Abstract:
A temporally and frequency controlled amplified cardiac stethoscope device is provided wherein frequency response selection is carried out by manually tuning two active filters thereby permitting user pass band (high and low frequency cutoff) selection. Simultaneously, the user is able to select a time window, or interval, of the audio output of the device for specific aural observation, to the exclusion of the remainder of cardiac cycle sounds. The device is miniaturized to permit transport in a clothing pocket and use in the clinic or at the bedside. The device is based upon electrocardiographic QRS complex/electronic Schmitt trigger synchronization of a sweep generator and comparator. The synchronization signal, in combination with manual user inputs, permits the control of digital/analog switching of on/off time intervals of a variable frequency response electronic stethoscope.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to stethoscopes and, more particularly, to an improved electronic cardiac stethoscope.  
         RELATED ART  
         [0002]    The stethoscope has undergone many varieties of modification since its invention in 1819. These modifications have typically been attempts to increase the ability to detect and interpret the frequently subtle physiologic sounds originating in the thorax. Most of these modifications have occurred since the availability of small electronic components.  
           [0003]    Numerous electronic stethoscopes have been proposed or developed over the past several decades. The predominant concept embodied by the majority of them has been one of controlled and variable amplification of physiologic sounds, e.g., U.S. Pat. No. 4,618,986, U.S. Pat. No. 4,170,717 and U.S. Pat. No. 4,438,772. Another concept in stethoscope improvement has been the effort in noise reduction or modification, e.g., U.S. Pat. No. 5,602,924 and U.S. Pat. No. 5,610,987. Another concept incorporated into electronic stethoscopes has been that of frequency response modification. Several means of shaping the frequency response have been demonstrated, e.g., U.S. Pat. No. 5,557,681, U.S. Pat. No. 4,821,327. U.S. Pat. No. 4,731,849 discloses a device which both shapes the frequency response and employs automatic gain control of a variable sound level. U.S. Pat. No. 4,792,145 discloses an electronic stethoscope that manipulates otherwise inaudible auscultated frequencies through the use of fast Fourier transformation and processing/translation.  
           [0004]    U.S. Pat. No. 5,003,605 discloses an electrocardiographic system used to produce an acoustic timing signal to assist in the determination of expected timing of heart sounds. U.S. Pat. No. 4,594,731 discloses a device which employs electrocardiogram signals to time control the modulation of modified phonocardiogram auditory signals.  
           [0005]    An attempt was made some time ago, as disclosed in U.S. Pat. No. 3,132,208, to provide an electronic stethoscope to enable “time-filtering” of physiologic sounds through the use of two adjustable transistor multi-vibrators which are periodically switched on or off. This system derives a control voltage from a prominent heart sound and with a ‘three’ rather than two lead electrocardiograph that does not permit compensation for varying body sizes and masses. The device suffers from potential false triggering of the time-filtering interval by the T-wave of the electrocardiogram or, potentially, a failure to trigger at all in an individual with low amplitude body surface potentials. This physically large device has no timing reference indicator or visible display and does not provide any frequency response processing or control. The device also requires numerous manual controls that can easily be mis-set and thus obviate correct functional control of the time-filtering in individuals with cardiac cycles of unusual length.  
           [0006]    U.S. Pat. No. 6,005,951 discloses an unsynchronized clock/oscillator employed to select which components of both normal and abnormal heart sounds to amplify.  
           [0007]    Recently, electronic stethoscopes have been disclosed that permit a visual display of auscultated sounds (U.S. Pat. No. 5,737,429) or permit automated analysis of auscultated sounds (U.S. Pat. No. 5,218,969).  
           [0008]    In spite of the above, the art of stethoscopy remains a challenging one in large part due to the great effort and time required to acquire the concentration and mental time windowing necessary to isolate and identify sometimes very brief and low amplitude physiologic sounds.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention obviates the need for much of the slowly acquired auscultatory skills referred to above by permitting the electronic selection of portions of the cardiac cycle to be amplified and tuned, and, subsequently, to be much more easily heard and identified. The invention also provides automatic compensation for cardiac size (by providing an automatic gain control to precisely determine triggering of each new cardiac cycle), and, potentially, the automatic determination of cardiac cycle length to further automate the auscultation process.  
