Contents
Phonocardiography refers to a type of diagnostic procedures aimed at determining the functioning of the heart muscle. It has been used in official medicine for a long time, so the method is considered obsolete. Today, he is rarely involved, usually in cases where it is a question of using phonocardiography by itself. If the patient was sent to do a classic electrocardiogram, then the technique often comes as a set for the main examination, which can significantly expand the information content of the results obtained.
During its activity, the heart makes many sounds that a person cannot hear in ordinary life. Special sensors help to do this, which pick up sounds during myocardial contraction, valve movement, and blood flow. The method of registering all internal sounds in medical terminology is briefly called FKG.
General facts
Initially, only a phonendoscope was used to assess the sound effects emanating from heart contractions. This way of listening is properly called auscultation. But it was far from always such a simple means to catch all the waves, which prompted specialists to create more advanced equipment aimed at capturing sounds.
After sound research methods gained acceptance, the inventors of medical devices tried to collect their useful properties to capture sounds under a common denominator. This is how percussion and some other branches of diagnostics appeared. But all of them could not absolutely guarantee the correctness of the assumptions of the attending doctor. The problem lay in the fact that with classical auscultation, each doctor hears his patient differently due to the characteristics of personal hearing and perception.
Also, the human ear is not able to catch a clear amplitude, the intervals between weak sound vibrations and their exact duration without amplifying devices. So the idea came up to make an independent apparatus that would take measurements completely objectively, relying only on science.
The basis for the improvements was the involvement of the device, where a special microphone was pre-installed. All incoming information was almost instantly transformed into a completely understandable graphic record. An experienced diagnostician or a narrow specialist working in the field of cardiology will be able to decipher it.
Initially, the methodology for assessing the health of the cardiovascular system was aimed at tracking down the location of each type of noise. A little later, experts learned to directly associate it with the contraction of certain parts of the heart, which made it possible to diagnose various pathologies more accurately.
One of the most important advantages of the survey is the ability to use it with equal effectiveness in both adults and children. There are also models of devices that are adjusted to the standards of the structure of the body of animals. They are installed in veterinary clinics.
Despite all the efforts of technicians, FCG did not become the main and only research option, after which it would be possible to accurately determine the diagnosis. Even experienced doctors still insist on undergoing other examinations, clinical tests, or studying the structure of large vessels through computed tomography with contrast.
Also, problems are added by the fact that only the master who is well versed in auscultatory signs should be engaged in decoding. Care must be taken to ensure that the sensors are laid according to strict regulations. And for this, one cannot do without the skills of handling a phonendoscope.
The essence of the technique
Human physiology provides for the formation of various sound waves, which have their own distinctive features. Sometimes it is difficult to distinguish them even for a professional. But it’s much easier to deal with the strength of sound characteristics and frequency.
Force is a value that is proportional to the amplitude of the generated wave. It is measured in decibels. The louder the final sound is, the greater the force with amplitude is displayed in the graphical result.
The frequency of the studied pulses is measured in Hertz. The value is the number of sound vibrations for a particular unit of time. The human ear can detect a range of 20 Hz to 20 Hz. Everything that is outside the allowable interval can be captured, converted into graphic information only with the help of special equipment.
A healthy heart muscle, together with all the accompanying actions, is capable of making noise at approximately 150 Hz to 200 Hz, which is enough to hear it with a phonendoscope. The noise product parameters are 1000 Hz.
But since most of the people who come to see a cardiologist are sick, it will not be possible to recognize their pathologies that respond with low-frequency vibrations without special equipment. Difficulties are added by the fact that of the main tone lines, the doctor will hear on his own only the first two in the most successful scenario.
Against the background of other sound options, it is difficult to recognize the third and fourth heart sounds. They are most often the basis for confirming suspicions of various diseases.
Schematically, all fixed sounds are divided into two types:
- tons;
- noises.
The first is a fairly loud, distinct and clear sound. In pathologies, in addition to tone, various noises become audible. They are not connected with each other, and also have different strengths, frequencies.
