GB2426586A - Passive acoustic blood circulatory system analyser - Google Patents

Abstract

A device 50 for analysing the blood circulatory system comprises a probe 100 with a microphone 106 which detects the acoustic signal generated by blood flowing in the blood vessel 104 (e.g. carotid artery in the neck). The probe 100 is connected to processing circuitry 108 which analyses the blood flow through the vessel 104. The device 50 may determine whether the blood flow within the vessel is occluded and can distinguish between stenosis and a plauque. The device 50 may compare the acoustic signal with previously stored signals. Abnormal heart rhythms, conduction defects and heart valve defects can be diagnosed.

Description

ACOUSTIC BLOOD CIRULATORY SYSTEM ANALYSER This invention relates to an acoustic blood circulatory system analyser for human or animals and in particular, but not exclusively, to an analyser for the carotid artery in the human neck. The phrase 'blood circulatory system' is intended to include all parts of the human or animal body through which blood circulates including arteries, veins and capillaries. Hereinafter, for simplicity, the phrase 'blood vessel' will be understood to include all parts of the blood circulatory system. Although embodiments of this invention have wider applicability it is convenient to describe it in relation to an analyser for the carotid artery found in the human neck. Strokes are one of the main causes of medical emergencies worldwide with between 22 million and 60 million strokes being estimated each year. Each year one in every 100 people over 70 years old in the UK will suffer from a stroke. Such strokes may arise from fragments of an atheromatous plaque becoming dislodged in the carotid artery; the fragment subsequently travelling to the brain causing a stroke, or they may arise from blood clots that are formed around the plaque and in which the clot subsequently blocks or restricts blood flow to the brain tissues. Short term TIA's (Transient Ischaemic Attacks) otherwise known as ministrokes may also occur and which may include symptoms such as amaurosis fugax. Full strokes can lead to long term consequences such as partial paralysis. The blocking of the carotid artery by atheromatous plaques in most instances remains undiagnosed until the patient presents to their GP with symptoms. This generally occurs at a relatively advanced stage of the condition, when the artery is about 70% blocked. At such a late time in the course of the condition only one effective procedure exists for its treatment which is called a carotid endarterectomy. This is a highly invasive procedure that carries risks (e.g. risk of facial nerve palsy, postoperative haemaotmas and even strokes occurring during the procedure itself). The procedure involves removal of the athermomatous plaque within the artery by making an incision in the artery wall itself to facilitate mechanical removal of the plaque material. Previously it has been possible to study blood flow through a vessel using an ultrasound device, which emits high frequency acoustic waves into a patient and uses the reflected sound to model the tissue, including the blood, through which the acoustic waves have passed. However, such machines suffer from a number of disadvantages: they can be very costly, the results provided therefrom can be hard to interpret and require a skilled operator and cannot generally be used to determine an occlusion of less than roughly 60%, and high frequency acoustic waves are emitted which some may consider to be harmful to the patient. Further, prior art machines have tended to have a high power consumption and as such are not generally suitable for providing portable devices. According to a first aspect of the invention there is provided an acoustic blood circulatory system analyser comprising an acoustic input means arranged to receive at least one of an acoustic input generated by blood flowing through a blood vessel and data representative of an acoustic input generated by blood flowing through a blood vessel and generate a signal therefrom, a processing circuitry arranged to receive and process the signal, the processing performed by the processing circuitry being arranged to analyse the blood flow through the vessel and generate an output from an output means of the analyser indicative of a one or more parameters of the blood flow. Such an analyser is advantageous because it is a passive device and does not generate any electromagnetic, or acoustic, radiation which is subsequently passed into the patient on which it is being used. Further, because it is a passive device it will generally be the case that its power consumption can be made lower than an active device and as such it may be more suitable for powering from a portable power supply such as a battery. It will be appreciated that the term acoustic relates to the what may generally be termed sound waves. The frequencies that are intended to be covered by this term extend beyond the frequency range that a human ear may be able to hear. For example, the acoustic input means may be able to receive and generate a signal from roughly a few tenths of a Hertz to roughly a 100kHz. In other embodiments, the range may be roughly 1Hz to 50kHz. In some embodiments the range may be restricted to roughly 5Hz to 20kHz. In one, perhaps a preferred embodiment, the processing performed by the processing circuitry is arranged to determine whether