           [0010]    It is an object of the invention to provide an electronic stethoscope that permits the selection of a time window during the cardiac cycle for selective variable amplification.  
           [0011]    Another object of the invention is to provide frequency windowing/band pass tuning of the phonocardiogram signal.  
           [0012]    Another object of the invention is to provide automatic processing of all necessary functions, except that of the operator selected time and frequency parameters.  
           [0013]    The invention relates, in general, to a miniaturized clinical device for frequency and time selective cardiac heart sound and peripheral vascular auscultation. The device permits detailed observation of single, individualized heart sounds or periods to the exclusion of all others, i.e., sounds such as normal heart sounds-S 1  and S 2 , adventitious heart sounds, and murmurs (pre-systolic, systolic, and diastolic). The invention also permits selective detailed observation of ejection sounds, rubs, clicks, snaps, heart-sound splitting, and bruits of the, e.g., carotid, aortic, and femoral arteries, etc. The invention further permits frequency tuning of the selected time interval of sound, thereby enabling the selection of only relevant components of the phonocardiogram signal.)  
           [0014]    Further features and advantages of the invention will be set forth in, or apparent from, the following detailed description of the preferred embodiments of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a block diagram of a preferred embodiment of the device of the invention;  
         [0016]    FIGS.  2  to  4 , taken together, constitute a schematic circuit diagram of the device of FIG. 1, in accordance with a preferred embodiment thereof.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    In the preferred embodiment of the invention shown in FIG. 1, the device or system includes an amplified electronic frequency-band selective stethoscope AS, and an electrocardiogram amplifier EA. The latter is connected through an electrocardiogram automatic gain control circuit GC, and a Schmitt trigger ST, to a sawtooth ramp/sweep oscillator SO. The output of sweep oscillator SO form one input to a variable/adjustable comparator circuit CC as well as an input to a light emitting diode (LED) driver and display array DA and to a “retrace” noise suppression (blanking) circuit BC. Comparator CC provides inputs an electronic time-window switching system or circuit SS and to blanking circuit BC.  
         [0018]    The device of FIG. 1 also includes a chest pickup and transducer PT and an output transducer and earpiece OT. A low frequency cutoff control circuit LC, a high frequency cutoff control circuit HC, and a volume control circuit VC form inputs to stethoscope AS while skin surface EKG pickup electrodes PG produce the input signals for amplifier EA. Time interval selection controls TC are provided for comparators CC and a width control circuit WC is provided for sweep oscillator SO.  
         [0019]    The operation of the device or system of FIG. 1 can be summarized as follows.  
         [0020]    The frequency selective stethoscope audio amplifier AS is inputted low level cardiovascular sounds by the pickup and transducer PT, and outputs its conditioned and controlled signal to the output transducer OT.  
         [0021]    Within the frequency selective stethoscope AS are two adjustable variable frequency response 2-pole VCVS active filters (not shown). The low pass filter control LC permits the selection of a high frequency cutoff of from 100 to 3000 Hertz. The high pass frequency filter control HC permits the selection of a low frequency cutoff of from 20 to 300 Hertz. The volume control VC permits user selection of a wide volume range of the desired time interval selection for observation.  
         [0022]    The electrocardiogram amplifier EA receives near millivolt cardiac skin surface potentials from electrodes PE. In this embodiment, amplifier EA consists of a 70 dB gain, 0.15 to 20 Hertz response system with an instrumentation amplifier front end.  
         [0023]    The electrocardiogram automatic gain control circuit GC maintains a near constant 2 volt output for the Schmitt trigger ST in spite of a 4× range of variation in patient skin surface potentials.  
         [0024]    The Schmitt trigger system ST converts a 0.8 volt or greater QRS complex into a “low” output to turn on and reset the sawtooth wave sweep oscillator SO.  
         [0025]    The sawtooth wave sweep oscillator SO performs two functions. First, it drives the comparator circuits CC. The comparator circuits CC, with inputs from both the sawtooth oscillator SO and two user adjustable slide potentiometers TC, select the time interval/window of the cardiac cycle to be aurally observed by controlling an electronic switch SS.  
