Abstract:
An apparatus and method for detecting infrasonic cardiac apical impulses of a patient including a sensor disposable in contact with skin of the patient for producing a signal responsive to a motion of the skin at an infrasonic cardiac apical impulse point of the patient. A first circuit coupled to the first sensor for generating at least one audible output in response to the first signal and indicative of the infrasonic cardiac apical impulse. A dampening ring surrounding the sensor for dampening the relative motion of the sensor with respect to movement of the patient.

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical diagnostic instruments, and more particularly, to such instruments for detecting abnormal heart functions. 
     BACKGROUND INFORMATION 
     Patients occasionally develop heart disease, the prompt and timely discovery of which can be determinative of patients&#39; health and survival. Until the 19th century, medical caregivers had to press their ears against patients&#39; chests in order to hear heart sounds. When the stethoscope (“spy of the chest” in Greek) was introduced by René Laennec (1781-1826), it enabled medical caregivers to hear heart sounds with improved ease and clarity. “In search of the perfect stethoscope that hears all heart sounds, and explains them to you.” (Laennec) 
     The ballistic recoiling of the heart produces a vibration when it moves its apex upward, rightward, and against the underside of the chest wall before the ejection of blood. This motion or vibration is typically inaudible and infrasonic, having a sound frequency of less than about 30 Hertz. There are other low frequency, low amplitude vibrations which normally occur during cardiac filling. There are also abnormal cardiac vibrations with sound frequencies as low as about 10 Hertz, but of high amplitude that occur when the heart fills abnormally. The period of cardiac filling is called diastole, and when these abnormal vibrations occur, they indicate diastolic dysfunction of the heart. These abnormal vibrations during diastole are called pathologic gallops. Some gallops are faint and difficult to hear, and some are infrasonic. 
     There are two types of pathologic gallops of primary clinical significance: An S4 type of gallop, which occurs during late diastole; and an S3 type of gallop, which occurs during early diastole. Many gallops are palpable and visible even when they are inaudible. This is because they are of high-energy amplitude despite their low frequencies. Detection of gallops is very important, and can lead to the diagnosis and treatment of such cardiac disorders as hypertrophic heart syndromes, valvular lesions, cardiomyopathies, and congenital heart problems. 
     A visual and palpable assessment of cardiac motion of a patient in the supine position may be made at the left chest wall near the left breast. This location is called the cardiac apical impulse, and for purposes of clarity is also herein referred to as the cardiac apical impulse point. The cardiac apical impulse point is a single area typically less than about 15 millimeters in diameter. The skin motion at this location is normally caused by the recoiling of the heart when it moves its ventricular apex upward, rightward, and against the underside of the chest wall. Presently, medical caregivers may examine the heart motions at the cardiac apical impulse point by placing their fingertips against the skin at this point to enable tactile detection of apical impulses having sufficient amplitude. 
     Over the past 60 years, sophisticated and elaborate laboratory apparatus have been developed to detect and record heart movements, and enable medical caregivers to analyze the data for indications of abnormal heart conditions. The apexcardiogram (“ACG”), for example, which was in popular use until the early 1980&#39;s, was capable of revealing low frequency heart motions by means of electromechanical sensors affixed to a patient&#39;s chest. The ACG signals were recorded on a strip chart recorder for later analysis. An electrocardiogram (“EKG”) and a separate phonocardiogram were required to be performed contemporaneous with the ACG in order to provide correlation between the low frequency heart motions and the additional heart signals. The three charts were then correlated, as by technicians, for later analysis by caregivers. Although this method was very useful for detecting heart irregularities in suspected cases, the time delay incurred by a patient between seeing a physician for referral to an ACG laboratory, testing in the laboratory by technicians, correlation of strip chart results, and analysis and diagnosis by at least one physician, generally hindered prompt and effective treatment in time-critical cases. In addition, the large expense for this labor-intensive procedure may have precluded its use in many instances. 
     By the mid-1980&#39;s, the ACG had been generally displaced by the echocardiogram. The echocardiogram uses ultrasonic waves to monitor heart function and provides more detail than the ACG. Unfortunately, the echocardiogram suffers from some of the same drawbacks as the ACG, including the requirement for special laboratory testing and associated expense. Like the ACG, the echocardiogram also fails to produce recognizable sounds indicative of the infrasonic heart motions, and therefore fails to disclose a method for their discovery. 
     Various other prior art systems are also directed toward monitoring human heart function. For example, U.S. Pat. No. 5,218,969 to Bredesen et al. (“the &#39;969 patent”) depicts an electronically enhanced stethoscope for detecting heart sounds. However, the &#39;969 patent teaches filtering out sounds below 50 Hz (see FIG. 3F). Since human hearing is generally recognized to extend to at least as low as 30 Hz, the stethoscope of the &#39;969 patent is not capable of detecting heart vibrations of frequency below the range of human hearing, even if it may amplify low amplitude sounds which are above 50 Hz. Accordingly, the electronic stethoscope of the &#39;969 patent does not detect infrasonic cardiac apical impulses, and in fact is incapable of detecting any phenomena emitting a frequency below 50 Hz. 
