oscillation rate of the biosignal. If the slow wave stage is detected, threshold electrocutaneous stimulation is applied to improve the quality of sleep. The described embodiment relates to an apparatus for slow wave sleep improvement comprising an electrode system, a measuring unit, a therapy unit and a processor. The processor is coupled to the measurement unit for receiving the biosignal corresponding to the electrodermal activity. The processor proceses the biosignal to determine the slow wave sleep stage and activates the therapy unit to deliver threshold electrocuteneous therapy to the patient with the purpose of improving the slow wave sleep stage.

Description:
BACKGROUND 
       [0001]    Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. Sleep architecture refers to the basic structural organization of normal sleep. 
         [0002]    There are two distinct states that alternate in 90 minute cycles and reflect differing levels of brain activity. Each sleep cycle consists of non-rapid eye movement (NREM) and rapid eye movement (REM) activities, both states repeat over and over again during a night&#39;s sleep. NREM sleep is further subdivided into four stages. Each state is characterized by a different type of brain wave. 
         [0003]    Stage N1 is of light sleep, which is considered a transition between wakefulness and sleep and usually accounts for 5-10% of total sleep time. This stage is characterized by alpha brain waves having a frequency 8-13 Hz. An individual can be easily awakened during this period. 
         [0004]    Stage N2 occurs throughout the sleep period and represents 40-50% of the total sleep time. This stage is characterized by theta brain waves ranging from 4 to 8 Hz. During stage N2, brain waves slow down with occasional bursts of rapid waves. 
         [0005]    Stages III and IV are distinguished from each other only by the percentage of delta wave activity with a frequency oscillation between 0 and 4 Hz. Together these two stages represent up to 20% of total sleep time. Stages N3 and N4 represent deep sleep, during which all eye and muscle movement ceases. It is difficult to wake up an individual during these 2 stages; these have been combined by the American Academy of Sleep Medicine as stage N3 and are called slow wave or delta sleep. Slow wave sleep provides the most recuperative effect and defines the quality of sleep. 
       SUMMARY 
       [0006]    According to a method described herein, the slow wave sleep stage of a patient is improved by detecting slow wave sleep stage and employing gentle, subthreshold electrocutaneous stimulation. Furthermore, the disclosed method and apparatus permit adjustment of the stimulation schedule, prolonging the slow wave sleep stage by preventing the patient from sub-awakening during the slow wave sleep stage. Further details and embodiments are discussed below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a functional block diagram illustrating components of an example threshold electrocutaneous stimulation apparatus that improves sleep architecture of patient. 
           [0008]      FIG. 2  shows flow diagrams illustrating example technique for operating the apparatus in the idle mode. 
           [0009]      FIG. 3  shows flow diagrams illustrating example technique for operating the apparatus in the active mode. 
           [0010]      FIG. 4  shows flow diagrams illustrating example techniques for threshold electrocutaneous stimulation therapy delivery to a patient. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    A threshold electrocutaneous stimulation (TES) apparatus  10  that improves slow wave sleep stage of patient is shown schematically in  FIG. 1 . TES apparatus  10  includes measuring unit (MU)  12 , therapy unit (TU)  20  and processer  18 . In the example shown in  FIG. 1 , MU  12  includes an electrode system of eight skin electrodes  16  that are used to register the electrodermal activity (EDA) signal and apply subthreshold electrocutaneous stimulation. The MU  12  further includes an EDA signal receiver  14 , which incorporates an electronic switch and amplifier (not shown). The electronic switch selectively connects each of 4 pairs of electrodes  16  to the amplifier for amplification of the EDA signal. The amplified signals are sent to an A/D converter for converting the analog EDA signal to a digital signal, which is sent to the processor  18  for analysis. 
         [0012]    The TU  20  incorporates an electric pulse generator  22  for generating electric pulses and an electric pulse control module  24  for changing pulse parameters to deliver different schedules of subtreshold electrocutaneous stimulation therapy to the patient. The electric pulse generator  22  is controlled by the processor  18 . 
         [0013]    The processor  18  analyses the EDA signal and establishes whether the patient is in a slow wave sleep stage by determining the oscillation rate of the EDA signal. The processor  18  operates the TU  20  by switching on the pulse generator  22  in the onset of the slow wave sleep stage and then terminating the stimulation in the end of the slow wave stage. TES apparatus  10  also includes a replaceable power source  26  which is regulated by processor  18 . 
         [0014]    The TES apparatus  10  may be incorporated into a palm-sized (e.g. 2″×3″) device connected to an adjustable band to position the electrodes  16  into contact with the skin on the user&#39;s palm, wrist, arm, etc. 
         [0015]    The apparatus  10  has three functional modes: idle, active and stimulation. 
         [0016]    In the idle mode, the operational flow diagram of which is shown in  FIG. 2 , the processor  18  measures the skin resistance value R between each of 4 pairs of skin electrodes  16  in step  50 . The processor  18  repeats the measurements every 5 seconds and compares the measured resistance value R to an R threshold value (e.g. 1 megohm) in step  52 . In step  54 , if the measured resistance value R is ≧R threshold value, the TES apparatus  10  remains in the idle mode with lowered power consumption in step  56 . If the resistance value R is ≦R threshold value in step  54 , that indicates that the galvanic contact between the skin and electrodes  16  ( FIG. 1 ) is formed and the TES apparatus  10  switches to the active mode. 
