FIELD OF THE INVENTION

The following pertains to the field of cardiac health in general and to devices for diagnosing the heart's condition in particular.

BACKGROUND OF THE INVENTION

A number of devices, instruments and systems are at the disposal of physicians for diagnosing the heart's various abnormalities. Each means has advantages, disadvantages, field of application, the stage in the medical history of a patient and the cost associated with each. One of the earliest known means for detecting or diagnosing cardiac conditions is feeling the patient's pulse by the physician. Later, means for listening to the sounds of the patient's heart were developed using which a trained physician could make at least a primary diagnosis about the patient's heart condition. A more detailed, perhaps also more expensive, diagnostic method could be decided upon based on such an initial diagnosis. Especially in rural areas and for the poor, at least in many developing and underdeveloped countries, such primary diagnosis would be of great value, based on which further tests could be decided upon, saving valuable time and resources for the patient.

The United States patent, US 7,445,605 B2 discloses a method and means for diagnosing a patient's heart condition by sensing quantities associated with the apical pulses sensed by implanted sensors. The patent discloses systems, devices and methods for detecting and monitoring cardiac dysfunction. The devices include motion sensors for detecting signals representative of the total movement of the heart, and of the apex of the heart in particular. According to the disclosures therein, the devices are intra-corporeal, usually implanted, and may be used for continuous, automatic monitoring, thereby providing early diagnosis of acute myocardial ischemia or infarction.

SUMMARY OF THE INVENTION

According to the device disclosed in the prior art document, the sensors are intra-corporeal. Such a device has the disadvantage that the patient has to be implanted with such sensors and it is useful for monitoring only a patient so implanted. The disclosed device addresses this disadvantage and others.

The device disclosed herein is a device for diagnosing a cardiac condition of a test subject, comprising at least one sensor for sensing an effect of the test subject's heartbeat on an external surface of the test subject's thorax and generating a sensor signal

representative of it, a comparison unit for comparing the sensor signal with at least a reference signal representative of an effect of a heartbeat on an external surface of a healthy subject's thorax, a decision unit for making a decision based on the comparison and a user interface for conveying the decision to a user.

Herein, the term 'test subject' is used to signify a person undergoing tests using the device disclosed herein, to ascertain his or her cardiac condition. The term 'user' could be any person using the device and is normally a physician or a care giver or a clinical assistant using the device to test the test subject. It is to be understood that one could use the device to test oneself and in which case the test subject is the user too.

The device receives the sensor signal from its sensor that senses the effect of the test subject's heartbeat on the surface of the test subject's thorax, when placed in contact with it. Various types of transducers could be used for the purpose including, but not limited to, a piezoelectric transducer, a strain gauge, inductive transducers, capacitive transducers, etc. The signal from the sensor may be digitized and stored and then retrieved for

comparison. The sensor signal is compared with a reference signal stored in a memory unit, the reference signal having been obtained in a similar manner as described above but, from a normal or healthy subject. The differences between the two are used to diagnose the pathology causing the differences. The result or diagnosis is conveyed to the user, for instance by displaying it on a display unit.

A method of diagnosing a cardiac condition is also disclosed herein. The disclosed method is a method of diagnosing a cardiac condition of a test subject, the method comprising a sensing step of sensing at least an effect of the test subject's heartbeat on an external surface of the test subject's thorax, for producing a sensor signal, a comparison step (733) of comparing the sensor signal with at least a reference signal representative of an effect of a heartbeat on an external surface of a healthy subject's thorax, a deciding step (735) of making a decision based on the comparison and a conveying step (737) of conveying the decision to a user.

In this method the sensor signal received from the sensor in contact with the external surface of the test subject's thorax is compared with a reference signal acquired similarly from a healthy subject. Decisions are made about the condition of the heart and its surroundings based on the comparison.