the blood flow within the vessel is occluded or at least partially occluded. Such a device is advantageous since it should to be able to diagnose blockages such as plaques at a much earlier stage before they give rise to symptoms via extensive occlusion of the blood vessel such as the carotid artery. Such early diagnosis may allow for treatment for example, the patient could be advised about effective measures such as life style changes (e.g. diet, exercise) to avoid later catastrophe. The device may allow early diagnosis of atheromatous plaques and/or other conditions, and may also facilitate non-invasive easily available monitoring when the patient is located at places such as health centres, GP surgeries and even within the home. Conveniently, the processing circuitry may be arranged to compare the signal with one or more previously stored signals in order to analyse the blood flow through the vessel. Such a comparison is convenient because it provides an analyser which may be simple to use. In alternative, or additional, embodiments the analyser may be arranged to time the occurrence of one or more predetermined features of the signal. For example, it is likely that the signal will comprise a feature which corresponds to the systolic pressure wave generated by the heart. It is further likely that the signal will comprise a feature which corresponds to the diastolic pressure wave generated by the heart. The processing circuitry may be arranged to time the relative and/or the absolute times at which the features corresponding to the diastolic and the systolic pressure waves occur. It is likely that the feature within the blood flow (e.g. the pressure pulse generated by the systolic or diastolic pressure waves) will generate a set of known frequencies and amplitudes which identify that feature within the signal. The processing circuitry may be arranged to monitor the signal for these frequencies and/or amplitudes. An advantage of using features in this manner is that it may be possible to diagnose problems with the heart. For example, it may be possible to determine abnormal heart rhythms such as those caused by conduction defects as well as those caused by abnormal rate. Such a device may be arranged to diagnose a variety of other conditions such as those that follow in the non-exhaustive list: aortic stenosis; mitral regurgitation; ventricular septal defect; atrial septal defect; mitral stenosis; aortic regurgitation The analyser may be arranged to use the presence of one or both of the features corresponding to the systolic and diastolic pressure waves to determine whether the vessel is blocked.It has been found that the signal received from an unblocked vessel (i.e. a healthy vessel) is similar to the signal received from a blood vessel which is substantially blocked (e.g. there is an absence of turbulent flow) but that in the blocked vessel there is an absence of both of the features generated by the systolic and diastolic pressure waves from the signal. Thus, it can be advantageous to arrange the analyser to use these features to be able to differentiate between a healthy and a substantially blocked vessel. The blood vessel will generally be an artery and may in one particularly preferred embodiment be the carotid artery. Preferably, the processing circuitry is arranged to sample the signal and further may be arranged to digitise the signal. The processing circuitry may be arranged to perform signal processing on the signal in order to generate the output. In a particular embodiment the processing circuitry may be arranged to perform a Fast Fourier Transform (FFT) on the signal in order to change the signal into the frequency domain as will be appreciated by the person skilled in the art. In other embodiments the processing circuitry may be arranged to use different transforms or alternatively or additionally may be arranged to use an auto correlation function. For example, the processing circuitry may be arranged to use Laplace or Discrete Fourier Transforms. The processing circuitry may be arranged to generate a spatial frequency profile from the signal. Conveniently, the processing circuitry is arranged to generate a table of frequencies and/or amplitudes from the signal and generally from the signal processing performed on the signal. The skilled person will appreciate that an occlusion in the blood vessel will generate turbulent flow within the blood therein which will cause an amplitude at frequencies at which no, or a low, signal would usually be expected. Using the magnitude of the amplitude at one or more predetermined frequencies it may be possible to determine the size and/or shape of the occlusion within the blood vessel. The processing circuitry may be arranged to generate a curve from the amplitudes and/or frequencies. The curve may be output by the output means. However, in alternative embodiments the curve may be generated as a construct within the processing circuitry and/or a memory accessible by the processing circuitry. The processing circuitry may be arranged to determine from the processing performed on the signal, and may be from the curve, the profile of an occlusion within the blood vessel. Conveniently, the device is arranged such that reception of the signal, by the signal processor, is synchronised with an external event. In a preferred embodiment the device is arranged to synchronise the sampling with the heart beat detectable within the blood vessel. If