         [0026]    Second, the sawtooth wave from oscillator SO drives the LED display system DA. The latter indicates to the user that the EKG complex has been captured, and indicates the duration of the sawtooth waveform so to permit user adjustment for a full width visual display through the use of the width control circuit WC.  
         [0027]    Ancillary circuitry, including the retrace blanking circuit BC, using a series of logic gates, buffers, inverters and differentiators in parallel with the comparator output, maintains an open signal path (as needed) during the down-stroke of the sawtooth wave. This prevents an artifactual noise impulse from being added during selected off periods of the user selected time window.  
         [0028]    The time window switching circuit SS is an electronic switch comprising a digitally controlled analog switch or gate, which opens and closes an audio signal path to alternately pass or block the electronic stethoscope audio signal.  
         [0029]    Referring now to FIGS. 2, 3 and  4 , a schematic circuit diagram of a preferred implementation of the device is shown in these figures.  
         [0030]    In FIG. 2, electrocardiographic lead I or II signals (from skin self-adhesive silver/silver chloride electrodes) are applied to operational amplifier inputs  1  and  2 . The differential signal is passed through isolation resistors  3  and  4  to instrumentation amplifier integrated circuits  10  and  11  and through resistors  12  and  13  to integrated circuit  15 . The ratios of resistors  7  to  8  and  16  to  12  determine the gain of the stages. Capacitor  17  and resistor  18  determine the low frequency cutoff of 0.15 Hertz and feed voltage follower integrated circuit  19 .  
         [0031]    This circuit feeds resistors  20  and  21 , and capacitors  22  and  23 , and unity gain operational amplifier  24 , which comprise a low pass filter with a 20 Hertz cutoff. This filter feeds a second duplicate filter stage composed of resistors  25  and  26 , capacitors  27  and  28 , and unity gain integrated circuit  29 . (The dual low pass filters, with a combined 12 dB per octave roll-off to suppress 60 Hertz ambient interference, permit EKG signal acquisition with only 2 input electrodes.) Capacitor  30  and resistor  31  form a 0.15 Hertz frequency cutoff high pass filter whose output is applied to the input of operational amplifier  32 . Resistor  33  and potentiometer  34  determine the gain of the amplifier stage.  
         [0032]    Capacitors  35  and  141  couple the pre-amplified electrocardiographic signal to integrated circuit  129  and a gate of MOSFET  135 , respectively, of the automatic gain control (AGC) circuitry. The output of the AGC amplifier  129  is supplied to AGC rectifier diode  130  and filter capacitors and resistors,  131 ,  132 ,  133  and  134 . This negative AGC voltage is applied, through potentiometer  145 , to a gate of a N-channel MOSFET  135  and thereby reduces the stage gain with increasing AGC voltage. Conversely, with low level AGC voltages (secondary to reduced pre-amplified EKG voltages at the output of integrated circuit  32 ), the output from MOSFET  135  is enhanced. After amplification/inversion by integrated circuit  138 , a nearly constant approximately 2 volt positive output pulse is supplied to capacitor  140  from each electrocardiogram QRS complex (to point D in FIGS. 2 and 3).  
         [0033]    In FIG. 3, Capacitor  140  couples the conditioned and amplified electrocardiogram signal to integrated circuit  38 , which is a Schmitt trigger corresponding to Schmitt trigger ST of FIG. 1. Resistors  36 ,  37 , and  39  set the optimum bias for the trigger&#39;s activation. (When a signal exceeding approximately 1 volt positive, a QRS complex, appears at the input, the output switches from 5 volts to 5 volts.) This output is applied to the trigger circuit  38  and reset inputs of integrated circuit  41 , which is a timer/oscillator generally corresponding to oscillator SO. The free-running period of the oscillator  41  is determined by resistor  42  and capacitor  43 . (Each 5 to −5 volt transition initiates an oscillator cycle, and will begin/reset a new cycle.) Potentiometer  44 , capacitor  45 , and diode  46  transform the square wave oscillator output to a sawtooth waveform and permit the adjustment of its period/slope. The sawtooth waveform is applied simultaneously to a comparator formed by integrated circuits  47  and  48 ,  77  and  78  of FIG. 2, and comparator  64 . Resistors  49  and  50 , and  51  and  52  form voltage dividers to apply reference voltages to the integrated circuit comparators  47 ,  48 . Resistors  49  and  51  are potentiometers whose values are manually set by the stethoscope&#39;s operator to choose the time window to aurally observe. Resistor  53  is the load resistor for the comparators  47 ,  48 . The comparators&#39; output is applied to the input of inverters  54  and  55  to provide comparator buffering/isolation. (A +5 volt/high output of the comparator/buffer represents the on period of the selected time window.)  