     U.S. Pat. No. 5,178,151 to Sackner (“the &#39;151 patent”) shows another system for detection of heart irregularities. The &#39;151 patent shows placement of a plurality of motion transducers about the thoracic region of a patient&#39;s chest wall. Blood vessel volume, blood pressure waveforms, and other thoracic motions including respiratory and cardiac apical motions are measured as conglomerate signals that must be further analyzed to determine the presence of heart irregularities. Due in part to its bulk, complexity, cost, and requirement for further analysis, this system suffers from design constraints that generally preclude its inclusion in a general caregiver&#39;s office. The apparatus of the &#39;151 patent further lacks provision for transmitting the acoustic heart waveform data typically relied on during a routine physical examination. 
     The basic acoustic stethoscope, whether electronically amplified, filtered or not, can only be used to hear what Rene Laennec heard with his original wooden device. Only a small percentage of the vibrations of the heart are actually detected by an acoustic stethoscope. These audible vibrations range between about 40 Hertz to 500 Hertz and about 0.002 to 0.5 dynes/cm 2  (amplitude). The remaining vibrations are inaudible because of the typical thresholds of human hearing. Infrasonic vibrations of sufficient amplitude have heretofore only been detectable with bulky, complex, and costly apparatus requiring labor intensive analysis. Heart gallops rest near the division of audible and infrasonic vibrations. Heart gallops have been called the heart&#39;s “cries for help.” Detection of these vibrations is important in diagnosing cardiac pathology and is why palpation of the cardiac apical impulse is an extremely important, yet often neglected, part of the cardiac exam. 
     All in all, the above-described prior art fails to recognize the utility of detecting infrasonic heart motions and producing audible outputs that are indicative of those motions. Such prior art also fails to put infrasonic heart motion data in context with traditional acoustic heart data. It is therefore an object of the present invention to overcome the above-described significant drawbacks and disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a cardiac impulse detector for use in routine cardiac examinations, which employs a sensor capable of detecting infrasonic cardiac apical impulses of a patient. The detector produces audible and optionally visual outputs indicative of those impulses for contemporaneous consideration by a medical caregiver when the sensor is placed in contact with the patient&#39;s skin surface at the cardiac apical impulse point. 
     In an embodiment of the present invention, a sensing protrusion or button is placed in contact with the skin surface of the patient at the patient&#39;s cardiac apical impulse point. The cardiac apical impulse point is located near the left breast. The sensing button is mounted to a piezoelectric sensor, and causes the sensor to respond to the infrasonic heart motions or impulses at the cardiac apical impulse point of the patient. A circuit is electronically connected to the piezoelectric sensor and generates audible and visual outputs indicative of the heart motions. The piezoelectric sensor is housed in one end of an hourglass shaped housing, which provides the caregiver with a convenient grip for holding the device against the cardiac apical impulse point. 
     This embodiment of the detector further employs a traditional acoustic diaphragm mounted at the opposite end of the housing relative to the piezoelectric sensor. The acoustic diaphragm can transmit acoustic heart sounds to an earpiece worn by the caregiver when the acoustic end of the sensor housing is placed in contact with the patient&#39;s chest, and a selection manifold has been rotated 180 degrees in order to transmit the traditional acoustic sounds instead of the signals indicative of infrasonic heart motions. The sounds may be electronically amplified and/or filtered. This embodiment has the distinct advantage of placing the audible signal indicative of an infrasonic cardiac impulse in temporal context with the traditional acoustic cardiac sounds familiar to the caregiver. 
     In accordance with another aspect of the present invention, an apparatus is provided for detecting infrasonic cardiac apical impulses of a patient. The apparatus comprises a flexible substrate including (i) a skin-contacting surface located on one side of the substrate that is disposable in contact with a skin surface region of a patient defining an infrasonic cardiac apical impulse point, and is movable with the contacted skin surface region in response to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point; and (ii) a reflective surface located on an opposite side of the substrate relative to the skin-contacting surface and movable with the skin-contacting surface in response to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point. A light source, such as a laser, is spaced apart from and faces the reflective surface of the substrate. The light source transmits light onto the reflective surface, and the reflective surface reflects light transmitted thereon by the light source. An optical sensor is spaced apart from and faces the reflective surface. The optical sensor receives reflected light directed by the reflective surface and generates a first signal indicative of movement of the reflective and skin-contacting surfaces and corresponding to a subaudible motion of the contacted skin at the infrasonic cardiac apical impulse point. An electric circuit is coupled to the optical sensor for generating (i) an audible output and/or (ii) a visual output, in response to the first signal and indicative of an infrasonic cardiac apical impulse. 
     In accordance with another aspect, the present invention is directed to a method for detecting infrasonic cardiac apical impulses of a patient, comprising the following steps: 
     (i) providing a flexible substrate including a skin-contacting surface located on one side of the substrate and a reflective surface located on an opposite side of the flexible substrate relative to the skin-contacting surface; 
     (ii) positioning the skin-contacting surface of the flexible substrate in contact with a skin surface region of the patient defining an infrasonic cardiac apical impulse point on the patient&#39;s chest; 
     (iii) allowing movement of the skin-contacting and reflective surfaces of the flexible substrate with movement of the skin surface region of the patient in response to a subaudible motion of the skin at the infrasonic cardiac apical impulse point; 
     (iv) transmitting light from a light source onto the reflective surface of the flexible substrate positioned on the skin surface region of the patient defining the infrasonic cardiac apical impulse point; 
     (v) reflecting transmitted light from the light source with the reflective surface of the flexible substrate positioned on the skin surface region of the patient defining the infrasonic cardiac apical impulse point; 
     (vi) receiving with an optical sensor reflected light directed by the reflective surface, and generating a first signal indicative of movement of the reflective and skin-contacting surfaces and corresponding to a subaudible motion of the skin at the infrasonic cardiac apical impulse point; 
     (vii) processing the first signal electronically; and 
     (viii) generating (i) an audible output and/or (ii) a visual output, indicative of an infrasonic cardiac apical impulse. 
