Abstract:
A monitoring apparatus ( 4 ) monitors a user&#39;s heart rate and/or heart rate variation. The apparatus includes a capacitor ( 22 ) which is positionable on or near a body part of a person, for example a person&#39;s limb, for example an arm ( 3 ), such that an electrical capacitance of the capacitor ( 22 ) is influenced by blood pressure pulses of blood running through the body part. The apparatus ( 4 ) also includes a data processor ( 26 ) for determining the heart rate and/or heart rate variation from changes in the capacitance of the capacitor ( 22 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a monitoring apparatus for monitoring a user&#39;s heart rate and/or heart rate variation. 
     Apparatuses for monitoring a user&#39;s heart rate and/or heart rate variation generally have a medical use, such as for determining the occurrence of a heart failure and/or the possibility of occurrence a heart failure. 
     Also such apparatuses are used by athletes, for example in a training scheme. 
     BACKGROUND OF THE INVENTION 
     A monitoring apparatus is known from American patent specification U.S. Pat. No. 3,838,684. The monitoring apparatus comprises a pressure sensitive sensor, which during use abuts a part of a skin surface for measuring the heart rate. The pressure pulses obtained by the sensor are converted to an electrical pulse. Furthermore, a light source is provided which allows a user to count the light pulses representative of each heart beat during a 15 second interval to thereby determine visually what his heart rate is at any given time. The apparatus is compact and strapped about the wrist. 
     A disadvantage of the known monitoring apparatus is its unreliability, because in order to obtain good heart rate measurements, the pressure sensor is required to be located exactly on a position adjacent to a blood vessel from which the measurements are to be obtained. Therefore, the apparatus is not suitable for use by athletes who prefer to use the apparatus while running, jumping and/or moving in any other manner. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to address the disadvantages mentioned above. 
     According to the present invention, a monitoring apparatus for monitoring a user&#39;s heart rate and/or heart rate variation, the apparatus comprising: a capacitor having at least two capacitor electrodes, wherein the capacitor electrodes are position able adjacent to different surface parts of a body part of a person, the body part being for example a person&#39;s limb, for example an arm, such that an electrical capacitance of the capacitor is influenced by blood pressure pulses of blood running through the body part, wherein the apparatus further comprises a data processor for determining the heart rate and/or heart rate variation from changes in the capacitance of the capacitor. 
     Surprisingly, it is possible to measure a person&#39;s heart beat by using a capacitor having capacitor electrodes which are located adjacent to different surface parts the person&#39;s body part. As a result of the pressure pulses running through the blood vessel, the capacitance is influenced. Due to capacity changes it is possible to determine the occurrence of heartbeats. 
     Preferably, in order to obtain accurate measurements, the different surfaces are located at substantially opposite sides of the person&#39;s body part, particularly such that the body part extends between the electrodes during use. 
     In order to facilitate the possibility for a user to read measurements of his own heart rate, a preferred embodiment of the apparatus comprises an output device for auditively and/or visually making knowable to the user the heart rate and/or heart rate variation determined by the data processor. 
     In an embodiment of the apparatus according to the present invention, the apparatus comprises an oscillator for sending an oscillating signal through the capacitor to be able adequately determines capacity changes. 
     Preferably the oscillator is arranged to generate a binary signal. An advantage of a binary signal is that in the data processor no further A/D-converter is necessary. 
     To be able to determine changes in frequency, the data processor of a further embodiment of the apparatus according to the present invention comprises a one shot unit for generating a pulse train, wherein the pulse train is formed by pulses generated by the one shot unit in response to an up going flank or a down going flank in the oscillating signal. In such an embodiment, the data processor may comprise an averaging unit for generating a moving average of the pulse train, the moving average being indicative of a frequency changes of the oscillating signal. 
     In an advanced embodiment of the apparatus according to the present invention an accelerometer is provided for determining acceleration of the body part. If the acceleration of body part is known while monitoring the heart rate and/or heart rate variation, it is possible to compensate for any interference and/or disturbance occurring as a result of the acceleration. 
     To suitably implement the compensation for the interference or the disturbance, the data processor can be arranged for determining an estimation of a disturbance value in measurements which value has been caused by the acceleration of the limb. 
     A basic idea of the present invention is to use only a single wristband, particularly a wristwatch, having simple means to monitor the user&#39;s heart, without using for example a chest band. Herein, preferably, the single wristband comprising the capacitor having the at least two capacitor electrodes preferably also comprises the data processor, and more particularly also comprises the output device 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment described hereinafter with reference to the accompanying drawing, wherein same reference signs refer to corresponding reference parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is a perspective view of a first embodiment of the apparatus according to the present invention; 
         FIG. 2  is a top view of the apparatus shown in  FIG. 1 ; 
         FIG. 3  is a schematic of a data processor, as comprised in the apparatus of  FIGS. 1 and 2 ; 
         FIG. 4  is a top view of a modification of the apparatus shown in  FIGS. 1 and 2 ; and 
         FIG. 5  is a top view of a second embodiment of the apparatus according to the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a hand  1  and a wrist  2  of an arm  3  of a person who is using a first embodiment of a monitoring apparatus  4 . Referring to  FIG. 2 , the apparatus  4  comprises a housing  6  having a time display  8  with two pointers  10  and  12 , and a wrist band having a first strap part  14  and a second strap part  16 . The apparatus is configured to provide an electrical capacitor  22 , having electrodes  18 ,  20 . Each of the strap parts  14 ,  16  is provided with a capacitor electrode  18 ,  20  in the form of a plate  18 ,  20 , together forming the capacitor  22  during use, when the apparatus is carried by a user. The capacitor plates can be positioned adjacent to different surface parts. In the embodiments shown, the surface parts are located on substantially opposite sides of the arm  3  when in use, that is, on sides of arm  3  that are substantially faced away from each other. 