         [0034]    The circuitry to prevent adventitious noise is as follows: The sawtooth waveform that was applied to the comparators  47 ,  48  is also applied to the inverting input of comparator  64 . As the down-sweep of the sawtooth reaches 0 volts, the comparator&#39;s output goes high to +5 volts. After inversion by inverter  65 , a negative going pulse is differentiated by operational amplifier  70  to provide a brief positive pulse only when the sawtooth reaches zero. This pulse provides one input to NOR gate  72 . Additionally, the output of comparators  47 ,  48  is applied to the input of differentiator  60 . Differentiator  60  outputs a positive pulse only when the comparators&#39; output drops from +5 volts to zero volts. This pulse is applied to NOR gate  71  (which in conjunction with NOR gate  72 , form a D-latch whose output is applied to inverter  74 . The output of inverter  74 , and the output of inverter  55  are applied to inverter  75 .  
         [0035]    The above series of inverters, differentiators, and NOR gates function in unison to switch off the analog switch (whenever the time window is not manually set to fully open) immediately when comparators  47 ,  48  begin to go negative and do not permit the switch to open until the sawtooth wave has re-initiated its cycle.  
         [0036]    An example of the necessity of the noise suppression circuitry follows: A “time window” from ¼ to ¾ of, for example, a 1 second cardiac cycle is manually selected. As a result, the comparators&#39; output would swing, at ¼ second, from 0 volts to 5 volts and turn on the audio amplifier. At ¾ second, the comparators&#39; output would fall to 0 volts. However, to prevent a momentary re-triggering of a 5 volt output from the comparators (during the down-slope of the sawtooth waveform at the comparators input, a momentary positive pulse is outputted), this falling sawtooth edge generates a momentary positive pulse from differentiator  60  and triggers the D-latch, and through inverter  74 , holds the input to inverter  75  low and keeps the analog switch off. However, to enable a new cardiac cycle to be enabled, comparator  64 , enabled by the onset of a new sawtooth waveform, subsequently generates a brief positive pulse through differentiator  70  to trigger the D-latch to remove the low voltage from inverter  75 . This low signal removal permits control of the analog switch to revert to comparators  47 ,  48  until the above cycle repeats.  
         [0037]    The output of inverter  75  is applied to the input of analog switch  76 . The output (switch) terminals of switch  76 , A and B, are connected to the stethoscope audio amplifier signal path between capacitors  110  and capacitor  111  of FIG. 3 and pass the audio signal when the switch is closed.  
         [0038]    As stated above, integrated circuits  77  and  78  of FIG. 4, also receive the sawtooth wave output. Both circuits are light emitting diode (LED) array drivers, which, in combination, sequentially illuminate a swept array of LEDs,  79  and  80 , to display both EKG “capture” and the time interval through the cardiac cycle. (This permits the precision adjustment of the time window to be selected, and the manual adjustment of period of the sawtooth waveform.) Resistors  81  and  82  are used to select the voltage range for the sweep of the full diode array.  
         [0039]    Also shown in FIG. 4 is the audio amplifier portion of the cardiac stethoscope. Resistor  83  supplies power to electret microphone  84 , which is located behind the diaphragm portion of the chest-piece  85  of the “conventional” stethoscope head.  
         [0040]    Capacitor  86  and resistor  87  provide coupling and low pass filtering at 20 Hertz for the output of the microphone. The signal is applied to the input of operational amplifier  88 . Resistor  89  and resister  90  determine the stage gain.  