     A primary advantage of the present invention is that it may provide an efficient way to screen patients for abnormal infrasonic vibrations or pathological gallops during routine physical examinations, a clearly desirable improvement over current procedure which requires elaborate set-up of bulky apparatus. Other objects and advantages of the present invention will become apparent in view of the following Detailed Description of the Preferred Embodiments and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a somewhat schematic, elevational view of a first embodiment of a cardiac impulse detector embodying the present invention. 
     FIG. 2 is a cross-sectional view of the cardiac impulse detector taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is an exploded, partial, somewhat schematic, cross-sectional view of the cardiac impulse detector of FIGS. 1 and 2. 
     FIG. 4 is a schematic illustration of electronic circuitry of the cardiac impulse detector of FIGS. 1,  2  and  3 , for driving a speaker and Light Emitting Diode in response to a sensed heart motion at the cardiac apical impulse point. 
     FIG. 5 is a somewhat schematic, elevational view of a second embodiment of a cardiac impulse detector embodying the present invention. 
     FIG. 6 is a cross-sectional view of the cardiac impulse detector taken along line  6 — 6  of FIG.  5 . 
     FIG. 7 is a schematic illustration of electronic circuitry of the cardiac impulse detector of FIGS. 5 and 6, for driving a speaker in response to a sensed heart motion at the cardiac apical impulse point. 
     FIG. 8 is a cross-sectional view of a third embodiment of a cardiac impulse detector embodying the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a first embodiment of the cardiac impulse detector of the present invention is indicated generally by the reference numeral  10 . The cardiac impulse detector  10  comprises an earpiece  11  connected to a sensor assembly  12  via acoustic tubing  13 . The sensor assembly  12  comprises a diaphragm  14  including a piezoelectric elementl 6  superimposed over a substrate  18 , wherein the diaphragm is mounted around its circumference to a housing  20 . A sensing protuberance  22  is mounted to the piezoelectric element  16 . A dampening member  30  is mounted to the housing  20  at one end, and surrounds the sensing protuberance  22  without contact. The housing  20  is hourglass shaped in order to transmit acoustic pressure waves with minimal attenuation and distortion, and to provide a convenient grip for placement of a caregiver&#39;s hand. 
     Turning to FIGS. 2 and 3, the sensing protuberance  22  is mounted to the piezoelectric element  16  at about its center. In this embodiment of the present invention, the sensing protuberance  22  is made of nylon and is rounded and convex, allowing it to nest longitudinally in the intercostal space at a patient&#39;s cardiac apical impulse point, thus coming into contact with the skin tissue over the cardiac apex. As the ventricular apex of the heart strikes the internal surface of the rib cage, it generates an impulse, which, coupled through the tissue, strikes the sensing protuberance  22 . As may be recognized by those skilled in the pertinent art based on the teachings herein, the sensing protuberance  22  may take any of numerous different shapes for performing the functions of the exemplary protuberance, such as a globular, ovate, or other substantially smooth shape. Likewise, the sensing protuberance  22  may be made of any of numerous different materials for performing the functions of the protuberance described herein, such as polyurethane or thermoplastic rubber. 
     When the sensing protuberance  22  is struck, it deflects the diaphragm  14 , and thus the piezoelectric element  16 . The piezoelectric element  16  is a natural mechanical differentiator and a transducer of mechanical movement into electrical signals. When deflected, it generates a momentary charge. It is not a sustained voltage potential but a voltage spike that decays rapidly, indicating proportional changes in forces applied to the diaphragm  14 . This characteristic is advantageous for this application in order to detect low frequency or infrasonic cardiac movements. When the cardiac apex strikes the sensing protuberance  22 , the momentary charge is generated by the piezoelectric element  16 . An electronic circuit  24  is connected to the piezoelectric element  16 , and electronically detects the momentary charge indicative of the heart motion at the cardiac apical impulse point. An audio speaker  26  and a light emitting diode (“LED”)  28  are connected to the electronic circuit  24 , and generate outputs corresponding to the detected cardiac apical motion. These indications provide the caregiver the means to audibly and visibly observe and correlate normal and abnormal infrasonic cardiac apical impulses. As may be recognized by those skilled in the pertinent art based on the teachings herein, the speaker  26  may be supplemented or replaced by any of numerous different audible transducers for performing the functions of the speaker described herein, such as a piezoelectric buzzer, or other audible indicator. Likewise, the LED  28  may be supplemented or replaced by any of numerous different visible indicators for performing the functions of the LED described herein, such as an electrical light bulb, liquid crystal display, graphical monitor or computational device. 