the acoustic input means is arranged to receive an acoustic input then the analyser may be arranged to sample the signal generated therefrom. In some embodiments the acoustic input means may comprise a microphone, or other sound transducer such that a sound (i.e. an acoustic input) is captured thereby and converted into an electrical signal. Alternatively, the acoustic input means may comprise an analogue recording device arranged to record an analogue signal. In other embodiments the acoustic input means may comprise a digital input means arranged to receive digital data representative of an acoustic input generated by blood flowing through a blood vessel. The digital input means may comprise any form of machine readable medium. Such embodiments are advantageous because they would allow data to be recorded by a suitable device and then the data generated by that suitable device analysed by the analyser. The acoustic input means may be linked to the processing means by a remote connection, or may comprise a remote connection. For example, the remote connection may be a wireless, or a wired connection. The remote connection may allow a real time (or substantially real time) or a recorded signal (any of which may be digital or analogue) to be fed to the processing means. Such a remote connection may be advantageous because it allows greater flexibility in use of the analyser; it may be easier to position the acoustic input means. Indeed, the remote connection may allow the patient to be in a different location to the processing circuitry. For example, the patient may be in his/her home and the processing circuitry may be in a hospital or the like. In perhaps the preferred embodiment the acoustic input means comprises an acoustic microphone which is preferably insulated with foam material to dampen unwanted interferences. The analyser may comprise a memory containing data corresponding to the blood flow through blood vessels. Conveniently, the processor may be arranged to compare the signal, or portions thereof, to the data held in the memory. In other embodiments the processor may be arranged to run an algorithm on the signal in order to determine whether the blood flow is occluded or partially occluded. It will be appreciated that a blood vessel (generally an artery) may have its cross section reduced by a number of factors which include stenosis (narrowing of the vessel) and the plaques described above. The effect of various types of reduction in cross section can have a different effect on the signal. The analyser may be arranged to determine between types of vessel cross section reduction. A blockage within a blood vessel will generally cause turbulent flow within the blood therein. The analyser may be arranged to analyse the turbulent flow in order to determine information about the blockage. In one embodiment the analyser is arranged to use the presence of the turbulent flow to determine the location of the blockage. Conveniently, the analyser is provided with a memory such that signals, or the processed signal can be stored therein. Such an arrangement is convenient since it will allow the signals to be reviewed or further analysed at a later time. The analyser may be provided with a linking means which allows it to be connected to another processing device, such as a PC, or the like. The linking means may comprise a serial (including Universal Serial Bus USM, Firewire ) connections, Bluetooth connection or a network (such as Ethernet or IEEE802.11 which is also known as WIFI, or the like) connection or the like. Further the analyser may be arranged to co-operate with a docking cradle. Preferably the analyser is arranged to receive power from a docking cradle to which it is connected and/or establish a data connection with a further device via a docking cradle in which it is placed. The parameter of the blood flow may comprise the percentage occlusion of the flow within the vessel; According to a second aspect of the invention there is provided a machine readable medium containing instructions arranged to cause a processor to function as the processor of the first aspect of the invention. According to a third aspect of the invention there is provided a program arranged to process data representative of a blood flow and determine whether the blood flow is occluded or partially occluded. In some embodiments the program may be arranged to compare the data with data stored in a memory. Such a comparison is convenient since it may be computationally efficient and yet provide accurate results. The program may be arranged to process the data according to an algorithm. According to a fourth aspect of the invention there is provided a method of analysing blood flow through a vessel comprising generating a signal corresponding to an acoustic signal generated by blood flowing through the vessel and processing the signal to determine properties about the blood flow in the vessel and generate an output indicative of one or more parameters of the blood flow. In one embodiment the method may be arranged to locate and/or quantify an occlusion with a blood vessel. In another embodiment the method may time the occurrence of features within the blood flow. Such a method is advantageous because it can allow problems with the heart to be diagnosed. In one embodiment the method uses the acoustic signal generated by turbulent flow in the blood vessel to locate the cause of the turbulent flow (for example a