         [0041]    Capacitors  91  and  92  and potentiometers  93  and  94 , and limit resistors  95  and  96  comprise a high pass filter which outputs to operational amplifier  97 , connected as a unity gain stage.  
         [0042]    Potentiometers  93  and  94  permit adjustment of the low frequency cutoff from between 20 and 1000 Hertz. This stage outputs to potentiometers  98  and  99 , limit resistors  100  and  101 , and capacitors  102  and  103  which comprise a low pass filter that outputs to unity gain operational amplifier  104 .  
         [0043]    Potentiometers  98  and  99  permit adjustment of the high frequency cutoff of the amplifier from between 200 and 3000 Hertz.  
         [0044]    Amplifier  104  outputs to capacitor  105  and resistor  106 , a 20 Hertz high pass filter. This filter outputs to operational amplifier  107 . Resistor  108  and potentiometer  109  determine the gain of amplifier  107 . Potentiometer  107  is the manually controlled volume control for the composite unit.  
         [0045]    As stated above, the analog switch integrated circuit  76  is connected between capacitor  110  and coupling capacitor  111 . This capacitor outputs to transistor  112 , a power output stage.  
         [0046]    Resistor  113  sets the proper operational bias for the stage. Resistor  114  is a current limiting resistor. Transistor  112  drives transducer  115 . Transducer  115  converts the electrical output of transistor  112  to an acoustic/audio signal, which is directed into conventional stethoscope tubing/earpieces  116 .  
         [0047]    [0047]FIG. 4 also illustrates a dual polarity regulated power supply which is composed of two 9-volt batteries  117  and  118 , a positive 5-volt regulator  119 , a negative 5-volt regulator  120 , and two filter capacitors  121  and  122 , providing −5 and +5 volt supply voltages, a DPST switch and a LED indicator light.  
         [0048]    Although the invention is obviously not limited to the specific implementation described above, typical values for the components shown in FIGS. 2, 3 and  4  are as follows:  
         [0049]    1. patient skin surface electrode/input connector  
         [0050]    2. patient skin surface electrode/input connector  
         [0051]    3. 10K Ohms resistor  
         [0052]    4. 10K Ohms resistor  
         [0053]    5. 1 Meg Ohms resistor  
         [0054]    6. 1 Meg Ohms resistor  
         [0055]    7. 100K Ohms resistor  
         [0056]    8. 18K Ohms resistor  
         [0057]    9. 100K Ohms resistor  
         [0058]    10. ½ LF353 integrated circuit operational amplifier  
         [0059]    11. ½ LF353 integrated circuit operational amplifier  
         [0060]    12. 27K Ohms resistor  
         [0061]    13. 27K Ohms resistor  
         [0062]    14. 220K Ohms resistor  
         [0063]    15. LF356 integrated circuit operational amplifier  
         [0064]    16. 220K Ohms resistor  
         [0065]    17. 220 microfarads electrolytic capacitor  
         [0066]    18. 4.7K Ohms resistor  
         [0067]    19. ¼ MC3403 integrated circuit operational amplifier  
         [0068]    20. 100K Ohms resistor  
         [0069]    21. 330K Ohms resistor  
         [0070]    22. 0.02 microfarad capacitor  
         [0071]    23. 0.068 microfarad capacitor  
         [0072]    24. ¼ MC3403 integrated circuit operational amplifier  
         [0073]    25. 100K Ohms resistor  
         [0074]    26. 330K Ohms resistor  
         [0075]    27. 0.02 microfarad capacitor  
         [0076]    28. 0.068 microfarad capacitor  
         [0077]    29. ¼ MC3403 integrated circuit operational amplifier  
         [0078]    30. 220 microfarads electrolytic capacitor  
         [0079]    31. 4.7K Ohms resistor  
         [0080]    32. ¼ MC3403 integrated circuit operational amplifier  
         [0081]    33. 4.7K Ohms resistor  
         [0082]    34. 100K Ohms potentiometer  
         [0083]    35. 10 microfarads electrolytic capacitor  
         [0084]    36. 2.2K Ohms resistor  
         [0085]    37. 100K Ohms resistor  