     The diaphragm&#39;s substrate  18  is made of MYLAR® film, mounted at its outer diameter to the housing  20 . As may be recognized by those skilled in the pertinent art based on the teachings herein, the MYLAR® film may be replaced with any of a number of suitable materials for performing the functions of the substrate described herein, such as spring steel or other resilient material. The diaphragm  14  is preferably taut so that it is mechanically biased, which will, in turn, lead to enhanced sensitivity when the protuberance  22  is placed on a patient. 
     The location of the dampening member  30  around the outer diameter of the diaphragm  14  provides a mechanical stabilizing and decoupling effect when the cardiac impulse detector  10  is placed on a patient&#39;s skin. In this embodiment, the dampening member  30  is in the form of a ring and made of foam rubber. As may be recognized by those skilled in the pertinent art based on the teachings herein, the dampening member  30  may comprise any of numerous different materials or mechanisms which now or later become known for performing the functions of the dampening member described herein, such as foam, rubber, soft polyurethane, or a hydraulic fluid damper. As also may be recognized by those skilled in the pertinent art based on the teachings herein, the dampening member  30  may take any of numerous different shapes for performing the functions of the dampening member described herein, such as oval, elongated, or rectangular. This configuration for interfacing the diaphragm  14  to the cardiac apex promotes improved signal acquisition and reduced secondary motion from the caregiver&#39;s hand or inadvertent patient movements. 
     The cardiac impulse detector  10  further comprises a battery  32  mounted to the housing  20 , and electrically connected to a momentary power switch  34 , which, in turn, is electrically connected to the electronic circuit  24  to supply power for the circuit and for the indicators  26  and  28 . The battery  32  is to be replaced if the indicators do not activate when the sensing protuberance  22  is intentionally touched. In this embodiment of the present invention, the detector  10  is only active when the momentary power switch  34  is depressed, typically by operation of a caregiver&#39;s finger, which is intended to be done while the detector  10  is in place on a patient. When the finger moves from the switch  34 , the power goes off, conserving energy in the battery  32 . 
     The cardiac impulse detector  10  further comprises a traditional acoustic diaphragm  38  mounted to the opposite side of the housing  20  relative to the diaphragm  14 . In operation, the sensor housing  20  is preferably placed on a patient&#39;s chest with the acoustic diaphragm  38  in unobstructed contact with the patient&#39;s chest in order to obtain the least amount of acoustic attenuation. The acoustic diaphragm responds to local sound-pressure waves in the tissue medium against its outer surface by reproducing the sound-pressure waves in the gaseous medium against its inner surface. Thereafter, the waves are propagated in substantially unattenuated form towards the closest pressure equilibrium point, normally an earpiece. The acoustic diaphragm effectively amplifies incident sounds by receiving sound pressure over a larger area than that of the equilibrium point or earpiece. As may be recognized by those skilled in the pertinent art based on the teachings herein, the traditional acoustic diaphragm  38  may be augmented or replaced with any of numerous different sensors for performing the functions of the exemplary acoustic diaphragm, such as an electronic microphone or similar device for sensing acoustic heart sounds. For example, a piezoelectric microphone may be employed to sense acoustic heart sounds, while an electronic amplifier and speaker transduce the electronic signal back into audible sound. 
     A selection manifold  36  is acoustically coupled to the speaker  26  and the acoustic diaphragm  38 . The selection manifold enables alternate acoustic connection of the speaker  26  and the diaphragm  38 . As shown in FIG. 1, the earpiece  11  is connected through the acoustic tubing  13  to the selection manifold  36  to receive sound from at least one of the speaker  26  and the acoustic diaphragm  38 . A caregiver may rotate the selection manifold  36  one half turn (180°) to create a path for one sound source and block the other, thereby blocking loss of the desired sound-pressure across the unused diaphragm. The manifold  36  is turned in the opposite direction to switch between the sound sources  38  and  26 . 
     Turning now to FIG. 4, the electronic circuit  24  employs a front-end charge amplifier sub-circuit  40  of typically high gain to amplify the voltage signal generated by the piezoelectric element  16 . A first differential output of the piezoelectric element  16  is connected through a resistor  62  to an inverting input of an operational amplifier (“op-amp”)  58 . The inverting input of the op-amp  58  is also connected to a negative feedback path comprising a capacitor  42  and a resistor  60 , connected in parallel between the output of the op-amp  58  and its inverting input. The non-inverting input of the op-amp  58  is connected to a reference potential V REF , prescribing the gain. A second differential output of the piezoelectric element  16  is connected through a resistor  63  to an inverting input of an op-amp  59 . The inverting input of the op-amp  59  is also connected to a negative feedback path comprising a capacitor  43  and a resistor  61 , connected in parallel between the output of the op-amp  59  and its inverting input. The non-inverting input of the op-amp  59  is connected to the reference potential V REF , prescribing the gain. The capacitors  42  and  43  in the feedback paths enhance the amplification of the voltage potential generated by the piezoelectric element  16 . A secondary amplification stage is implemented by an op-amp  64 , which receives at its non-inverting input the voltage from the op-amp  59  divided across a resistor  65 , with a resistor  66  completing the path to ground potential. The op-amp  64  receives at its inverting input the sum of the output of the op-amp  58  received across a resistor  68 , and the direct feedback signal received across a resistor  70 . 
