Abstract:
A method and apparatus for measuring the heart rate of a patient. In one embodiment the apparatus includes a hollow bell mounted on a diaphragm. A transducer element is also positioned therein to receive sound transmitted through the diaphragm, convert the sounds into electrical impulses, and transmit the electrical impulses to a microprocessor. The electrical impulses have real-time wave patterns corresponding to the real-time wave patterns of the original sounds. The microprocessor performs mathematical operations on wave pattern data conveyed by the electrical impulses to determine a numerical value corresponding to the frequency of the wave patterns. This numerical value is sent to a digital output and displayed thereon.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to the field of acoustics, and more specifically to an electronic apparatus for the passive detection of a patient&#39;s heart rate. 
     BACKGROUND OF THE INVENTION 
     The heart rate is one of the most basic life signs of a patient. It is very important for a physician or other health care provider to have quick and accurate heart rate information when treating a patient, especially in an emergency situation. One time-honored method of obtaining the heart rate of a patient is by the auscultation and/or palpitation method, wherein the doctor, nurse, or other trained health care professional is required to feel or listen for a pulse, count the heart beats for a fixed period of time, and then calculate the pulse rate. One very familiar listening tool used for auscultation is the stethoscope. While providing the human touch, the auscultation and palpitation techniques are particularly prone to human error and further require the caregiver to focus on a counting task instead of the immediate needs of the patient. In an emergency situation, a doctor&#39;s time can be much better spent if he doesn&#39;t have to take time out to count the patient&#39;s pulse rate. 
     Another common technique for measuring a patient&#39;s pulse rate is by using electronic instrumentation. The heart rate may be detected by measuring rhythmic changes in the EMF potential generated by the periodic firing of the neurons of the cardiac system (electrocardiogram or ECG), by measuring vascular pressure changes coincident with the expanding and contracting of blood vessels with the heart beat (sphygmometer), and/or by measuring the changes in the Doppler shift of ultrasonic energy caused by the changes in the relative speeds of red blood cells reflecting the ultrasonic energy back at its source (Doppler ultrasound stethoscope or DUS). While more accurate than auscultation and palpitation, the above-mentioned instrumentation capable of performing these measurements tend to be bulky and cumbersome, and also require special preparations be made before measurements may be taken. Moreover, in the case of the ECG, specialized training is required to both administer the tests and to interpret the results. ECG monitors are thus found primarily in controlled clinical settings. 
     Currently, a patient&#39;s heart rate is either mechanically assessed in a clinical setting by bulky and expensive equipment or manually assessed in the field by a human caregiver. There remains a need for a method and apparatus for the measurement of heart rate in the field that does not require the caregiver to focus on the task of measuring the heart rate to the exclusion of other, potentially more important, tasks. The present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method and apparatus for measuring the heart rate of a patient. One form of the present invention includes a stethoscope having a hollow bell or cone chamber with a diaphragm for sound pickup. A transducer element is positioned within the bell chamber and operationally connected to a microprocessor. The transducer converts sound energy in the bell to electrical energy signals having the same patterns as the original sounds, and sends the electrical signals to the microprocessor. The microprocessor mathematically processes the electrical signals and produces an output signal corresponding to the frequency of the input signals. The output signal is numerically displayed on a screen. 
     One form of the present invention contemplates a combination, comprising: a stethoscope; a transducer operationally coupled to the stethoscope and adapted to convert sound impulses received by the stethoscope into electrical output impulses; a microprocessor adapted to receive the electrical output impulses from the transducer and further adapted to produce an microprocessor output signal; and a visual display adapted to receive and display the microprocessor output signal. 
     Another form of the present invention contemplates a combination, comprising: a sound pickup portion; a microprocessor operationally coupled to the sound pickup portion; and a visual display portion operationally coupled to the microprocessor; wherein the sound pickup portion is adapted to generate a first output signal; wherein the microprocessor is adapted to process the first output signal from the sound pickup portion and calculate a rate of rhythmic sounds; wherein the microprocessor is further adapted to produce a second electrical output signal corresponding to the rate to rhythmic sounds from the sound pickup portion; and wherein the visual display portion is adapted to display an output number corresponding to the second electrical output signal from the microprocessor. 
     Still another form of the present invention contemplates a method, comprising the steps of: placing a diaphragm coupled to a bell chamber against a patient&#39;s chest; amplifying the sound of the patient&#39;s heart beat in the bell chamber; channeling a portion of the sound energy to a microprocessor; counting the beats; calculating the rate of the beats; producing an electrical output signal corresponding to the calculated rate; and displaying the rate numerically. 