         [0086]    38. ⅙ 74LS14N Schmitt trigger  
         [0087]    39. 220 Ohms resistor  
         [0088]    40. 12K Ohms resistor  
         [0089]    41. NE555 Oscillator/Timer integrated circuit  
         [0090]    42. 200K Ohms potentiometer  
         [0091]    43. 10 microfarads capacitor  
         [0092]    44. 10K Ohms potentiometer  
         [0093]    45. 47 microfarads capacitor  
         [0094]    46. 1N34A germanium diode  
         [0095]    47. ¼ LM339 quad comparator  
         [0096]    48. ¼ LM339 quad comparator  
         [0097]    49. 10K Ohms slide potentiometer  
         [0098]    50. 27K Ohms resistor  
         [0099]    51. 10K Ohms slide potentiometer  
         [0100]    52. 27K Ohms resistor  
         [0101]    53. 10K Ohms resistor  
         [0102]    54. ⅙ CD4049 inverter  
         [0103]    55. ⅙ CD4049 inverter  
         [0104]    56. 0.33 microfarad capacitor  
         [0105]    57. 10K Ohms resistor  
         [0106]    58. 10K Ohms resistor  
         [0107]    59. 100K Ohms resistor  
         [0108]    60. ½MC33172 integrated circuit  
         [0109]    61. 12K Ohms resistor  
         [0110]    62. 220K Ohms resistor  
         [0111]    63. 1 Meg Ohms resistor  
         [0112]    64. ¼ LM339 quad comparator  
         [0113]    65. ⅙ CD4049 inverter  
         [0114]    66. 0.33 microfarad capacitor  
         [0115]    67. 10K Ohms resistor  
         [0116]    68. 10K Ohms resistor  
         [0117]    69. 100K Ohms resistor  
         [0118]    70. ½ MC33172 integrated circuit  
         [0119]    71. ¼ CD4001M quad NOR gate  
         [0120]    72. ¼ CD4001M quad NOR gate  
         [0121]    73. 12K Ohms resistor  
         [0122]    74. ⅙ CD4049 inverter  
         [0123]    75. ⅙ CD4049 inverter  
         [0124]    76. DG200ACJ analog switch integrated circuit  
         [0125]    77. LM3914 LED array driver integrated circuit  
         [0126]    78. LM3419 LED array driver integrated circuit  
         [0127]    79. 10 segment LED display  
         [0128]    80. 10 segment LED display  
         [0129]    81. 1500 Ohms resistor  
         [0130]    82. 2700 Ohms resistor  
         [0131]    83. 4.7K Ohms resistor  
         [0132]    84. electret microphone  
         [0133]    85. stethoscope pickup hand-piece  
         [0134]    86. 0.1 microfarad capacitor  
         [0135]    87. 1000 Ohms resistor  
         [0136]    88. ¼ MC3403 integrated circuit operational amplifier  
         [0137]    89. 1000 Ohms resistor  
         [0138]    90. 27K Ohms resistor  
         [0139]    91. 0.1 microfarad capacitor  
         [0140]    92. 0.1 microfarad capacitor  
         [0141]    93. ½ dual 100K Ohms potentiometer  
         [0142]    94. ½ dual 100K Ohms potentiometer  
         [0143]    95. 2.2K Ohms resistor  
         [0144]    96. 2.2K Ohms resistor  
         [0145]    97. ¼ MC3403 integrated circuit operational amplifier  
         [0146]    98. ½ dual 500K Ohms potentiometer  
         [0147]    99. ½ dual 500K Ohms potentiometer  
         [0148]    100. 3000 Ohm resistor  
         [0149]    101. 3000 Ohm resistor  
         [0150]    102. 0.005 microfarad capacitor  
         [0151]    103. 0.01 microfarad capacitor  
         [0152]    104. ¼ MC3403 integrated circuit operational amplifier  
         [0153]    105. 10 microfarads capacitor  
         [0154]    106. 1000 Ohms resistor  
         [0155]    107. ¼ MC3403 integrated circuit operational amplifier  
         [0156]    108. 1000 Ohms resistor  
         [0157]    109. 100K Ohm potentiometer  
         [0158]    110. 47 microfarads electrolytic capacitor  
         [0159]    111. 47 microfarads electrolytic capacitor  
         [0160]    112. 2N4904 transistor  
         [0161]    113. 3.8K Ohms resistor  
         [0162]    114. 100 Ohms resistor  
         [0163]    115. 8 Ohms audio transducer  
         [0164]    116. stethoscope tubing/earpieces  
         [0165]    117. 9 Volt battery  
         [0166]    118. 9 Volt battery  
         [0167]    119. 7805 5 volt positive voltage regulator  