plaque). The method may comprise moving the analyser along the vessel to locate an acoustic signal which corresponds to the location of the occlusion. The method may provide a reading in real time; real time is intended to mean the display of the results as the method is being used. In the preferred embodiment the results are displayed substantially instantaneously but substantially real time is intended to include a delay between a reading being taken and the result being shown of up to roughly 2 or 3 minutes or any time in between. In alternative or additional embodiments the method may store the acoustic signal for later analysis. The method may record the signal as part of a medical record. The method may monitor the signal over a period of time to determine changes in the signal recorded at intervals of time. The interval of time may be a number of weeks, a number of months or even a number of years or decades. For example, it may be advantageous to monitor the amount of occlusion of a blood vessel over a time to see whether the occlusion is increasing in which case it may be desirable to prescribe a change in diet and/or lifestyle. Advantageously the method requires the patient to hold his/her breath as a reading is taken which is advantageous in order that the acoustic signal is not corrupted by breathing noise. Generally, the patient will only need to hold his/her breath for a few seconds. The machine readable medium of any of the above aspects of the invention may comprise any of the following non-exhaustive list: a floppy disk; a CDROM; a DVD ROM / RAM (including + R, + RW and -R, RW); a memory; a hard drive; any form of magneto optical storage; a transmitted signal (which may be an Internet download, ftp transfer or the like); a wire, bus or other data connection; or any storage medium. There now follows by way of example only a detailed description of embodiments of the invention with reference to the accompanying drawings of which: Figure 1 schematically shows an acoustic artery analyser adjacent a patient; Figure 2 schematically shows components of an acoustic artery analyser; Figure 3 shows an output of an embodiment of an acoustic artery analyser showing a plot at a predetermined frequency for an artery having 0% occlusion; Figure 4 shows a screen shot from an embodiment of an artery analyser showing the output format of Figure 3 but for an artery having 60% occlusion; Figure 5 shows an output of an embodiment of an acoustic analyser showing a variety of plots for an artery having 0% occlusion; Figure 6 shows the output format shown in Figure 5 but for an artery having 60% occlusion;Figure 7 shows an output of an embodiment of an acoustic artery analyser showing a 3D plot for an artery having 0% occlusion; Figure 8 shows the output format shown in Figure 7 but for an artery having a 60% occlusion; Figure 9 shows an output from an embodiment of an acoustic artery analyser which has been filterd so as to show the beats of a heart; Figures 10 to 15 show outputs from an embodiment of an acoustic artery analyser showing a number of heart conditions each of which has been filtered to remove extraneous noise; and Figure 16 shows a further embodiment of an analyser according to an embodiment of this invention. Although this invention has wider applicability it is convenient to describe its use in relation to monitoring the carotid artery to be found in the neck of a patient. The patient may be a human or animal and embodiments of the invention may be used on any blood vessel in the blood circulatory system. In a human there are two common carotid arteries, one on each side of the neck which divide into a right and left internal carotid arteries, and right and left external carotid arteries. The carotid arteries deliver oxygen-rich blood from the heart to the head and brain. Blockages or partial blockages can lead to strokes. Figure 1 shows an analyser 50 comprising a probe device 100 adjacent the neck 102 of a patient whose carotid artery 104 it is desired to monitor. The device 100 comprises an acoustic microphone 106 which provides an acoustic input means and provides a mechanism for generating a signal representative of the blood flow within the carotid artery 104, or other blood vessel. The microphone provides a passive transducer and therefore generates the signal according to the acoustic signal generated by the blood flowing through the vessel. The device 100 is connected to processing circuitry 108 via a remote wired connection 110. In other embodiments the connection may be made via a wireless connection such a radio connection, or the like, or the processing circuitry may be included within the device 100.Figure 2 shows the components of the device and of the processing circuitry 108 in more detail. The device 100 comprises a pre-amp 200 in order that the signal generated by the microphone 106 is more robust before it is transmitted down the connection 110. The processing circuitry 108 comprises an Analogue to Digital converter 202 arranged to transfer the signal into the digital domain. The digitised signal is passed to a DSP 204 (digital signal processor) in order that the signal is processed (in this embodiment an FFT is performed as described below). The DSP 204 passes its output to a processor 206 which communicates with a display 208 and a memory 210. In other embodiments transforms in addition to or alternatively to an FFT may be performed. It is however, the currently