Even though the method described above may yield a reliable diagnosis, when the cardiac apical impulse is the signal being sensed, it may be preferable to acquire the sensor signal when the sensor is placed on the external surface of the test subject's thorax at a position substantially closest to the cardiac apex. This may improve the reliability of the diagnosis. Further, the knowledge of the very location of the cardiac apex, relative to certain landmarks of the thorax may provide valuable information about the magnitude of the abnormal cardiac condition, if any, in the test subject.

A method of aiding the user to place the sensor at a point on the external surface of the test subject's thorax is also disclosed herein. The method described above further comprises aiding a user in positioning the at least one sensor on the external surface of the test subject's thorax to obtain an optimum sensor signal, prior to the acquiring step, the method of aiding comprising the steps of a receiving step of receiving three or more sensor signals from three or more sensors arranged in a predefined geometric relationship to one another and being placed on the external surface of the test subject's thorax and in contact with it, in an initial location a comparison step of comparing at least the amplitudes of the three or more sensor signals with one another a prediction step of predicting, based on the comparison, a new location on the external surface of the test subject's thorax, for a predetermined one of the three or more sensors, from which new location, the predetermined sensor is estimated to generate a sensor signal of at least a larger amplitude than from the current position and a conveying step of conveying an information about the predicted new location to a user.

In the above description, the term optimum may mean substantially the largest amplitude of the sensor signal obtainable from the external surface of the test subject's thorax. However it is to be understood that it may also mean a signal with the largest Signal to Noise Ratio. It may also be that the location on the external surface of the test subject's thorax the signal from where has the largest amplitude also simultaneously has the largest signal to noise ratio. In case the SNR is chosen as the criterion to decide the optimum, the final location of the sensor may not indicate the position on the external surface of the test subject's thorax, substantially directly under which the cardiac apex lies. In that case the user may not use the indication of the position as additional input for the diagnosis made by the physician. Further, a computer program product is also disclosed herein, which, when run on a computer, carries out the method disclosed herein. Such a computer program product for carrying out a method for diagnosing a cardiac condition of a test subject comprises instructions for sensing at least an effect of the test subject's heartbeat on an external surface of the test subject's thorax, for producing a sensor signal, comparing the sensor signal with at least a reference signal representative of an effect of a heartbeat on an external surface of a healthy subject's thorax, making a decision based on the comparison and conveying the decision to a user.

Yet another computer program is disclosed, which, when run on a computer, carries out the disclosed method of estimating a new position for the sensor from which a better sensor signal is likely to be obtained. The term better signifies that the signal is more likely to yield a more reliable diagnosis when used in applying the disclosed method. Such a computer program for a method for diagnosing a cardiac condition of a test subject comprises instructions for receiving three or more sensor signals from three or more sensors arranged in a predefined geometric relationship to one another and being placed on the external surface of the test subject's thorax and in contact with it, in an initial location, comparing at least the amplitudes of the three or more sensor signals with one another, predicting, based on the comparison, a new location on the external surface of the test subject's thorax, for a predetermined one of the three or more sensors, from which new location, the predetermined sensor is estimated to generate a sensor signal of at least a larger amplitude than from the current position and conveying an information about the predicted new location to a user.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will be described in detail hereinafter by way of example on the basis of the following embodiments and implementations, with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic representation of an embodiment of the disclosed device with a single sensor,

Fig. 2 is a representation of the cardiac apical impulse signals, one signal from a normal heart and two signals with abnormal cardiac conditions,

Fig. 3 is a schematic representation of an embodiment of the disclosed device with multiple sensors,

Fig. 4 is a schematic representation of an embodiment of the disclosed device with multiple sensors and an updating unit for the reference signal, Fig. 5 is a schematic representation of an embodiment of the disclosed device with multiple sensors and an external communication unit,

Fig. 6 is a representation of an embodiment of the disclosed device in a perspective view,

Fig. 7 is a representation of a method of diagnosing a cardiac condition, as disclosed herein, and

Fig. 8 is a representation of a method of aiding a user in positioning a sensor on the external surface of the test subject's thorax to obtain an optimum sensor signal.