     After the amplification stage, a comparator sub-circuit  45  generates a voltage pulse of variable duration corresponding to the detected cardiac apical impulse. The output from the op-amp  64  is connected across a capacitor  44  to the inverting input of a variable threshold comparator  52 . The capacitor  44  functions as an AC coupled filter. The inverting input of the comparator  52  is also connected to the anode of a diode  48 . Each cardiac apical impulse charges a threshold capacitor  46  through the diode  48 . The cathode of the diode  48  is connected to the non-inverting input of the comparator  52 . The capacitor  46  is connected to ground in parallel with a resistor  50 , which sets a typically slow time constant. The resistor  50  drains charge from the threshold capacitor  46 , tending to keep its voltage within the operating range of the comparator  52 . The diode  48  creates a voltage difference between the two inputs to the comparator  52  by allowing current to pass from the inverting input towards the non-inverting input, thus incurring a typical voltage drop. The cathode of the diode  48  is connected to the parallel combination of the capacitor  46  and the resistor  50  to ground potential, as well as to the non-inverting input of the comparator  52 . When the input signal from the capacitor  44  is below the voltage level of the threshold capacitor  46 , which occurs between apical impulses, the output of the comparator  52  relative to ground potential is about one half of battery voltage or V+. When there is a cardiac apical impulse, the voltage level of the input signal from the capacitor  44  rises above the voltage level of threshold capacitor  46 , switching the output to about negative one half of battery voltage or V−, thus creating a negative voltage pulse. The initial pulse-width or duration will be the width of the pulse generated by the piezoelectric diaphragm  16 . 
     Typically, the pulse produced by the comparator  52  lacks sufficient duration to activate the speaker  26  or other audible indicator, or the LED  28  or other visual indicator. An output driver sub-circuit  56  utilizes a one-shot integrated circuit (“one-shot”)  54  that is triggered by the pulse from comparator  52  to generate a single pulse of substantially constant duration. The duration of the generated pulse is independent of the duration of the incoming pulse from the comparator  52 . The duration of the pulse generated by the one-shot  54  can be varied in order to optimize the outputs of the indicators  26  and  28 , and to minimize the current required from the battery  32  of FIGS. 2 and 3. The output of the one-shot  54  is connected to a resistor  72 , which, in turn, is connected to the base of an NPN BJT transistor  74 . An emitter of the transistor  74  is connected to ground potential, and a collector of the transistor  74  is connected to the speaker  26 , which, in turn, is connected to V+. Consequently, the transistor  74  drives the speaker  26  in response to the cardiac apical impulse sensed by the piezoelectric element  16 . As may be recognized by those skilled in the pertinent art based on the teachings herein, the exemplary NPN BJT transistor  74  may be replaced with any of numerous different switching devices for performing the functions of the exemplary transistor, such as an FET or other suitable switching device for driving the speaker  26 . 
     The output of the one-shot  54  is also connected to a resistor  76 , which, in turn, is connected to the base of a transistor  78 . An emitter of the transistor  78  is connected to ground potential, and a collector of the transistor  78  is connected to LED  28 , which, in turn, is connected to V+ through a resistor  80 . As may be recognized by those skilled in the pertinent art based on the teachings herein, the exemplary NPN BJT transistor  78  may be replaced with any of numerous different switching devices for performing the functions of the exemplary transistor, such as an FET or other suitable switching device for driving the LED  28 . 
     The LED  28  can be seen by the caregiver as the cardiac impulse detector is held in place on a patient. The audible signal, generated by the speaker  26 , is connected through the tubing  13  of FIG. 1 to the earpiece  11  and can be heard by the caregiver as the cardiac impulse detector is held in place on a patient. 
     In operation, the sensor assembly  12  of the cardiac impulse detector  10  is placed on the cardiac apical impulse point of a patient, with the sensing protuberance  22  contacting the patient&#39;s skin surface at the cardiac apical impulse point. A cardiac apical impulse induces motion of the sensing protuberance  22 , which in turn causes motion of the piezoelectric element  16 . The circuit  24  of FIG. 2 processes the signal from the piezoelectric element  16 , and drives the speaker  26  and the LED  28  in response to the cardiac apical impulse. When a single gallop is present, the speaker will sound twice per heartbeat in a repeating series, and the LED will correspondingly flash twice in a repeating series. At a typical resting pulse rate of about 60 heartbeats per minute, the period between the two sounds indicative of the gallop is noticeably shorter than the period between successive heartbeats. If, on the other hand, the cardiac apical impulse is normal, then the speaker and LED will signal just once in a repeating series, at a rate equal to the pulse rate and will be timed with the upstroke of a peripheral pulse. Abnormal cardiac apical impulses will cause a repeating series of indications representative of the actual number of local peaks in the cardiac apical impulse waveform, where a single gallop waveform has two such peaks, and two gallops have three peaks. The housing  20  may be positioned adjacent to a patient&#39;s chest surface so that the acoustic diaphragm  38  picks up acoustic cardiac sounds and transmits them to the selection manifold  36 . The selection manifold  36  may be rotated to selectively transmit the sound generated by at least one of the speaker  26  and the acoustic diaphragm  38  by rotation of the manifold. The earpiece  11  receives the acoustic signal transmitted by the selection manifold. As may be recognized by those skilled in the pertinent art based on the teachings herein, an electronic amplifier or similar device which is currently or later becomes known for performing the functions of an amplifier may be connected to the earpiece to enhance the quality of the sound received by the caregiver. 