     One object of the present invention is to provide an improved passive heart rate monitor. Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the preferred embodiment of the present invention. 
     FIG. 2 is a sectional view of the embodiment of FIG. 1 taken along line A-A′. 
     FIG. 3 is a view of FIG. 1 coupled to binaural earphones. 
     FIG. 4 is a flowchart illustrating the method of passive detection of heart rate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     The stethoscope is a simple and familiar tool of the medical profession. The stethoscope is commonly found hanging around the health care provider&#39;s neck and operates by amplifying a patient&#39;s heart beat or other critical internal sounds and transmitting them through to the health care provider through earphones. The sound pickup is usually a hollow bell with a relatively flat diaphragm portion for contact with the patient&#39;s body. The diaphragm picks up the sound for the hollow bell to amplify. One or more hollow flexible tubes acoustically connect the bell to one or more earphones that are worn by the health care provider. 
     Another somewhat more sophisticated and somewhat less portable tool of the medical profession is the heart rate monitor. A typical heart rate monitor operates by measuring the changes in electromagnetic field (EMF) potential characteristic of the cardiac control function of the sympathetic nervous system. The heart is controlled by the routine and rhythmic firing of certain nerves of the sympathetic nervous system. Electrocardiograph (ECG) instrumentation can detect the rhythmic changes in nervous potential through electrodes attached to the exterior of the human body. The output signal so measured is the familiar PQRST waveform of the heart&#39;s beating action. The heart rate is obtained from the charting of the PQRST wave. 
     Alternatively, the heart rate may be measured by the sphygmometer, a device that measures the force and frequency of the pulse by detecting pressure changes in the circulatory system. A sphygmometer may include a pressure cuff or a pressure sensor that can be clamped onto a finger. The pulse is usually read as an analog output. The pulse rate is determined by counting the number of analog pulses for a given time period. While the sphygmometer can detect pulse rate, it is not as well suited for generating data regarding the regularity or normality of the heartbeat. 
     Another instrument that may be used to generate heart rate data is the Doppler ultrasound stethoscope (DUS). The DUS sends an ultrasonic signal at a frequency of several megahertz downstream a blood vessel along the direction of the blood flow. Some of the sound is reflected back to the transducer from moving blood cells and is frequency shifted according to their speed. The difference in frequency between the transmitted and reflected signals is produced as an audible tone proportional to the rate of blood flow. The rapid changes in the speed of the blood flow accompanying caused by the heart&#39;s beating action are heard as rhythmic changes in the tone. The heart rate may be determined from counting those changes. 
     Of the above-discussed instrumentation, the ECG unit produces the most accurate heart rate information. However, ECG machines are usually bulky and do not readily lend themselves to the quick determination of a patient&#39;s heart rate. In fact, the process of attaching the electrodes and taking a reading takes several minutes in the relatively sedate examination room setting. Moreover, the analysis of the PQRST wave is rather intricate and its interpretation requires a trained specialist. 
     The sphygmometer and the DUS both require manual counting and are thus both prone to manual counting error as well as the monopolization of the physician&#39;s time and attention while the heart rate is determined. Moreover, the DUS requires a gel-media interface between the ultrasound transducer and the patient and alignment of the transducer with a blood vessel. 
     The time honored, albeit low-tech, methods for measuring a patient&#39;s heart rate do not necessitate bulky specialized machinery but instead require the focused attention of the health care provider. A health care provider can manually determine heart rate by auscultation (listening to the heart beat/pulse and counting the number of beats in a fixed time) or palpitation (feeling the pulse and counting the number of beats in a fixed time). Both of these methods require the focussed attention of the health care provider while the counting is done, during which time no medical aid is given. In an emergency situation, immediate aid may be critical. However, the patient&#39;s heart rate might also be a critical piece of information required by the health care provider as necessary for providing proper aid. 
     Furthermore, the palpitation and auscultation methods are not as accurate as the mechanically determined techniques and are more prone to operator error. Moreover, conditions such as an irregular heartbeat are more difficult to detect and even more difficult to quantify by auscultation or palpitation. 
     The present invention combines the convenience and portability of the stethoscope with the mechanical accuracy of the mechanical instrumentation to provide a tool for the quick and accurate automated measurement of a patient&#39;s heart rate. The present invention allows the health care provider to focus their attention on the immediate needs of the patient while still obtaining the necessary heart rate information. 