A common reference numeral in different figures refers to the same element in all the different figures.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 is a schematic representation of an embodiment of the disclosed device using a single sensor, shown generally as 100. Sensor 101 is for sensing the effect of a heartbeat of a test subject on the surface of the test subject's thorax, hereinafter referred to as the cardiac signal. The signal output from the sensor 101 is processed and analyzed in an analyzer 304. The analyzed signal is compared, in the comparison unit 109, with a reference signal stored in the memory unit 107. The reference signal is a cardiac signal acquired from a healthy subject. It is to be understood that a healthy subject in this context refers to a human subject without any cardiac pathology as determined by other diagnostic means. It could also mean a reference signal synthesized by acquiring such signals from a number of healthy human subjects. The differences between the two signals, if any, may be indicative of a particular pathological condition of the test subject's heart. The decision unit 111 makes a decision based on the detected differences. The decision unit 111 may make the decision by selecting one or more condition or conditions of the heart that could cause the differences, from a look up table, for instance. This information is conveyed by the user interface driver 113 on the user interface, for instance a display 115. The device may, however, display that the test subject's heart is normal if there are no significant differences between the sensor signal and the reference signal.

The effect of the heartbeat on the surface of the thorax may be of two types. One is caused by the movement of the apex of the heart and is called a cardiac apical impulse. The other is caused by the vibrations in the heart muscle or the movement of the blood in the cavities of the heart, for instance. They are descriptively referred to as thrills, murmurs, purrs, and taps, for instance. The former signal is a sub-audio frequency signal whereas the latter ones are in the audio frequency range. Thus the sensor could be a specialized sensor sensitive to either of the two frequency ranges or a common sensor with a broad bandwidth capable of sensing either of the signals mentioned.

Since the transducer is placed on the surface of the test subject's thorax, the strength of the signal generated by the transducer may not be the optimum one due to various reasons. The most important of them is the location of the transducer on the external surface of the patient's thorax. Further, subcutaneous fat, hydration level, muscle tone, skin tone, etc., of the test subject may also influence the signal produced by the transducer. Since the results of the analysis and comparison of the signal are important for a reliable diagnosis, it is important that as good a signal as possible signal is picked up. This can be controlled, for example, by the location of the transducer on the test subject's thorax, which is under the user's control.

Thus, to assist the user in positioning the sensor at an optimum position on the test subject's thorax, the signal from the sensor may be conveyed to the user interface 115 for being displayed. In one variant, the sensor signal, after suitable processing, if need be, may be displayed on the display as a real time graph of the instantaneous amplitude versus time. The user may find the optimum position by placing the device at various positions on the test subject's thorax and obtaining substantially the largest possible signal on the display.

Alternatively or additionally, the signal could be processed and amplified by an audio signal processor unit 103 and the output signal 117 may be used to drive a loudspeaker or earphones or headphones and place the device on the test subject's thorax to get the loudest possible signal. This, of course, is a straightforward process for the audio frequency signals. Since the cardiac apical impulse is a sub-audio frequency signal it needs to be converted into a form that is audible. The sensor signal may be fed to a voltage to frequency converter whose output frequency is always in the audio frequency range for all values of the input signal. Alternatively an audio frequency carrier signal may be amplitude modulated with the sensor signal to obtain an audible signal.

The sensor signal may be compared with the reference signal in various ways. The signal may undergo Fourier Transformation and the resultant spectrum could be compared with the spectrum of the reference signal in the memory 107. The memory may, of course, store the spectrum of the reference signal instead of the reference signal in any other form. The reference signal may be stored in digital form as well and may undergo Fourier Transformation. Alternatively, the sensor signal may be compared with the reference signal in the time domain. The amplitudes, phases and wave shapes of the two signals, for example, could be compared. It is also possible to compare the signals in a combination of these two methods.