Most of the noise, along with tones, can be detected even simply by using auscultation with a phonendoscope. At the same time, their volume will change at different points. But if the patient hears from the medical staff in the diagnostic room something like: “Prepare the PCG,” this indicates the doctor’s suspicion of rare or complex anomalies. They can be both congenital and acquired.
Thanks to the phonocardiograph, it is possible to capture even minor noise effects, which are then converted into electrical signals in order to appear on paper in the form of specific graphs. The principle of operation is very similar to that of a traditional ECG.
The advantage of the phonocardiograph is the presence of many filters that are aimed at eliminating minor noises that do not carry any practical benefit for diagnosis. So it turns out to collect only the most accurate basic data for the result.
Due to the fact that the manipulation is non-invasive, it does not cause significant discomfort, painless. For this, she is loved by cardiologists who work with young children and even newborn babies.
For the procedure, special preparation of the patient, such as a special long-term diet, is not required.
Advantages and disadvantages
In addition to the absence of pain during manipulation, it has several other significant advantages. This is about objectivity, especially in situations where you need to correctly measure the intervals between a tone and the noise that follows it.
To do this, during preparation, you just need to properly fix the sensors, choosing the optimal point of contact.
But against the background of advantages, the method has several disadvantages. Not always the device captures absolutely all vibrations. This is explained by the fact that the device simply does not perceive some sounds. Sometimes it misses important low frequency vibrations that are not within its audible range. This means that they cannot be found on the final graph, but a specialist with a phonendoscope will hear them perfectly.
To avoid such an imbalance, the nurse should write down in conclusion not only the results of the FCG itself, but also the initial examination by the doctor. Here confusion is possible, so doctors have established an unspoken rule for themselves. If the vibrations are not heard through a phonendoscope, but are visible on phonocardiography, then preference is given to what the doctor heard himself. The only exception is recording at low frequencies. From this it follows that without preliminary auscultation, the examination is meaningless.
Another snag is the definition of timbre, which is also not within the competence of the machine. Instead, the duty specialist deals with the issue. At the same time, the timbre still remains a subjective characteristic, sometimes the device may not detect a number of valvular defects.
To obtain the most informative result, you must first listen to the patient’s chest in order to identify the individual best points for auscultation. A preliminary assessment of audibility is an important preparatory measure due to the fact that with the development of diseases, the heart tends to change:
- configuration;
- dimensions;
- boundaries.
If you rely on standards without reference to a particular patient, then the wrong position of the microphone leads to a decrease in sound strength.
Due to its safety, as well as the absence of a radioactive load, PCG has recently been used to confirm or refute fetal hypoxia.
Standard Readings
Phonocardiography is not a widely used diagnostic tool like ECG. It is prescribed only strictly based on the accompanying indications, and the final decision is made by the attending doctor. The main reasons for issuing a referral to the FCG are:
- rhythm disturbances;
- vices;
- cardiomyopathy.
The ability to dynamically monitor reproducible effects is highly valued by cardiologists and internists alike. Sometimes a rheumatologist becomes the author of the direction.
It is believed that the examination apparatus is available in many public hospitals or in almost every medical center. But in practice, it turns out that not all private clinics are ready to purchase equipment, which is increasingly called outdated. And in polyclinics, devices are written off without receiving new ones in return.
In order to obtain more reliable data, FCG is best done in the morning after a person has had a good night’s sleep. It is not necessary to refuse breakfast, but drinking tea, coffee, alcohol is not recommended. The reason for this is the high chances of provoking tachycardia or other rhythm disturbances.
At the very beginning of the procedure, the subject is laid on the couch, and then periodically asked:
- hold your breath;
- take a deep breath.
During the manipulation, the microphone is moved in different parts of the chest, using the information obtained from the auscultatory picture for the canvas. In rare cases, pharmacological preparations are additionally involved, designed to:
- dilate blood vessels;
- influence the rhythm.
If the drug load is not provided for by the prescription, then the reception takes about 10 minutes. If you need to bring drugs, the examination takes about half an hour. It is also worth considering the factor of whether phonocardiography is a procedure in its pure form, or it is combined with an ECG for increased clarity of the results.
Deciphering the norm
A healthy muscle allows you to clearly hear the first and second tones without unnecessary devices.