     The electrodes  18  and  20  are electrically coupled to an oscillator  24 , which, in operation, sends a periodic, electrical signal through the capacitor  22 . The apparatus  4  further comprises a data processor  26  for determining the heart rate and/or heart rate variation from changes in the capacitance of the capacitor. Also, the apparatus  4  comprises an output device  28  for auditively and/or visually making knowable to the user the heart rate and/or heart rate variation determined by the data processor  26 . In  FIG. 2 , the output device  28  is formed by a visual display  30 . 
     The data processor  26  preferably comprises a frequency detector. Many kinds of frequency detectors are suitable for use in the data processor  26 . However, in this specific embodiment (see  FIG. 3 ), frequency detector of the data processor  26  of the apparatus  4  comprises a converter  32  for converting the periodic signal to a binary signal. In this specific embodiment the converter is a comparator with an output which is a logical one if the input is &gt;0 and which output is a logical zero if the input is &lt;0. However, other kinds of suitable converters may be employed. The frequency detector further comprises a one shot unit  34  for generating a pulse train B as an exit signal in response to a change in signal value of the binary signal and an averaging unit  36  for generating a moving average &lt;B&gt; of the pulse train B generated by the one shot unit  34 . In order to avoid the necessity of the converter  32  an oscillator can be provided arranged to generate a binary signal, such as a block signal. As a single pulse generated by the one shot unit  34  has a fixed time length and the pulse is generated only in response to a change in the signal value of the exit signal, the moving average value generated by the averaging unit  36  is indicative of the frequency of the binary signal. Based on this moving average signal, the calculating unit  38  can calculate the heart rate and/or heart rate variations. 
     An athlete using the apparatus  4  which, in this embodiment, is incorporated in a wrist watch, can, for instance while running, easily check his heart rate and/or variations therein by looking at his watch. If the heart rate becomes too high, the athlete can lower his effort in order to maintain a predetermined training scheme. 
     Alternatively, the apparatus  4  may be used while playing computer games. The heart rate and/or heart rate variations may be used as a parameter in computer games. The abilities of a computer game character to be controlled by the user of the apparatus may, for instance, be influenced by the heart rate of the user. 
     Another application is use of the apparatus, wherein the heart rate and/or heart rate variations are used to determine the occurrence of a heart failure and/or the possibility of occurrence of a heart failure. Upon the determination of a heart failure, the apparatus can be arranged to generate an alarm signal to an external receiver  40 . 
     A modification of the first embodiment is shown in  FIG. 4  in which an output device  28  is provided for auditively making knowable to the person the heart rate and/or heart rate variation. Instead of being formed by the visual display  30 , the output device  28  is formed by a socket  42  and an earpiece  44  having a wiring  46  and a plug  48 , which is arranged to be inserted in the socket  42 . In the modification of the first embodiment, the data processor  26  is arranged to periodically notify the person of his/her heart rate and/or heart rate variations by using sound, for instance a human voice. However, instead using the wiring  46  and the plug  48 , the earpiece  44  and the output device  28  may also be arranged to communicate in a wireless manner. 
       FIG. 5  schematically shows a second, more advanced embodiment of the apparatus. The second embodiment of the apparatus is similar to the first embodiment. However, in  FIG. 5  it can be seen that the second embodiment of the apparatus also comprises an accelerometer  50  for determining acceleration of the arm  3 . The accelerometer  50  determines an acceleration value of the arm  3 . The data processor  26  is suitably arranged for determining an estimation of a disturbance value in measurements in the at least one electrical parameter caused by the acceleration of the arm in order to be able to compensate for this disturbance. Furthermore, the accelerometer  50  may be arranged to recognize periodic patterns in the acceleration of the arm in order to even further increase the ability to compensate for the disturbance. 
     It will be clear to a person skilled in the art that the invention is not limited to the embodiments shown above. For instance, various data processors in addition to the data processors disclosed herein may be suitable for application without departing from the scope of the present invention as determined by the accompanying claims. 
     For example, a mentioned wristband can be configured in various ways, and can include for example one or more straps, and/or be arranged in a different way. Also, a mentioned capacitor, data processor, and/or output device can be coupled to a wristband in various ways, For example, the capacitor, data processor, and/or output device can be coupled to the wristband can be integrally connected to the wristband, can be detachably connectable thereto, be at least partly comprised in a housing of the wristband, and/or in a different manner. Also, the heart rate and/or heart rate variation may be stored in a memory comprised in, for instance, the data processor. Such embodiments are within the scope of the present invention as determined by the accompanying claims. 
     Owing to the invention, it is possible to easily measure a person&#39;s heart beat by using a capacitor in an unconventional manner. 
     It is noted that the word “comprising” does not exclude the presence other elements in an part of the apparatus or additional steps in a method. It is also noted that the word “a”/“an” does not exclude plurality. Furthermore, the reference signs in the claims are not to be construed as to limit the scope of the present invention.