Abstract:
A resuscitation simulator includes a chest wall which moves back and forth along a compression path and a distance sensor as described for the invention which measures the optical path length between a transmitter and a receiver. The optical path length is determined by the position of the chest wall along the compression path. This enables the simple determination of the compression depth during reanimation training by measuring the optical path length and furnishes feedback to the person undergoing training in respect of the quality of the cardiac massages performed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. 119 to German utility model patent application DE 20 2014 102 161 U1, filed on May 9, 2014, which is relied upon and incorporated herein in its entirety by reference. 
       FIELD OF INVENTION 
       [0002]    The invention concerns a resuscitation simulator according to the generic character. 
       BACKGROUND OF THE INVENTION 
       [0003]    Resuscitation simulators in the form of human dummies for training cardiac resuscitation are well known. Resuscitation simulators serve to train reanimation techniques, in particular those utilizing cardiac massage in combination with artificial respiration. 
         [0004]    The correct performance of a cardiac massage, i.e. enhancing the probability of the patient&#39;s survival, requires considerable training, particularly in respect of the thoracic compression depth. In order to train the correct compression depth, until now the required feedback regarding the compression depth was entirely the responsibility of the person conducting the schooling. 
         [0005]    However, the information about the compression depths of the cardiac massages performed which present-day resuscitation simulators furnish is insufficient. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    It is therefore the purpose of the present invention to improve the resuscitation simulator described at the outset by being able to determine the compression depth more exactly. 
         [0007]    The resuscitation simulator described herein fulfills this purpose. 
         [0008]    The resuscitation simulator described has a chest wall which undergoes movement back and forth along a compression path and a distance sensor as described for the invention which measures the optical path length between a transmitter and a receiver. The optical path length is determined at least in part, and preferably entirely, by the position of the chest wall along the compression path. 
         [0009]    This enables the simple determination of the compression depth during reanimation training by measuring the optical path length and furnishes feedback to the person undergoing training in respect of the quality of the cardiac massages performed. 
         [0010]    Preferably, the transmitter emits radiation, the intensity of which diminishes with increasing path length. The receiver measures the incoming radiation intensity. From this measurement the optical path length, and therefore the compression depth, can be calculated. 
         [0011]    The transmitter is ideally an IR LED and/or the receiver also an IR LED. The use of radiative transmitters, in particular in the form of IR LEDs, enables the cost-effective integration of a distance sensor. This is essentially based upon the change in the optical path length of the IR radiation between the two IR LEDs, which in turn changes the measured intensity at the IR LED receiver, provided that the IR LED transmitter emits a constant radiation intensity. 
         [0012]    In a particularly preferred design of the resuscitation simulator the transmitter alternates between a switched-on and a switched-off state. In the switched-on state the transmitter generates radiation of constant intensity, and in the switched-off state the transmitter generates no radiation. In the switched-off state of the transmitter the receiver measures spurious radiation and converts this to a noise measurement signal which can be processed and temporarily stored in a microprocessor memory as required. In the switched-on state of the transmitter the receiver ideally measures the total radiation and converts this to a total measurement signal, which can be pre-processed and sent to the microprocessor. The microprocessor incorporates an algorithm according to which the actual useful measurement signal can be derived from the total measurement signal and the previously stored noise signal. This signal is then available for further pre-processing and evaluation. 
         [0013]    The useful measurement signal serves as the basis for the calculation of the optical path length traversed by the radiation and therefore for the calculation of the compression depth of the chest wall which the person training produces. 
         [0014]    Preferably, the distance sensor is comprised of a mushroom pushbutton switch which moves back and forth along the compression path, with the position of the outside fixed to the chest wall and the inside having a reflection plane, situated opposite the transmitter and the receiver. The optical path length is determined by the distance between the transmitter and reflection plane and between the reflection plane and receiver. This allows the simple mechanical construction of the distance sensor. 
         [0015]    In a particularly preferred design of the invention the transmitter is comprised of an IR LED connected by an electrical conducting path to a collector of a transistor in the common emitter state, while the base current of the transistor can be switched on and off. The operating point of the transistor can be set in the known manner via three fixed resistances. A voltage divider provided at the base of the transistor is preferably driven from a constant voltage source which can be switched on and off. Switching the voltage source on and off essentially generates a square wave signal through the IR LED which the receiver picks up. 
         [0016]    Ideally, the receiver comprises an IR LED, connected to a constant voltage source and in series with a measuring shunt, and a measurement signal tap for obtaining a measurement signal. By receiving IR light, the IR LED generates a leakage current. The leakage current arises due to a weak photovoltaic effect produced by the IR radiation impinging upon the receiver. The voltage drop produced by the leakage current at the measuring shunt is available to a signal pre-processing circuit. 