preferred method to use an FFT.Some of these alternatives, such as a Discrete Fourier Transform, may reduce the processing power required at the expense of accuracy. However, the reduced accuracy may be acceptable. In this embodiment the analyser 50 is portable and is thus powered by a battery 212. In other embodiments the analyser 50 may be powered from fixed supply such as the mains. The processing circuitry 108 may be provided by any suitable means and may be provided by a suitably programmed computer such as a laptop, PDA, desktop computer or the like. In other embodiments, the processing circuitry may be provided by numerous devices including processors, micro-controllers, ASIC's (Application Specific Integrated Circuit) or the like. Blood flow through the blood vessel, in this case the carotid artery, generates a sound. Occlusions within the vessel will generate turbulent flow which will modify the sound generated by the blood flow. The skilled person will appreciate that every complex sound is made up of a spectrum of discrete sinusoidal waves which may be harmonically related or may simply be a random collection and give a multidimensional spectrum. Sounds such as those caused by turbulence in the blood flow will have the added dimension of a measurable change in the spectrum of frequency components with time compared to those that would be generated in a blood vessel in which there is no occlusion. Blood flow has a periodic nature caused by the beat of the heart pumping the blood. Therefore, sounds generated by an occlusion will also have a periodic nature such that they will repeat and will be unique to the set of circumstances giving rise to the sound such as obstruction in the vessel. From this multi-dimensional spectrum a unique signature can be generated which will match with signatures previously sampled to provide a useful and simple diagnostic tool. The signature will be a representation of the shape of change and not of the individual frequencies, which make up that change. The processing circuitry 108 is in communication with a memory 210. It will be appreciated that for the processing circuitry 108 to be in communication with the memory 210, the memory 210 need not be within the analyser 50. The memory 210 may for example be connected to the processing circuitry 108 via a network connection. Further, the memory may be provided by a variety of different means. For example, the memory 210 may be provided by a random access memory (RAM) which may be volatile or non-volatile, a disk drive or the like. Reference to the memory 210 is intended to cover all of these possibilities. In the preferred embodiment the memory 210 is programmed with a plurality of signatures which have previously been sampled from blood flowing through the carotid artery 104 and as such provide a look up table but other means such as a database or the like may also be used. In operation, the probe device 100 is held adjacent the neck 102 of the patient in proximity to the carotid artery 104. The microphone 106 picks up sound produced by the blood flow in the carotid artery 104 and generates a signal which is passed to the processing circuitry. It will be appreciated that the sound produced by the blood flow will be periodic in nature due to the periodic nature of blood flow. The processing circuitry causes a sample of a predetermined length to be captured which is digitised for further processing. In the embodiment being described a sample of about 5 seconds is taken. However, it is perhaps desirable that the signal records the blood flow generated by at least two beats of the heart.For the avoidance of doubt the processing circuitry may be arranged to capture a sample of roughly any of the following lengths: 1 second, 1.6 seconds, 2 seconds, 3 seconds, 4 seconds, 6 seconds, 10 seconds or any time between these. In this embodiment the signal is digitised, by the AD converter 202 at a frequency of substantially 44.1kHz which is convenient since it is well used by sound processing software. The processing circuitry 108 (and in this example the DSP 204) then performs an FFT (Fast Fourier Transform) on the digitised signal in order to move the signal into the frequency domain. It will be appreciated that the sampling may be performed at other frequencies. The FFT generates a set of amplitudes for a plurality of predetermined frequencies within each sample of the digitised signal. Thus, a 2D plot (amplitude vs frequency) is generated for each sample. An example plot can be seen in Figure 3 for a healthy blood vessel having 0% occlusion. It will be seen that the highest frequency at which a signal is detected occurs at a point 300 which corresponds to a signal of roughly 5kHz. A similar plot is shown in Figure 4 for a blood vessel that has a 60% occlusion caused by a plaque therein. It will be seen that the highest frequency at which a signal is detected occurs at a point 400 which corresponds to a signal of roughly 11kHz. The increased frequency at which a frequency is detected is due to the turbulent flow caused by the plaque. Figures 5 and 6 each show 6 plots, each of which can be used to provide different information. The plot labelled '1' in Figure 5 and 6 provides a plot of the max. frequency along the time axis of Figure 7 and 8 respectively. The plot labelled '2' in each Figure 5 and 6 provides a plot of min. frequency along the time axis of Figure 7 and 8 respectively. The plot labelled '3' in Figure 