Procedure for extracting information from a heart sound signal
AssigneeBang & Olufsen Medicom A/S
InventorFlemming Munk
Life of this patent
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Abstract
A procedure for extracting features from phonocardiographic signals without the use of synchronizing information from electrocardiographic signals. The features extracted are the timing and value of first and second heart sounds and various combinations of timing and value of signal components constituting heart murmur. Such combinations are directly related to various heart conditions, which are more easily diagnosable by a medically trained person when assisted by the signal extraction. The features are extracted by a novel combination of energy/time relationships for the heart signal and various novel classification schemes.
Claims4
A procedure used for extracting murmur information, characterised in that it comprises the following steps:
- obtaining a digital representation of heart sound for a predetermined number of seconds,
- identifying the time of occurrence of the first and second heart sounds in each cycle,
- windowing the parts of heart sounds falling between the first and second heart sounds, and second and first heart sounds, respectively
- decomposition of the signals into a predetermined first number n1 of frequency bands, each band being decomposed into a predetermined second number n2 of time-slices
- obtaining a systole (SP) and a diastole (DP) power vector consisting of the sum of n1 powers measured in each of the n2 time slices
- for each combination of a frequency band and a time slice, the power values from the different systoles are compared, and the median value is chosen to be the standard value for a power vector
- obtaining a systole (SMF) and a diastole (DMF) mean frequency vector by weighting the power value for each of n1 frequency bands with the mean frequency of the corresponding band, summing the results and dividing the sum by the corresponding element in the respective systole or diastole power vector
- while using the time of occurrence of the intensity vectors of the various classes for classifying the time distribution of murmurs.
An apparatus for performing the procedure of extracting information from a phonocardiographic signals obtained from a transducer and subjected to signal processing including identification of characteristic signal components, comprising the steps of:
- detecting first and second heart sounds and placing them correctly on a time axis by performing the steps of:
- extracting the first and second heart sounds by classification according to energy levels,
- then performing instantaneous power and lowpass filtering of the original phonocardiographic signal by performing spectral analysis and feature enhancement to obtain the energy content present in areas of a time-frequency representation delimited by frequency band time intervals in the form of energy distributions,
- classifying the energy distributions according to pre-defined criteria,
- comparing the energy distributions to a catalogue of distributions related to known medical conditions, and
- outputting values for any medical conditions found;
- wherein signal processing means are used to produce a spatial sound distribution based on frequency, a low frequency band being delivered to a first earpiece of a headphone and a high frequency band being delivered to a second earpiece of said headphone, the frequency bands containing first and second heart sounds and murmur sounds respectively;
- and wherein said signal processing means comprise at least one Wiener filter.
Dependencies are inferred from the claim text.