     In FIGS. 5 through 7, a second embodiment of the cardiac impulse detector of the present invention is indicated generally by the reference numeral  110 . The cardiac impulse detector  110  is substantially similar to the cardiac impulse detector  10  described above, and therefore like reference numerals preceded by the numeral  1  are used to indicate like elements. The cardiac impulse detector  110  of FIG. 5 differs from that of FIG. 1 primarily in that the sensor assembly  112  utilizes a laser diode and compatible sensing scheme in lieu of the piezoelectric sensing scheme of the sensor assembly  12 . The application and overall operation of the cardiac impulse detector  110  is substantially similar to that of the cardiac impulse detector  10 . As shown in FIG. 5, the cardiac impulse detector  110  comprises an earpiece  111  connected to a sensor assembly  112  via acoustic tubing  113 . The sensor assembly  112  comprises a flexible diaphragm  114  mounted about its circumference to a housing  120 . An electrical power switch  134  is mounted to the housing  120  for activating the cardiac impulse detector. An audio amplifier  115  is connected to the tubing  113 , and is electrically connected to the power switch  134 , for enhancing the quality of the audio signal. 
     Turning to FIG. 6, the diaphragm  114  comprises a resilient layer  116  and a reflective layer or structure  118  superimposed over the resilient layer. In this embodiment of the present invention, the reflective layer  118  is made of any reflective material sold under the trademark REFLEXITE®. As may be recognized by those skilled in the pertinent art based on the teachings herein, the reflective layer  118  may be made of various other materials having comparably high coefficients of reflectivity, which are currently or later become known for performing the functions of the exemplary reflective layer or structure. A laser diode support  119  is mounted to an inner surface of the housing  120 , and projects outwardly towards the diaphragm. A laser diode  117  is mounted to the free end of the support  119 , and emits a beam of laser light towards the center of the reflective layer  118 . A battery  133  is mounted to the housing  120 , and is electrically connected to the laser diode  117  via a power switch  134  (FIG. 7) for supplying power to the diode. As may be recognized by those skilled in the pertinent art based on the teachings herein, the power switch  134  may comprise a single-position double-throw (SPDT) switch for fulfilling the function of the power switch  134 . Phototransistors  123  are mounted to the laser support  119 . The phototransistors  123  receive the reflected laser light directed by the reflective layer  118 , and generate outputs indicative of the instantaneous position of the diaphragm  114  that are proportional to the infrasonic movements of the cardiac apical impulse. 
     As may be recognized by those skilled in the pertinent art based on the teachings herein, the face of the reflective layer  118  may be specially configured for directing a high percentage of the incident photons directly towards the phototransistors  123 , such as, for example, by having a slightly convex shape, one or more aspheric or condensing lenses, a laser splitter mounted thereon, and/or like features for better directing the reflected light towards the phototransistors. An electronic circuit  124  is mounted to the housing  120 . The electronic circuit  124  receives the outputs from the phototransistors  123 , and generates signals indicative of the movement of the diaphragm  114 . A speaker  126  is mounted to the housing and produces audible outputs corresponding to the signals generated and amplified by the circuit  124 , and indicative of the movement of the diaphragm  114 . The sensor assembly  112  further comprises an acoustic diaphragm  138  mounted to the housing  120  at the end opposite that of the diaphragm  114 . A selection manifold  136  is also mounted to the housing  120 , and may be acoustically coupled to either the acoustic diaphragm  138  or the speaker  126  by rotating the manifold 180 degrees relative to the housing  120 . 
     Turning now to FIG. 7, the electronic circuit  124  is illustrated in further detail. The phototransistors  123  are connected in parallel, emitters to emitters and collectors to collectors, so that the reception of laser light at any one or more of their respective gates will generate a signal to excite the circuit. The collectors are connected to a resistor  181 , which, in turn, is connected to the positive voltage potential (“V BAT ”) terminal of a battery  132 . The negative terminal of the battery  132  is connected to ground potential. The collectors are also connected to a capacitor  182 , which is then connected to a resistor  183 . The resistor  183  is connected to an inverting input of an op-amp  184 . An output of the op-amp  184  is connected to a feedback resistor  185 , which is then connected back to the inverting input of the op-amp. The non-inverting input of the op-amp  184  is connected to a voltage drop resistor  186 , which is connected in turn to V BAT . The non-inverting input of the op-amp is also connected to a parallel combination of a capacitor  187  and a resistor  188 , which are then connected to ground potential. The op-amp  184  functions as an amplifier for the signal generated by the phototransistors  123 , which, in turn, is indicative of a cardiac motion or impulse. The output of the op-amp  184  is further connected to a capacitor  189 . The capacitor  189  is connected, in turn, to a potentiometer  190 . The fixed output of the potentiometer  190  is connected through a capacitor  191  to V BAT . The fixed output terminal of the potentiometer  190  is further connected to an inverting input of a comparator  192 . The variable output terminal of the potentiometer  190  is connected to a resistor  193 , which is then connected to a non-inverting input of the comparator  192 . The adjustment of the potentiometer  190  affects the duration of the pulse generated by the comparator  192 . The output of the comparator  192  is connected to a capacitor  194 , which is ultimately connected to a first terminal of the speaker  126 . A second terminal of the speaker  126  is connected to ground potential. Thus, the speaker  126  is activated for each rise in amplitude of a cardiac apical impulse waveform detected by the phototransistors  123 . 