In Fig. 1, the sensor 101 is shown as a separate component connected to the unit. However the sensor may be fixed to the body of the device in a permanent or semipermanent or detachable way such that the whole device may be placed on the test subject's thorax and the sensor comes into contact with the surface of the test subject's thorax. To enable this, the sensor is affixed to the device on what will be referred to as the obverse face of the device in the subsequent description, which is the face opposite to and substantially parallel to the face having the user interface. Thus when the device is placed on the test subject's thorax, the sensor is in contact with the surface of the thorax and the user is able to see the user interface. The position of the sensor is suitably indicated on the front face, in other words, the face having the user interface, in such a manner that the user is able to know the position of the sensor on the surface of the test subject's thorax as the crossed dotted line indicated as 627 in Fig. 6 a, for instance. This provides further information to the user for diagnosis, especially in the case of the Cardiac Apical Impulse signals, as follows.

Various pathologies of the heart displace the apex of the heart from its normal position in the rib cage. Normally the apex beat is most pronounced in the fifth left intercostal space within or medial to mid-clavicular line. In case of heart enlargement, also called cardiac hypertrophy, for example, the apex of the heart would have moved away from its normal position. The extent and direction of the displacement of the apex itself provides the physician valuable information about the condition of the heart. Thus a physician could use the information available from the location of the sensor when the position of maximum or the best signal is achieved. With the help of this information a physician would know the extent of the shift of the apex of the heart away from the normal position and thereby diagnose the cardiac pathology affecting a subject. A large number of pathologies may be diagnosed by the physician with this information viz., the extent and direction of the shift of the apex of the heart from the normal position. For example, the apex may be displaced laterally in test subjects with chest deformity, or because of mediastinal shift secondary to large pleural effusion, tension pneumothorax (away from the affected side) or

pneumonectomy or lung collapse (towards the affected side) . In these situations, the trachea may also be deviated. Thus, by locating the position of the maximal apical signal, the physician may be able to diagnose various pathological conditions of the heart of a subject. Thus, the device not only carries out the diagnosis based on the cardiac apical signal but also aids a physician in diagnosis based on the determined location of the apex of the heart.

Although this aid to the physician is described with reference to the present embodiment, it is to be understood that such assistance is available from all the embodiments described further. Thus this feature of the disclosed device is not discussed further with reference to the other embodiments.

Fig. 2 is a representation of the apical signal. It shows the normal cardiac apical signal and two signals indicative of two abnormalities. It can be seen from these signals that the differences between the reference and the acquired signals could lead to the diagnosis of the pathology of the heart causing the differences.

Based on this knowledge, cardiac apical impulse signals from patients whose heart pathology has been determined by other means, for example CT or MRI, may be collected, analyzed and processed using statistical methods. Similarly, signals from individuals whose hearts are deemed normal by other means are also collected, analyzed and processed using statistical methods. The signals from the hearts of particular pathologies are compared with the signal from the hearts of normal individuals to determine the deviations. With this, a map of the correlation between the type and extent of deviation and particular pathologies may be developed. This map is used further to test other unknown test subjects to determine the pathology or pathologies affecting the test subject's heart.

Similarly, the other sounds of the heart obtained from healthy individuals and stored as references could be used to compare the sounds from a subject's heart. In this case, because of the nature of the sounds, the comparison of the spectrum of the sensor signal from a subject and the spectrum of the reference signal may be appropriate. Alternatively, the spectrum of the sensor signal from the test subject's thorax may be analyzed to determine the presence and amplitudes of certain spectral bands to determine the various types of sounds.

Fig. 3 shows a schematic representation of another embodiment of the device disclosed herein, shown generally as 300. As shown in Fig. 3, this embodiment has more than one sensor. Fig. 3 shows five sensors 101. The dotted arrow in Fig. 3 indicates an axis of the device, referred to as the axis of the device heretofore and the arrowhead is near the edge of the device that is referred to as the top edge of the device in the following description. The edge of the device opposite to the top edge is referred to as the bottom edge of the device.