5 and 6 shows the processing of the current signal (i.e. the leftmost line along the frequency axis of Figures 7 and 8 respectively). The plot labelled '4' in each of Figures 5 and 6 shows the lowest frequency vs. time which would generally allow the heart beat to be isolated although this cannot be seen in the examples of Figures 5 and 6. The plot labelled '5' shows the average frequency along the time axis of Figures 7 and 8 respectively.The plot labelled '6' in each of Figures 5 and 6 shows the percentage change in the frequency over time which may be used to infer the percentage occlusion. As each sample is processed further 2D plots are created and the processing circuitry may be arranged to generate a 3D plot using the subsequent samples to add a time dimension. Examples of such 3D plots are shown in Figures 7 and 8; Figure 7 shows a plot for a healthy blood vessel and Figure 8 shows a blood vessel with 60% occlusion. A screen display from an analyser according to one embodiment of the invention is shown in Figure 4. A series of check boxes 402 allows a user to select the desired output and the options shown in this embodiment are: EQ (Equaliser) mode (which is the view shown in Figures 5 and 6); spectrum (which provides a spectrum analysis); an oscilloscope (which is the view shown in Figure 4); a 3D display (which is the view shown in Figures 7 and 8); a filtered 3D display; and an area graph. Comparing Figures 7 and 8 it will be seen that the turbulent flow generated by the plaque in the artery causes higher frequencies to be generated in Figure 8 (corresponding to a blood vessel having a 60% occlusion). The 3D profile shown in Figures 7 and 8 may be advantageous in allowing an operator to interpret the blood flow within the vessel (carotid artery 104). An operator may be able to infer more from such a wave profile than may be inferred by the processor 204 in a comparison with a look up table. In order to reduce the processing requirement the processing circuitry is arranged to process every nth sample and average each sample in between rather than processing every sample. The degree of accuracy required for the later analysis may determine the proportion of the samples that are processed. In some embodiments the proportion of samples that are processed is variable. The wave profile shown in Figures 7 and 8 comprises a series of peaks with each peak corresponding to a frequency in the original signal. The height of a peak will relate to the strength (i.e. the volume) of that frequency in the signal. The strength (i.e. the volume) of a particular frequency within the signal will depend on the flow within the artery (i.e. whether there is an occlusion). Thus, the peaks generated in the wave profile will contain information about the occlusions within the artery.The device 100 may be used to locate plaques or other localised problems within the blood vessel (in this case the carotid artery 104). A user may move the device 100 along the body of the patient above the path of the blood vessel under investigation. The point of maximum amplitude of the peaks may be used to infer the location of the plaque or other problem within the blood vessel at the location of the device 100. Further, the processing circuitry is arranged to process only frequencies that have changed between one sample and the next; thereby taking what may be thought of as the first differential of the signal. Such use of only the information that has changed between samples is a technique that will be fully appreciated by the person skilled in the art. In this embodiment the amplitudes generated by the FFT are compared with the signatures which have previously been sampled which are held in a look-up table within the memory 210. In other embodiments the previous samples may be held in mechanisms other than a look-table such as a database, or the like. In the embodiment described above the analyser is larger, perhaps a desk top device or the like. It will be appreciated that providing a larger device will generally mean that greater processing power may be provided, the device may be powered from a fixed supply as opposed to a portable supply such as a battery, and other advantages. Further, the display 208 may be larger and capable of displaying more information such as the waveforms shown in Figures 3 to 8. In other embodiments the analyser 50 may be contained in a handheld device such as the example shown in Figure 16. The processing circuitry 108 is arranged to cause the display 208 to output the results of the comparison with the previous samples. In this embodiment the display is arranged to display as a percentage the amount of occlusion occurring in the Carotid artery 104. For example if there is no occlusion, that is in a healthy artery, the display will generate a reading of 0% (i.e. the processing circuitry 108 determines that the amplitudes generated by the FFT match the previous sample of a healthy artery with a 0% occlusion). If the artery were 75% blocked then the display would generate a reading of 75% (i.e. the processing circuitry 108 determines that the amplitudes generated by the FFT match the previous sample of an artery with a 75% occlusion).Such a display is convenient because is provides a readily understandable reading that will not generally require a skilled operator to understand. As such a device may be suitable for use in health centres, the offices of General Practioners (GP's), the home