Surgery – Truss – Pad
Patent
1996-03-05
1997-11-11
Kamm, William E.
Surgery
Truss
Pad
A61B 502
Patent
active
056853173
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an apparatus for measuring the function of a person's heart valve, the apparatus being of the kind which uses an acoustic signal from the person's cardiac function measured at the outside surface of the body.
When physicians listen to heart sounds by means of a stethoscope they listen, for example, for those sounds which are generated by the blood flowing from the heart into the aorta. Such sounds are caused by turbulence in the flow after passage of a heart valve, and the character of such a sound gives a good background for evaluating the properties of the heart. It has been shown to be desirable to be able to classify persons, with or without circulatory problems, into several groups, some of which contain persons who will have to be subjected to more thorough diagnosis. The classification alone requires vast experience on the part of the physician and becomes expensive to perform. Hence there is a need for a measuring apparatus which is capable of performing this classification.
The connection between heart sound measured on the outside of the body and those conditions of a heart which cause the heart sound is well known and is used by trained physicians based on experience with the stethoscope sound in the physician's ear. It has been recognized that certain forms of apparatus and signal processing may support the physician in his interpretation of the heart sound, and procedures are known in which sonograms are displayed on a screen or are printed out. Thus the interpreting by the physician is moved from being an auditory problem to being a visual problem in which characteristic patterns have to be recognized visually. Furthermore, with sonograms there is more time for analysis, since the analysis is no longer tied a function in real time.
It has, however, turned out that the known techniques are too time consuming to be useful in other than purely experimental measuring situations, since the spectrum analysis that is used is dependent on integration over many heartbeats, because there are many outer influences on the measured signals and furthermore inter-cycle differences. The known techniques hence do not allow ordinary clinical use and are still dependent on learning complex pattern recognition.
SUMMARY OF THE INVENTION
It is a purpose of the invention to provide an apparatus which is simple to use and which gives a large certainty for correct identification of the heart valve function. This is provided in the present invention by an apparatus which comprises a measuring microphone with a preamplifier, a preemphasis filter for compensating for the degree of obesity of the person, a spectrum analyzer which determines the relative energy distribution in at least one lower and at least one higher frequency range, where those parts of the acoustic signal which are to be analyzed are synchronized by means of a signal which is derived from electrocardiographic signals from the person, with or without a time delay.
It has been recognized in the invention that only through cooperation between a number of techniques for signal extraction and noise reduction, both for acoustic noise and electric and electromagnetic noise, is it possible to provide an apparatus which functions without the need for human intervention to reject irrelevant information.
In a preferred embodiment, in order to extract without time delay a synchronizing signal from the electrocardiographic signals, a non-recursive predictor for noise signals of the electrical mains frequency and its harmonics is used, and the noise signals are subtracted from the amplified electrocardiographic signal, followed by detection based on pattern recognition of the temporal placement of the QRS complex in the electrocardiograph signal that has thus been cleaned of noise.
Stethoscopes as well as microphones or accelerometers placed on the chest collect signals which have been filtered by tissue, in particular fatty tissue, which is interspersed between the sound source, in this case the heart, and the
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Bang & Olufsen Technology A/S
Evanisko George R.
Kamm William E.
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