     In operation, the sensor assembly  112  of the cardiac impulse detector  110  is placed on the cardiac apical impulse of a patient, with the resilient layer  116  contacting the patient&#39;s chest surface at the cardiac apical impulse. A cardiac apical impulse induces motion of the resilient layer  116 , which in turn causes motion of the diaphragm  114  and the reflective layer  118 . The laser diode  117  emits laser light towards the reflective layer  118 . The light is reflected by the reflective layer  118 , and received by the phototransistors  123 . The circuit  124  incorporates the phototransistors in an electronic motion detection scheme as described above, and drives the speaker  126  corresponding to motions of the resilient layer  116 , which is hence keenly indicative of the cardiac apical motion. 
     The cardiac impulse detector  110  is capable of detecting and audibly representing the infrasonic vibrations of the cardiac apical impulse. There are three repetitive major vibrations detected by this device during a regular heart rhythm. 
     The first of these vibrations occurs at the beginning of the left ventricular (“LV”) recoil and causes the detector  110  to produce a first audible signal through the speaker  126  representing the beginning of LV recoil. The second of these vibrations occurs at the beginning of LV ejection and causes the detector  110  to produce a second audible signal through the speaker  126  representing the beginning of LV ejection, and the third of these vibrations occurs at the beginning of LV filling and causes the detector  110  to produce a third audible signal through the speaker  126  representing the beginning of LV filling. The first audible signal occurs in close timing to the normal first heart sound and the counted pulse, and the second audible signal occurs in close timing to the normal second heart sound. The third audible signal occurs after the second heart sound. These three audible signals represent directional change of the cardiac apical impulse motion. 
     These three audible signals are easily recognized and learned by a caregiver. Additional audible signals, which represent abnormal vibrations that are detected during ventricular filling, would thus represent gallops and indicate cardiac pathology. 
     S3 and S4 types of gallops are detectable using the cardiac impulse detector  110 . An extra vibration detected and audibly indicated by the speaker  126 , preceding the first vibration, represents an S4 gallop. An extra vibration detected and audibly indicated by the speaker  126  soon after the third vibration represents an S3 gallop. As may be recognized by those skilled in the pertinent art based on the teachings herein, these detected vibrations and associated output signals could also be indicated visually by means of an LED, and/or displayed graphically using analog or digital processing electronically interfaced to a charge-coupled device or LCD screen. The analog or digital processing also affords electronic storage, playback, compression and analysis of output signals indicative of normal and abnormal vibrations of the cardiac apical impulse. 
     As may also be recognized by those skilled in the pertinent art based on the teachings herein, numerous different processing circuits may be added or substituted for the electronic circuit  124  disclosed herein, in order to produce various signals indicative of particular types of gallops and other abnormal cardiac apical impulses. In addition, as may be recognized by those skilled in the pertinent art based on the teachings herein, when signals indicative of both the infrasonic impulses and the acoustic heart sounds are made present in electronic form, the electronic circuit may utilize the signals indicative of acoustic sounds to supplement the qualification, analysis, and/or categorization of gallops and other abnormal cardiac apical impulses. 
     In FIG. 8, a third embodiment of the cardiac impulse detector sensor assembly of the present invention is indicated generally by the reference numeral  212 . The cardiac impulse detector sensor assembly  212  is substantially similar to the cardiac impulse detector sensor assembly  112  described above, and therefore like reference numerals preceded by the numeral  2  are used to indicate like elements. The cardiac impulse detector sensor assembly  212  of FIG. 8 differs from that of FIG. 6 primarily in that the sensor assembly  212  utilizes a convex reflector and convex collecting lenses with a compatible sensing scheme in lieu of the laser reflector of FIG.  6 . The application and overall operation of the cardiac impulse detector sensor assembly  212  is substantially similar to that of the cardiac impulse detector sensor assembly  112 . 
     As shown in FIG. 8, the cardiac impulse detector sensor assembly  212  comprises a flexible diaphragm  214  mounted about its circumference to a housing  220 . An electrical power switch  234  is mounted to the housing  220  for activating the cardiac impulse detector. An audio amplifier  215  is connected to the tubing  213 , and is electrically connected to the power switch  234 , for enhancing the quality of the audio signal. 
     The diaphragm  214  is connected on its inside surface to a convex reflective structure  218 . In this embodiment of the present invention, the reflective structure  218  is coated on its outer surface with any reflective material, such as that sold under the trademark REFLEXITE®. As may be recognized by those skilled in the pertinent art based on the teachings herein, the reflective structure  218  may comprise various other materials having comparably high coefficients of reflectivity, which are currently or later become known for performing the functions of the exemplary reflective surface of the structure. A laser diode support  219  is mounted to an inner surface of the housing  220 , and projects outwardly towards the diaphragm  214 . A laser diode  217  is mounted to the free end of the support  219 , and emits a beam of laser light towards the center of the reflective structure  218 . A battery  233  is mounted to the housing  220 , and is electrically connected to the laser diode  217  via a power switch  234  for supplying power to the diode. Condensing lenses  221  are mounted to an inner wall of the housing  220 , and are optically coupled to phototransistors  223 , which are mounted to the laser support  219 . The phototransistors  223  receive the reflected laser light through the condensing lenses  221  that is directed by the reflective structure  218 , and generate outputs indicative of the instantaneous position of the diaphragm  214  that are proportional to the infrasonic movements of the cardiac apical impulse. 