         [0017]    In a particularly preferred design the signal pre-processing circuit comprises an amplifier circuit, ideally in the form of a non-inverting first operational amplifier which amplifies the measurement signal from the receiver and is connected to the first input of a summer. Ideally, a second operational amplifier is connected as the summer. The summer subtracts a reference voltage from the amplified measurement signal. As a result of amplification, the fluctuations of the measurement signal are in a voltage range in which a normal microprocessor is not controlled. The voltage must therefore be shifted to a suitable range. Ideally, this shift of the voltage range is achieved with an offset compensation circuit acting together with the signal pre-processing circuit. The offset compensation circuit generates the reference voltage supplied to the summer together with the amplified measurement signal. 
         [0018]    The offset compensation circuit ideally has a third operational amplifier connected as a voltage follower. The voltage follower provides a loadable intermediate reference voltage without amplification. The intermediate reference voltage is supplied to a fourth operational amplifier connected as a non-inverting amplifier, and the intermediate reference voltage is amplified to the required reference voltage. The output of the fourth operational amplifier is connected to the second input of the second operational amplifier functioning as a summer. The variable pre-processed measurement signal at the output of the summer is then in a voltage range which the microprocessor can evaluate. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    The invention is described with the help of a design example, in six figures. 
           [0020]      FIG. 1   a  shows a schematic sectional view of the resuscitation simulator in accordance with the invention described. 
           [0021]      FIG. 1   b  shows a perspective view of the compression module in  FIG. 1 . 
           [0022]      FIG. 2  shows the IR transmitter circuitry. 
           [0023]      FIG. 3  shows the IR receiver circuitry. 
           [0024]      FIG. 4   a  shows the signal pre-processing circuitry of the amplifier circuit for the measurement signal from the IR sensor. 
           [0025]      FIG. 4   b  shows the offset compensation circuitry of the amplifier circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In accordance with the resuscitation guidelines of the European Resuscitation Councils (ERC), for the basic measures of the general procedure for the resuscitation of a patient a ratio of 30 cardiac massages to two artificial respiration phases is recommended. The resuscitation simulator  1  described here includes a built-in compression module  3  for training the cardiac massages. The compression module  3  is also illustrated in  FIG. 1   b . Further modular components are also included with the resuscitation simulator  1 , which in the interest of simplicity are not shown here and which are concerned, for example, with insufflation. The figures are not true to scale. 
         [0027]      FIG. 1   a  shows the resuscitation simulator  1  described, in the form of a human. The resuscitation simulator  1  has a chest wall  2  which moves back and forth along the compression path indicated by a double arrow. The resuscitation simulator  1  is suited for training cardiac massages. 
         [0028]    The chest wall  2  can be compressed along the displacement path by overcoming a counteracting spring  13  force. The counterforce corresponds roughly to the counterforce of an average adult thorax which must be overcome during cardiac massage. 
         [0029]    The ERC guidelines mentioned above recommend a maximum compression depth of 6 cm. However, compression depths less than 4 cm are also not recommended. Consequently, a compression depth of 4 to 6 cm is advisable for an adult person in order to achieve the maximum resuscitation probability. 
         [0030]    The resuscitation simulator  1  described serves to train the compression depth by means of a distance sensor  4 , comprising an IR LED  2  transmitter  6  and an IR LED  1  receiver  7 , which optimally measures the length of the IR radiation path between the IR transmitter  6  and the IR receiver  7  on the basis of one of the optical IR radiation paths. 
         [0031]    The resuscitation simulator  1  is shown in  FIG. 1   a  with the rear face  8  of the compression module  3  lying flat on a permanent base  9 . The helper presses with the flat hand on the outside of the chest wall  2  in the direction of the fixed base by pushing the mushroom pushbutton switch  10  of the compression module  3  against the spring  13 . The chest wall  2  is elastic in order to be able to move with the compression movement. 
         [0032]      FIG. 1   b  shows the function of the compression module  3 . The inside of the chest wall  2  lies on the pressure-resistant outside  11  of the mushroom pushbutton switch  10 . The mushroom pushbutton switch  10  is painted white on the inner side, facing the IR transmitter  6  and the IR receiver  7 , and thus forms a reflection plane  12  for IR radiation. The mushroom pushbutton switch has a hollow shaft. The spring  13  which generates the counterforce for the helper&#39;s compression movement is located in the shaft. 
         [0033]    The reflection plane  12  reflects the IR beam from the IR transmitter  6  and deflects the beam to the IR receiver  7 . As a result of the compression movement the mushroom pushbutton switch  10  moves up and down along the compression path. The optical path length l between the IR transmitter  6  and the IR receiver  7  changes according to the position of the reflection plane  12  along the compression path. The IR transmitter  6  emits an infrared signal, the intensity of which changes inversely with the square of the distance from the IR transmitter  6 . The IR receiver  7  picks up the signal and generates a measurement signal in the IR receiver  7 , the intensity of which is a function of the IR radiation received. 