The five sensors are arranged in a semicircle. This means that the centers of the sensors are located on one half of the circumference of a circle. Further, the semicircle is so oriented that the diameter of the imaginary circle defining the semicircle is parallel to the top edge of the device. A first sensor is located at the point on the semicircle where an imaginary line passing through the centre of the imaginary circle and is parallel to the axis of the device intersects the semicircle. Two second sensors are located at the end points of the semicircle. Two third sensors are located on the semicircle equidistant from the first sensor and each of the second sensors.

When a test subject is to be tested with the device, the test subject is normally made to lie supine and the device is placed on the test subject's thorax. It is to be noted that the device is placed on the left side of the test subject's chest where the heart is normally located - except in case of Dextrocardia. The device is placed on the test subject's thorax such that the top edge of the device is towards the head of the patient and is substantially parallel to the Left-right (DextroSinister) axis and the axis of the device is substantially parallel to the head to toe (Anteroposterior) axis. The device is placed at a position such that the first sensor is as close to an imaginary line joining the nipples of the test subject. By this it is ensured that the apex of the heart is away from the bottom edge of the device and towards the abdomen of the test subject.

When the device is placed on the test subject's thorax such that the sensors are in contact with its surface, each sensor picks up the cardiac apical impulse signal. The signals are analyzed and depending on the relative strengths of the signals, for instance, a better position for the placement of the device on the thorax may be estimated as follows. The relative strengths of the sensor signals from the two second sensors and the two third sensors could be used to determine the required direction of movement of the device in a direction substantially parallel to the transversal plane. The movement in this direction is to achieve substantially equal signal amplitude from each of the second and third sensors. The movement in this direction is stopped once the sensor signals from each of the second and each of the third sensors are substantially equal. Further movement of the device is only in the direction substantially parallel to the head-to-toe plane. During this movement, the aim is to increase the strength or magnitude of the sensor signal from the first sensor while maintaining the strengths of the signals from the second and third sensors substantially equal. The direction of suggested movement may be indicated on the display 115 as an arrow 116 as shown in Fig. 3. This indicates to the user that the device must be moved to a new location in the indicated direction.

Alternative methods may be suggested by a skilled person to achieve the same result. One possible alternative method is triangulation, for instance. Every time the user moves the device to the new location indicated, the device may again estimate a better position and indicate the direction as described before. By further iterations of these steps, the device will guide the user to get the best signals from the first sensor.

Even though, an arrangement of five sensors in a semicircle is described above, neither the number nor the shape is essential for the invention. For example, three sensors, arranged at the apex and ends of a 'V shape, as indicated by a dashed line in Fig. 3, could also be used with advantage.

Additionally the device may vary the size of the arrow to indicate whether the movement required is small or large. Thus when the arrow becomes negligibly small it may indicate that the optimum or near optimum location has been reached.

Once the best or the optimum position is achieved, signal from the sensor closest to the cardiac apex, viz., the first sensor may be compared with the reference signal to determine the pathology affecting the test subject's heart, as described earlier.

Fig. 4 shows the schematic diagram of another embodiment of the disclosed device 400. In this embodiment the reference signal stored in the memory 107 is dynamically updated every time a test subject is tested with the device. The device includes a statistical processing unit for updating the reference signal based on the comparison. Whenever a test subject is tested with the device it acquires and processes a signal representative of the cardiac apical pulse of the test subject. When this is compared with a reference signal the difference between the reference signal and the sensor signal may indicate that the test subject's heart has a pathological condition. Depending on the characteristics of the difference the pathology may be determined. If however the differences between the reference signal and the signal received from the sensor is too small to indicate a pathological condition, then, the statistical processing unit 418 updates the reference signal by statistically merging the two signals. The term merging is used herein to indicate that appropriate statistical operations are carried out on the two signals to obtain a single resultant signal, which until updated again is used as the reference signal. However, it is possible that the statistical merging takes place only if the user allows it. That is to say the merging takes place only when the newly acquired signal is declared normal by the device and the user, a physician for example, inputs a user input to allow the merging.