     An electronic circuit  224  is mounted to the housing  220 . The electronic circuit  224  receives the outputs from the phototransistors  223 , and generates signals indicative of the movement of the diaphragm  214 . The electronic circuit  224  is substantially similar to the electronic circuit  124 , described above. 
     In operation, the sensor assembly  212  of the cardiac impulse detector  210  is placed on the cardiac apical impulse of a patient, with the flexible diaphragm  214  contacting the patient&#39;s chest surface at the cardiac apical impulse. A cardiac apical impulse induces motion of the diaphragm  214  and the reflective structure  218 . The laser diode  217  emits laser light towards the reflective structure  218 . The light is reflected by the reflective structure  218 , condensed by the condensing lenses  221 , and received by the phototransistors  223 . The circuit  224  incorporates the phototransistors in an electronic motion detection scheme as described above, and drives the speaker  226  corresponding to motions of the flexible diaphragm  214 , which is keenly indicative of the cardiac apical motion. 
     The cardiac impulse detector  210  detects and audibly represents the infrasonic vibrations of the cardiac apical impulse. There are three representative major signals detected by this device during a regular heart rhythm. The first audible signal produced by the detector through the speaker  226  represents the beginning of left ventricular recoil, the second audible signal produced by the detector represents the beginning of left ventricular ejection, and the third audible signal produced represents the beginning of left ventricular filling. These three audible signals are easily learned by a caregiver. Additional sounds produced by the detector, which represent abnormal vibrations detected during ventricular filling, would thus represent gallops and indicate cardiac pathology. As may be recognized by those skilled in the pertinent art based on the teachings herein, these signals may be displayed graphically as well as audibly, such as, for example, by using analog or digital processing, a charge coupled device and a LCD output screen. This embodiment also offers the advantages of electronic storage, playback, compression and analysis of normal and abnormal signals. 
     The cardiac impulse detector  210  further detects S3 and S4 gallops. When a patient presents with an S3 gallop, the speaker  226  will produce a sound immediately following the third sound. When a patient presents with an S4 gallop, the speaker  226  will produce a sound immediately preceding the first sound. 
     As may be recognized by those skilled in the pertinent art based on the teachings herein, numerous different processing circuits may be added or substituted for the electronic circuit  224  disclosed herein, in order to produce various signals indicative of particular types of gallops and other abnormal cardiac apical impulses. In addition, as may be recognized by those skilled in the pertinent art based on the teachings herein, when signals indicative of both the infrasonic impulses and the acoustic heart sounds are made present in electronic form, the electronic circuit may utilize the signals indicative of acoustic sounds to supplement the qualification, analysis, and/or categorization of gallops and other abnormal cardiac apical impulses. 
     One advantage of the above-described embodiments of the present invention is that an audible signal indicative of an infrasonic cardiac apical impulse may be generated for contemporaneous diagnosis by a medical caregiver. 
     Another advantage of the above-described embodiments of the present invention is that an audible signal indicative of an S3 or S4 gallop may be generated during a brief physical examination of a patient. 
     A further advantage of the above-described embodiments of the present invention is that an audible signal indicative of an infrasonic cardiac apical impulse may be supplied in context with traditional acoustic cardiac sounds to promote efficient examination and diagnosis of a patient. 
     An additional advantage of the above-described embodiments of the present invention is that an audible signal indicative of an infrasonic cardiac apical impulse may be generated in a medical school curriculum to promote enhanced understanding of the clinical manifestations of various heart diseases. 
     As may be recognized by those skilled in the pertinent art based on the teachings herein, numerous changes may be made to the above described and other embodiments of the present invention without departing from its scope or spirit as defined in the appended claims. For example, alternate or supplemental sensors capable of sensing the low frequency vibrations or impulses generated by the heart include piezoelectric crystals, piezoelectric films, accelerometers, silicon pressure transducers, lasers, and other displacement devices. These low frequency vibrations also can be detected by electromagnetic field devices such as inductance transducers. Therefore, any of a number of sensing devices presently available or later developed may be used to augment or replace the sensors used for exemplary purposes herein. 
     Similarly, the particular hardware used for the acoustic diaphragm may be electronically augmented, and the earpiece, tubing, and housing may be replaced with hardware having similar functionality without departing from the scope and spirit of the present invention. 
     Likewise, the acoustic diaphragm itself may be replaced with a microphone, piezoelectric audio sensor, or similar mechanism, such that the processing of the infrasonic and audible cardiac motions may be done electronically to produce an audible output for the first time at one or more earpiece transducers. 
     In addition, a single sensor may be used to sense both infrasonic motions and audible sounds. For example, a piezoelectric sensing diaphragm may be used to sense both infrasonic motions and audible sounds when combined with a sensing protuberance capable of transmitting infrasonic motions and audible frequencies such that the audible sounds are not damped out by the mechanical loading of the sensing protuberance against the tissue of a patient. 
     Accordingly, this Detailed Description of the Preferred Embodiments is to be taken in an illustrative as opposed to a limiting sense.