         [0034]    As a rule, the IR radiation impinging upon the IR receiver  7  includes noise components, such as daylight or—in particular—emission from fluorescent lamps, which also emit radiation in the IR range. In order to enable an exact measurement of the optical path length l between the IR transmitter  6  and the IR receiver  7  it is necessary to correct the signal measures at the IR receiver  7  for the noise sources. 
         [0035]    For this purpose the IR transmitter  6  is switched on after 20 ms and after a further 20 ms switched off again, while the IR receiver  7  continuously measures the IR radiation. The IR radiation received generates a total measurement signal which, with the IR transmitter  6  switched on, is comprised of a noise measurement signal superimposed over the useful signal and, with the IR transmitter  6  switched off, only the measured noise signal is measured at the IR receiver  7 . The useful measurement signal employed is essentially determined as the difference of the total measured signal and the measured noise signal 
         [0036]      FIG. 2  is a schematic illustration of the IR transmitter  6 . The IR LED  2  is connected to the collector of a transistor T operating in common emitter mode. The operating point of the transistor T is set from three fixed resistances R 1 , R 2 , R 4 . The base of the transistor T is connected via one of the two resistances R 1 , R 2  to a current source IR_EN which can be switched on and off. The current through the voltage divider R 1 , R 2  is switched on after 20 ms and switched off again after a further 20 ms. As a result the IR LED  2  generates a roughly square wave radiation profile. 
         [0037]      FIG. 3  shows the circuitry for the IR receiver  7 , comprising the IR LED  1 . The IR LED  1  is in series with a 1 MΩ measuring shunt R 31 . As a result of receiving infrared radiation, the IR LED  1  generates a photocurrent in the IR receiver  7 . The voltage drop across the measuring shunt  31  is pre-processed in the amplifier circuitry as shown in  FIG. 4   a  and  FIG. 4   b  and is available at the output IR_SEN_ADC. 
         [0038]      FIGS. 4   a  and  4   b  must be read together. Together they represent the amplifier circuit, comprised of the signal pre-processing circuitry shown in  FIG. 4   a , as is seen in the left part of the circuit, which measures and pre-processes the measuring shunt R 31 . Pre-processing takes place by a non-inverting first operational amplifier U 2 B, shown here with an amplification factor of V U =1+(R 11 /R 14 )=50. The amplified signal is then sent via a resistance R 12  to a second operational amplifier U 2 C which functions as a summer. 
         [0039]    In  FIG. 4   a  and  FIG. 4   b  the terminals to be connected are marked in the same manner. In particular, the output of a fourth operational amplifier U 2 A is connected via a resistance R 18  to the negative input of the second operational amplifier U 2 C. 
         [0040]    The offset compensation circuit of  FIG. 4   b  serves to shift the signal available at the output IR_SEN_ADC to a voltage range from 0 to 3.3 Volts, as this is the operating range of the microprocessor connected to the IR_SEN_ADC. The offset compensation circuit has a third operational amplifier U 2 D and the fourth operational amplifier U 2 A, with the third operational amplifier U 2 D functioning as a voltage follower which generates a reference voltage URef  1 =UVCC×(R 3 /(R 3 +R 7 ))=2.1 Volts when the voltage UVCC on the voltage divider R 3 , R 7 =3.3 Volts, as shown in  FIG. 4   b . The voltage follower provides the non-amplified reference voltage of 2.1 Volts to the positive input of the fourth operational U 2 A. The fourth operational amplifier U 2 A is operated as a non-inverting amplifier with the amplification factor V U =1+(R 30 /R 17 )=4. The third operational amplifier U 2 D and fourth operational amplifier U 2 A together therefore generate a reference voltage of VCC_REF=8.4 Volts. This voltage corresponds exactly to the required offset compensation voltage. The reference voltage VCC_REF is sent to the second operational amplifier U 2 C, functioning as a sum amplifier with amplification V U =1, and extracts the reference voltage of 8.4 Volts from the amplified sensor signal. In this way a pre-processed measurement signal is developed in the voltage range from 0 to 3.3 Volts. This pre-processed sensor signal IR_SEN_ADC is first digitized by the analog-digital converter and then sent to the microprocessor (not shown) for further processing. 
         [0041]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principals and applications of the present invention. Accordingly, while the invention has been described with reference to the structures and processes disclosed, it is not confined to the details set forth, but is intended to cover such modifications or changes as may fall within the scope of the following claims. 
       FIGURE REFERENCES 
       [0000]    
       
           1  Resuscitation simulator 
           2  Chest wall 
           3  Compression module 
           4  Distance sensor 
           6  IR transmitter 
           7  IR receiver 
           8  Rear face of the compression module 
           9  Fixed base 
           10  Mushroom pushbutton switch 
           11  Outside of the mushroom pushbutton switch 
           12  Reflection plane 
           13  Spring 
         l Optical path