Fig. 5 shows another embodiment of the device disclosed herein. Even though hitherto a single reference signal has been mentioned, in fact, the device may have more than one reference signal stored in it. The reference signal may be selected for use for comparison at least based on one of age and sex of the test subject. Before the device is used on a test subject, an appropriate reference signal may be selected from a set of reference signals, depending on user inputs. The user inputs may be provided through a user interface, a key pad 419 for example.

The user input could also be used to give other commands to the device. For instance, when the device is first placed on the test subject's thorax, the device could be commanded to assist the search and location of the best position for the device on the thorax as described before. Once the user is satisfied that the best location has been found or when the device determines so, the device could be commanded to proceed with acquiring the signal, analyzing it and comparing it with the selected reference signal and displaying the message based on the comparison.

Further, the apical impulse or other heart sounds could be sensed with advantage, when the test subject has assumed different physical attitudes or postures. Some pathologies are better revealed when the test subject is supine whereas some others when the patient is resting on either side or leaning sideward. The initial or the first test could be conducted when the test subject is supine. Depending on the result or results of the test, the test subject could assume one or more of the other positions in sequence and the test repeated in each position. Thus, the user interface could be used to input the position or physical attitude of the patient. Thus the reference signal could be selected based on the physical attitude of the test subject also.

Even though the disclosed device has been described hitherto as a device for testing the cardiac condition, in a further embodiment it is configured to be used as a monitoring device. The device is provided with securing means (not shown) to secure the device externally to the test subject's thorax such that the device may continuously or periodically receive the sensor signals and compare them with the reference signal and based on the comparison, display a suitable message on the user interface. Fig. 5 shows such a device schematically. The device includes a communication unit 521 for communicating with a remote location. This communication device may be for wired or wireless communication. The disclosed device may communicate the results of the comparison to a remote station 523 say, a care giver's station in a hospital environment. In such a case the device itself may be configured not to display the messages but only to display the assistance needed to the user for the proper location of the device on the thorax of the patient. The communication device could also receive user inputs that are normally input by the user through the user interface, for instance the key pad 519. It is to be noted that the exact configuration of a device according to this embodiment may have various forms. That is, the device could have no key pad and all the commands are received from the remote station. Many such variations may be thought of based on this disclosure and all such variations are within the scope of this disclosure.

Fig. 6 shows three views of an exemplary embodiment of the device disclosed herein. Fig. 6 a, which is a front view of the exemplary device, shows the display 115 displaying an arrow to guide the user to move the device in the direction indicated by it. Fig. 6 b shows, exemplarily three sensors arranged on the obverse side of the device. Fig. 6 c shows the same device displaying a message to the user. Exemplarily, three connectors 625 are shown representing the output ports for external communication and one of them could be an appropriate audio connector for connecting to the headphones and such. These are shown as an example and the device may have less or more of them and in any convenient position on the device. Figs. 6 d and e show exemplary arrangements of sensors at the obverse side of the device that may be used advantageously.

Further, with reference to Fig. 7, a method 700 of diagnosing a cardiac condition of a test subject, the method comprising, an acquiring step 731 of acquiring at least one sensor signal generated by a sensor sensing an effect of a test subject's heartbeat on the external surface of the test subject's thorax, a comparison step 733 of comparing the sensor signal with a reference sensor signal generated by a sensor sensing an effect of a healthy subject's heartbeat on the external surface of the healthy subject's thorax, a deciding step 735 of making a decision based on the comparison and a conveying step 737 of conveying the decision to a user.