of a user, or the like and it may provide a screening device that alerts the user to the fact that there is a problem that should be investigated further. Because the device described in this embodiment relies on a look up table held in the memory it may be desirable to perform calibration on the device. The device may therefore be provided with a calibration mode in which it is held against a model or a healthy carotid artery (i.e. one in which there in known to be 0% occlusion) and the processing circuitry calibrated such that the output of the FFT corresponds to the profile of a healthy artery. In other embodiments the device may be arranged to detect blood flow in other blood vessels such as the aorta, other veins or arteries. Other embodiments of the invention may also be arranged to determine whether there are defects within the heart of the patient by timing the occurrence of predetermined features within the signal. In some embodiments the features correspond so specific frequencies generated by the occurrence of the systolic and diastolic pressure waves within the vessel. Figure 9 shows a 3D plot isolating these features. The feature corresponding to the systolic pressure wave is seen as a peak on the plot at 900 and the feature corresponding to the diastolic pressure wave is seen as a peak on the plot at 902. In order to produce the plot shown in Figure 9 a filter has been applied to remove any unwanted noise. The plot shown in Figure 10 shows a plot that would be recovered from a patient that has an aortic regurgitation (this occurs when the valve on the exit of the aorta does not function properly and blood flows back into the heart). It will be seen that the features 900 and 902 that were evident in Figure 9 have disappeared. Causes of aortic regurgitation include any of the following non-exhaustive list: valve disease, rheumatic fever, infective endocarditis, rheumatic arthritis, SLE, Marfan's disease, ankylosing spondylitis. It will be seen from Figure 10 that the peaks 900 and 902 which are shown in Figure 9 are decreased in amplitude and become continuous-there are no gaps between the peaks. The plot shown in Figure 11 shows a plot that would be recovered from a patient that has aortic stenosis which may occur due to calcification of the aortic valve. Signs of this condition include any of the following nonexhaustive list: slow rising pulse with narrow pulse pressure and ejection systolic murmur. It will be seen from Figure 11 that the magnitudes of the peaks 900 and 902 are reduced when compared to those of a normal heart shown in Figure 9. The plot shown in Figure 12 shows a plot that would be recovered from a patient that has mitral regurgitation which may be caused by any of the following non exhaustive list: ischaemic heart disease, papillary muscle dysfunction, mitral valve prolapse, endocarditis, rheumatic heart disease. As will be seen from Figure 12 amplitude of the peaks 900 and 902 is diminished and ripples 1200 may be produced at higher frequencies. The plot shown in Figure 13 shows a plot that would be recovered from a patient that has a VSD (ventral septal defect). VSD is caused by a hole in the septum-i.e. the barrier between the right and left ventricles. The peaks in the beat comprise 3 sub peaks 1300, 1302, 1304 rather than the two of a normal heart beat. There are also ripples 1306 at higher frequencies just past the position of the 3 peaks. The plot shown in Figure 14 shows a plot that would be recovered from a patient that has a atrial septal defect (ASD) which is a hole in the sepum separating the left atrium from the right atrium. It will be seen that the peaks 900 and 902 are reduced in amplitude. The plot shown in Figure 15 shows a plot that would be recovered from a patient that has a mitral stenosis the causes for which include any of the following non exhaustive list: rheumatic, congenital, prosthetic valve, malignant carcinoid, endocardial fibroelastosis. The more severe the stenosis the longer the diastolic murmur. This results in distinct large amplitude 1500 peaks with smaller peaks 1502 in between with some features at higher frequencies 1504. In any of the above embodiments, the system may comprise a recording device. For example, looking at the embodiment of Figure 1, the device 100 may comprise a recording device arranged to record the acoustic input received by the microphone 106. In such an embodiment, the recorded acoustic input could be transmitted via the connection 110 to the processing circuitry for analysis at a time later than the capture of the acoustic signal and in such an embodiment the acoustic input means may be provided by a means on the processing circuitry 108 for receiving the recorded signal. The recording of the acoustic input may be made in the digital or analogue domain. Although shown as a wired connection in Figure 1, the connection 110 may be wireless or by also comprise a Wide Area Network (WAN) connection such as the Internet or the like, a Local Area Network (LAN) connection. This would apply to the connection whether a real time (or substantially real time) signal or a recorded signal is being sent from the device 100 to the processing circuitry 108. When recording an acoustic input and/or transmitting it over a network (whether LAN or WAN) it may be convenient to store the recording in the digital domain. In such embodiments any of the following nonexhaustive lists of formats may be suitable: MP3, AIFF, WAV.