         [0168]    120. 7905 5 volt negative voltage regulator  
         [0169]    121. 1000 microfarads capacitor  
         [0170]    122. 1000 microfarads capacitor  
         [0171]    123. DPST switch  
         [0172]    124. 1000 Ohms resistor  
         [0173]    125. light emitting diode  
         [0174]    126. 3000 Ohms resistor  
         [0175]    127. 4700 Ohms resistor  
         [0176]    128. 10K Ohms potentiometer  
         [0177]    129. ½ LF353 integrated circuit operational amplifier  
         [0178]    130. 1N34A diode  
         [0179]    131. 15K Ohms resistor  
         [0180]    132. 220 microfarads electrolytic capacitor  
         [0181]    133. 15K Ohms resistor  
         [0182]    134. 220 microfarads electrolytic capacitor  
         [0183]    135. ECG221 dual gate MOSFET transistor  
         [0184]    136. 15 Ohms resistor  
         [0185]    137. 1500 Ohms resistor  
         [0186]    138. ½ LF353 integrated circuit operational amplifier  
         [0187]    139. 38K Ohms resistor  
         [0188]    140. 1000 microfarads electrolytic capacitor  
         [0189]    141. 1000 microfarads electrolytic capacitor  
         [0190]    142. 1500 Ohms resistor  
         [0191]    143. 1000 Ohms resistor  
         [0192]    144. 470 microfarads electrolytic capacitor  
         [0193]    145. 100K Ohms potentiometer  
         [0194]    146. 3300 Ohms resistor  
         [0195]    147. Misc: case, printed circuit, wiring, knobs, screws/hardware, solder, etc.  
         [0196]    Although one preferred embodiment has been described above, it will be appreciated that many modifications and variations may be made in this embodiment. For example, the invention can employ LSI (large scale integration) integrated circuits incorporating all of or virtually all of the above components of the device/circuits (most likely using MOSFETs—metal oxide semiconductor field effect transistors—and FETs to minimize power consumption). Further, a LCD (liquid crystal display) can be used in place of LED display. In addition, a real time electrocardiographic display can be incorporated in parallel (simultaneously) with the sweep display on an LCD display. Further, an integrated miniaturized system (a LSI system as above) can be physically in line with stethoscope pickup and earpiece.  
         [0197]    There can also be variations in the mechanism of the sawtooth generation circuit, e.g., a unijunction transistor circuit can be used, including one with second order compensation, and power supply variations, including miniature cell supplies, or single battery supplies, etc.  
         [0198]    In addition, a single IC integrated instrumentation amplifier front end EKG amplifier can be used. Variations of the automatic gain control (a subcomponent IC of the LSI IC for the EKG amplifier) to obviate manual adjustment can be incorporated as can an automatic sweep width control for the sawtooth waveform generator components (to obviate manual adjustment).  
         [0199]    It is, of course, also understood that equivalent semiconductors can be used in place of any or all of those specified in the preferred embodiment (e.g., a CD4066 quad analog switch integrated circuit can be substituted for the DG200ACJ analog switch). Further, a radio-telemetered EKG signal from the examinee to the time and frequency windowed electronic subunit can be employed to obviate/minimize motion artifacts to EKG pickup electrodes. Further, a radio-telemetered stethoscopic head audio transmitted to the time and frequency windowed electronic subunit can be used to obviate wiring inconvenience between the pickup and stethoscopic headphone unit. Further, additional stages of low pass filtering in the EKG amplifier can be provided to further reduce the 60 Hertz noise artifact.  
         [0200]    Finally, while the invention has been described above relative to a preferred embodiment and specific variations and modifications thereof, it is also to be understood that still further variations and modifications may be made without departing from the scope and spirit of the invention.