Even though the method described above may yield a reliable diagnosis, in the case where the signal representative of the cardiac apical impulse is being used, it may be preferable to acquire the sensor signal when the sensor is placed on the external surface of the test subject's thorax substantially under which the cardiac apex lies. This may improve the reliability of the diagnosis. Further, the knowledge of the very location of the cardiac apex, relative to certain landmarks of the thorax may provide valuable information about the magnitude of the abnormal cardiac condition, if any, in the test subject.

Thus a method of estimating a new position that is estimated to provide a better signal than the signal from the current position is also disclosed herein, with reference to Fig. 8. The method, generally shown as 800, comprises aiding a user in positioning the at least one sensor on the external surface of the test subject's thorax to obtain an optimum sensor signal, prior to the acquiring step, the method of aiding comprising the steps of, a receiving step 841 of receiving three or more sensor signals from three or more sensors arranged in a predefined geometric relationship to one another and being placed on the external surface of the test subject's thorax and in contact with it, in an initial location, a comparison step 843 of comparing at least the amplitudes of the three or more sensor signals with one another, a prediction step 845 of predicting, based on the comparison, a new location on the external surface of the test subject's thorax, for a predetermined one of the three or more sensors, from which new location, the predetermined sensor is estimated to generate a sensor signal of at least a larger amplitude than from the current position and a conveying step 847 of conveying an information about the predicted new location to a user.

In the above description, it is to be understood that even though the

positioning of the sensor alone is described, in embodiments in which the sensor is affixed to the device or is integral to the device, as described, the whole device is moved to a new position as estimated according to the method described. Even though the description is about one application of the method, it is to be understood that it may be repeated several times to achieve the best possible results before the sensor signal is acquired and compared with the reference signal for carrying out the diagnosis.

In embodiments wherein there is more than one sensor, the signals from all the sensors are used to estimate the new position for a predefined one of the sensors. This is made possible from the knowledge that the amplitude of the apical signal received from each sensor is dependent on the distance between the senor and the cardiac apex. Therefore, by comparing the signal amplitudes from the different sensors, the direction in which the sensors have to be moved to obtain the apical signal with the maximum amplitude from one of them, may be estimated.

Further, a computer program product is also disclosed that, when run on a computer, carries out the method disclosed herein. The disclosed computer program product is for carrying out a method for diagnosing a cardiac condition of a test subject that comprises instructions for acquiring at least one sensor signal generated by a sensor sensing an effect of a test subject's heartbeat on the external surface of the test subject's thorax, comparing the sensor signal with a reference sensor signal generated by a sensor sensing an effect of a healthy subject's heartbeat on the external surface of the healthy subject's thorax, making a decision based on the comparison and conveying the decision to a user, when the computer program is run on a computer. Yet another computer program is disclosed that, when run on a computer, carries out the disclosed method of estimating a new position of the sensor from where a better or optimum sensor signal than the one being received from the current location, may be received. Such a computer program for a method for diagnosing a cardiac condition of a test subject comprises instructions for receiving three or more sensor signals from three or more sensors arranged in a predefined geometric relationship to each other and placed on the external surface of the test subject's thorax and in contact with it in an initial location, comparing at least the amplitudes of the three or more sensor signals with one another, predicting, based on the comparison, a new location on the external surface of the test subject's thorax, for a predetermined one of the three or more sensors, from which location, the predetermined sensor is estimated to generate a sensor signal of at least a larger amplitude than from the current position and conveying an information about the predicted new location to a user, when the computer program is run on a computer.

The computer program disclosed herein may reside on a computer readable medium, for example a CD-ROM, a DVD, a floppy disk, a memory stick, a magnetic tape, or any other tangible medium that is readable by a computer. The computer program may also be a downloadable program that is downloaded, or otherwise transferred to the computer, for example via the Internet. The computer program may be transferred to the computer via a transfer means such as an optical drive, a magnetic tape drive, a floppy drive, a USB or other computer port, an Ethernet port, etc.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. A person skilled in the art may change the order of steps or perform steps concurrently using threading models, multi-processor systems or multiple processes without departing from the disclosed concepts. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The disclosed method can be

implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.