Claims (27)

1. An acoustic blood circulatory system analyser comprising an acoustic input means arranged to receive at least one of an acoustic input generated by blood flowing through a blood vessel and data representative of an acoustic input generated by blood flowing through a blood vessel and generate a signal therefrom, a processing circuitry arranged to receive and process the signal, the processing performed by the processing circuitry being arranged to analyse the blood flow through the vessel and generate an output from an output means of the analyser indicative of one or more parameters related to the blood flow.

2. An analyser according to claim 1 in which the processing circuitry is arranged, in use, to output a parameter indicating whether the blood flow within the vessel is occluded or at least partially occluded.

3. An analyser according to claim 2 in which the analyser is arranged, in use, to determine the cause of the occlusion of the blood vessel and can at least distinguish between stenosis and a plaque.

4. An analyser according to claim 3 in which the analyser is arranged, in use, to determine the location of a plaque within a blood vessel.

5. An analyser according to any preceding claim in which the processing circuitry is arranged, in use, to compare the signal with one or more previously stored signals in order to analyse the blood flow through the vessel.

6. An analyser according to claim 5 as it depends directly or indirectly from claim 2 in which the previously stored signals comprise a look-up table, database or the like and wherein the device is arranged such the comparison determines whether the blood flow within the vessel is occluded or at least partially occluded.

7. An analyser according to any preceding claim which is arranged, in use, to time the occurrence of one or more predetermined features of the signal.

8. An analyser according to claim 7 which is arranged, in use, to time the relative and/or the absolute times at which features corresponding to the pressure waves in the blood flow caused by the diastolic and the systolic contractions of the heart occur in the signal.

9. An analyser according to claim 7 or 8 which is arranged, in use, to use the time of the occurrence of the features to diagnose problems with the heart and the parameter is an indication of the problem.

10. An analyser according to claim 9 in which the analyser is arranged to diagnose one or more of the following: abnormal heart rhythms; conduction defects; heart valve defects.

11. An analyser according to any of claims 8 to 9 which is arranged, in use, to use the presence of one or both of the features corresponding to the systolic and diastolic pressure waves to determine the degree of occlusion of the vessel.

12. An analyser according to any of claims 7 to 11 in which the processing circuitry is arranged, in use, to compare the signal with one or more previously stored signals in order to analyse the blood flow through the vessel.

13. An analyser according to 12 as it depends directly or indirectly from claim 9 in which the previously stored signals comprise a look-up table, database or the like and wherein the device is arranged such the comparison provides the diagnosis.

14. An analyser according to any of the preceding claims in which the processing circuitry is arranged, in use, to perform at least one of the following on the signal in order to generate the output: Fast Fourier Transform; Discrete Fourier Transform; Laplace Transform; autocorrelation function.

15. An analyser according to any preceding claim in which the processing circuitry is arranged, in use, to generate a spatial frequency profile from the signal.

16. An analyser according to any preceding claim in which the processing circuitry is arranged, in use, to generate a table of frequencies and/or amplitudes from the signal.

17. An analyser according to any preceding claim in which the device is arranged, in use, such that the reception of the signal by the signal processor is synchronised with an external event.

18. An analyser according to claim 17 in which the external event is the heart beat.

19. An analyser according to any preceding claim in which the acoustic input means comprises a microphone, or other sound transducer.

20. An analyser according to any of claims 1 to 18 in which the acoustic input means comprises an analogue recording device arranged to record an analogue signal.

21. An analyser according to any of claims 1 to 18 in which the acoustic input means comprises a digital input means arranged to receive digital data representative of an acoustic input generated by blood flowing through a blood vessel.

22. An analyser according to any preceding claim in which the acoustic input means is linked to the processing means by a remote connection.

23. An analyser according to any preceding claim which comprises a memory such that signals, or the processed signal can be stored therein.

24. An analyser according to any preceding claim which comprises a linking means allowing it to be connected to another processing device.

25. A machine readable medium containing instructions arranged to cause a processor to function as the processor of the first aspect of the invention.

26. A program arranged to process data representative of a blood flow and determine whether the blood flow is occluded or partially occluded.

27. An analyser substantially as described and as illustrated herein with reference to the accompanying drawings.