         [0017]    The operational flow diagram of the active mode is shown in  FIG. 3 . In the active mode, the TES apparatus  10  measures the resistance value R between each of 4 pairs of skin electrodes  16  with a frequency of 10 Hz in step  60  and compares the resistance values R to a R threshold value in step  62 . If the resistance value R between each of 4 pairs of skin electrodes remains ≦R threshold value in step  64 , the EDA signal is analyzed by counting the number of oscillations N for every 60 second period in step  68 . When the number of EDA signal oscillations reaches the rate of N threshold of 6 for a 60 second period in step  70 , the TES apparatus  10  switches in the stimulation mode, otherwise the TES apparatus  10  keeps counting the number of EDA signal oscillations N for every 60 second period. If the resistance value R between any of 4 pairs of skin electrodes becomes ≧R threshold value, the TES apparatus  10  switches in the idle mode with a lowered power consumption. 
         [0018]    In the stimulation mode the rectangular electric pulses are concurrently applied to each of 4 pairs of skin electrodes  16  ( FIG. 1 ) in step  72 . For example, the pulse current may be 100 microamps, pulse duration 10 milliseconds and pulse duty cycle  10 ̂-2%. The electric stimulation period may last 30 seconds (for example). Afterwards, the stimulation pauses and the TES apparatus  10  switches into the pause measurement mode for 30 seconds, during which EDA signal is analyzed by counting the number of oscillations in step  74  and the resistance value R between each of 4 pairs of skin electrodes  16  is compared to the resistance values R to a R threshold value in step  76 . If during the pause measurement mode the number of EDA signal oscillations N is ≧Np threshold value (such as 3) and the resistance value R between each of 4 pairs of skin electrodes remains ≦R threshold value, the TES apparatus  10  resumes electric stimulation of the patient in step  78 . If the resistance value R between any of 4 pairs of skin electrodes becomes ≧R threshold value, the TES apparatus  10  switches in the idle mode with a lowered power consumption in step  80 . If the number of EDA signal oscillations N is &lt;Np threshold value of 3 (for example), the electric stimulation is terminated and TES apparatus  10  switches to the active mode in step  82 . The Np threshold value could be between 0.5 to 20 oscillations per minute but is preferably between 3 to 10 oscillations per minute). 
         [0019]    The subtreshold electrocutaneous stimulation therapy may include applying a rectangular pulse train or a rectangular pulse packet train to the skin area of the patient via the electrodes  16  ( FIG. 1 ). The frequency of the rectangular pulse train may be between 0.1 Hz to 10 Hz. The frequency of the rectangular pulse train more preferably may be between 0.5 to 5 Hz. The frequency of the rectangular pulse packet train may be 0.1 Hz to 10 Hz. The frequency of the rectangular pulse packet envelope train more preferably may be between 0.5 to 5 Hz. 
         [0020]    A rectangular pulse packet train comprises rectangular pulse packets. Each pulse packet comprises a series of rectangular pulses with identical frequency within the range of 500 Hz to 5,000 Hz. More preferably, the frequency may be in the range of 1,000 to 3,000 Hz. Each pulse packet may include a series of pulses with a given frequency distribution around a central frequency f. The series of rectangular pulses may have a desired frequency distribution within the pulse packet, such as Gaussian, Poisson, or Lorentz distribution. 
         [0021]    The rectangular pulse train may include pulses in monopolar (unipolar), bipolar or combined unipolar-bipolar fashion. The rectangular pulse train parameters may include pulse amplitudes between 1 to 1,000 microamperes, more preferably from 50 to 500 microamperes, pulse durations between 1 to 500 milliseconds, more preferably from 1 to 100 milliseconds, and pulse periods between 0.1 to 3 seconds, more preferably from 0.5 to 1.5 seconds. 
         [0022]    The rectangular pulse packet train may include pulse packets in monopolar (unipolar), bipolar or combined unipolar-bipolar fashion. The rectangular pulse packet train parameters include pulse packet amplitudes between 50 to 500 microamperes, pulse packet durations between 1 to 100 milliseconds, and pulse packet periods between 0.5 to 1.5 seconds. 
         [0023]    A flow diagram illustrating an example technique for subthreshold electrocutaneous stimulation therapy delivery to a patient is shown in  FIG. 4 . The biosignal (EDA signal) from skin electrodes  16  ( FIG. 1 ) is received in step  82 . The conductive quality of skin electrodes-skin junctions is verified in step  84 . The oscillation rate of the biosignal is established in step  86 . The slow wave sleep stage onset is detected in step  88 . The electrostimulation therapy is then applied in step  90  upon the detection of the slow wave sleep stage onset in step  88 . The electrostimulation therapy is applied during the slow wave sleep stage, until the slow wave stage end is detected in step  92 . After that the electrostimulation therapy will resume only after the onset of the next slow wave sleep stage is detected. 
         [0024]    The TES apparatus  10  may also include short-range wireless connectivity such as Bluetooth and/or Wi-Fi, for connecting to the user&#39;s device (e.g. smartphone, tablet, computer, docking station, etc). The TES apparatus  10  gathers information regarding the user&#39;s sleep patterns and sends this information to an app on the user&#39;s device. The app on the user&#39;s device can display the various sleep stages for each night&#39;s sleep, including the beginning and end times for each stage and the total and/or percentage time spent in each stage. The user may also send commands to the TES apparatus  10  with the app and device, such as adjusting different parameters, updating firmware, selectively disabling off the active mode (but continuing to monitor sleep stages), etc. 
         [0025]    In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.