     FIG. 1 illustrates the preferred embodiment of a stethoscope bell having a built-in passive heart rate detector  20 . The passive heart rate detector  20  includes a bell or cone portion  22  mounted to a diaphragm portion  24 . Diaphragm portion  24  is preferably relatively flat and acts as the base of bell portion  22 . Bell portion  22  also includes an acoustic connector  26 . A housing  28  is connected atop bell  22 . Housing  28  includes a display  30  and an activation control  32 . 
     FIG. 2 shows the interior of heart rate detector  20 . The bell portion  22  and diaphragm  24  define a bell chamber  34 . Sound entering through diaphragm  24  is amplified by chamber  34  and sent to a listener through acoustic connector or stem  26  and/or is converted to electrical impulses by transducer  36 . Transducer  36  is mounted within chamber  34 , and is also operationally coupled to microprocessor  38 . Transducer  36  converts incident sound wave patterns into electrical impulses having the same wave patterns. Transducer  36  then provides the electrical impulses as an input for microprocessor  38 . Microprocessor  38  is mounted within housing  28 , and is connected to battery  40 , actuator control  32 , transducer  36 , and display  30 . Electrical impulses received from transducer  36  provide real time wave pattern data for microprocessor  38  to operate upon. Upon actuation, microprocessor  38  performs mathematical operations on the data to transform real time wave patterns into frequency data. The frequency data is provided as a numerical output for the display unit  30 . 
     FIG. 3 illustrates a form of the present invention including acoustic tubing  42  connecting binaural earphones  44  to the bell chamber  34 . Tubing  42  is flexible and transmits sound from chamber  34  to the earphones  44 . Tubing  42  is connected to bell chamber  34  at stem  26 . 
     FIG. 4 is a block diagram illustrating the operational process of the present invention. In operation, heartbeat sounds enter bell portion  22  of heart rate detector  20  through diaphragm  24  placed against the patient&#39;s chest. The heartbeat sounds are isolated and amplified in bell chamber  34 . The heartbeat sound patterns are converted into corresponding electrical patterns by transducer  36  and sent to microprocessor  38 . The electrical patterns correspond to the real time waveforms of the sounds picked up by the stethoscope. Microprocessor  38  performs a Fourier transform on the electrical patterns to decompose the waveforms into frequency and energy values. Microprocessor  38  extracts frequencies from a range of about 0.5 to 5.0 Hz as representing the heart beat, based on the calculated frequencies and corresponding energies. It is expected that if diaphragm  24  is properly situated over patient&#39;s heart, the heart beat sound component of the signal will be much greater than the background component in the 0.5 to 5.0 Hz range. Microprocessor  38  calculates the heart rate from the frequency data obtained from a signal sample taken for a predetermined length of time. Microprocessor  38  then sends a numerical output signal to display  30  corresponding to the heart rate. 
     One form of the present invention is contemplated as having microprocessor  38  sufficiently powerful and loaded with software capable of distinguishing between various types of heart beat abnormalities (based upon a comparison with known abnormal heartbeat patterns) and displaying the same. The heartbeat sound pattern is comprised of the sounds of all of the individual heart valves opening and closing and the heart chambers being filled and emptied. It is well known that these heart activities are also represented by the PQST wave patterns generated electrically by the firings of cardiac neurons and mapped by the ECG. The shape and timing of the electrical patterns generated by microprocessor  38  from the heartbeat sound patterns may be compared to preselected PQST patterns for regular heartbeat patterns as well as to preselected PQST patterns for such irregularities as heart murmur, irregular rhythm, incomplete valve closure, cardiac arrest, and the like. Microprocessor  38  can be adapted to store Fourier transforms characteristic of one or more types of abnormal heartbeat patterns and to compare them to the Fourier transform of the heartbeat sounds from the patient. The degree of matching necessary to flag a heartbeat as abnormal may be preselected (hardwired) or may be variable. When microprocessor  38  flags a heartbeat pattern as abnormal a message is displayed on display  30 , alerting the health care provider that the heartbeat is abnormal and what, if any, known type of abnormal pattern was matched. 
     Another form of the invention is contemplated as having a microprocessor  38  adapted to extract frequencies characteristic of other bodily functions, such as respiration or the like. 
     Bell portion  22  of the preferred embodiment of the present invention may be formed from stainless or surgical steel, plastic, resin or any other structural material having adequate sound conduction properties. Diaphragm portion  24  may be formed from epoxy resin, steel, plastic or any convenient material having adequate sound conduction properties. Transducer element  36  may be formed from any convenient monolithic, stacked or composite ceramic or polymeric or combination piezoelectric material having sufficient sensitivity. Display unit  30  may be a liquid crystal screen or the like. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.