The first tone is formed when the valves, which are localized between the ventricles and atria, close. Closing the flaps makes a fairly loud sound, which has the following distinctive features:
- average frequency;
- amplitude – 25 mm;
- duration – 0,15 seconds.
It is not possible to cover the sounds from each individual valve due to the speed of the physiological reaction. Therefore, it is much more productive to try to catch at once all the vibrations inherent in the slamming of the valves, which are superimposed on each other, creating a single whole – the first tone.
The second tone covers the closure parameters of the aortic valves along with the pulmonary artery. It will be better to hear it if you move the microphone to the second intercostal space. We are talking about the right and left sides, respectively, because it is these points that most closely correspond to the optimal listening points for these anatomical structures.
Unlike the predecessor tone, in this case there is immediately a duet of components that come from each valve. It will be possible to distinguish sounds both simply with the ear and with the apparatus. It is easiest to listen to them from the following people:
- children;
- adolescents;
- skinny people.
The first sound captures the closure of the aortic valve. It is much louder than its analogue, and its amplitude sometimes exceeds the valve sound from the pulmonary artery by about two times. Anatomically, this phenomenon is explained by the fact that the pressure in the aorta is an order of magnitude higher.
Difficulties arise when registering with the help of FKG the third and fourth tones. But their detection does not always indicate the presence of pathology.
The third tone is sometimes heard in thin people, as well as babies. It is collected on the basis of fluctuations in the walls of the ventricles. It is also closely associated with physical activity, manifesting itself after activity. It is problematic to listen to it just like that, so it is recommended to record in the low-frequency range.
The fourth tone makes itself felt even less frequently than the third. But if it has already manifested itself, then this is more likely to indicate the presence of the disease.
Characteristics of pathologies
Starting to study the test results handed out, people far from medicine are lost. The configuration of the systolic shunt murmur tells them nothing, and any remarks about changing the size of the amplitude lead to panic.
The last aspect really suggests that the victim is likely to develop pathology, but here you need to consider each parameter in detail. If there was a weakening of the sound, which is recorded in the column “decrease in the intensity of the first tone”, then usually the deviation indicates:
- mitral valve insufficiency;
- stenosis;
- decrease in the contractile function of the left ventricle.
In the first option, the patient will face a change in the valve leaflets, which is a consequence of the inflammatory process or atherosclerosis. The desired sound wave is not fixed due to the incomplete slamming of the valve.
A specific stenosis is capable of blocking the complete closure of the hole, which is characterized by additional deposition of calcium salts. This development leads to shortening of the mitral valve leaflets.
A decrease in contractile capacity traditionally signals:
- cardiomyopathy;
- chronic ischemia;
- myocarditis, more often rheumatic type.
The expert also takes into account factors that lead to a similar sound result, but have a mediocre relation to cardiac activity. This is about:
- emphysema;
- obesity;
- some types of pleurisy;
- the pericardium.
Tones can not only weaken, but also intensify. The classical primary sources of changes are called thyrotoxicosis, anemia, mitral stenosis. But with stenosis of both valves, the first tone splits into a couple of subtones. The same can be traced with the blockade of the legs of the bundle of His.
The second tone can also be modified. Thus, an increase in amplitude can be traced in arterial or pulmonary hypertension. A similar clinical picture describes the thickening of the aortic valvular leaflets during the development of syphilis.
But sometimes this is quite normal if other tests do not confirm anything, and the patient himself is asthenic (thin). But even in such people, a weakening of the second tone can be found, which indicates insufficiency of the aortic valve and a decrease in blood flow through the pulmonary artery.
Things are a little more confusing with the third and fourth tones. Their deviations will tell about a much larger list of possible pathologies, among which are hypertension, myocardial infarction, cardiosclerosis with concomitant heart failure.
When the third and fourth tones are out of balance, they create a gallop rhythm. This is the first alarming bell, suggesting an impending heart attack, myocarditis, pronounced hypertension.
But no matter how detailed the diagnostic result is, it is imperative to take note of the results of other examinations. Based on the collected material, together with the patient’s current complaints, the doctor will be able to more accurately determine the diagnosis.