The physician must choose a stethoscope that fits the ears comfortably with the right angulation, has as short a segment of flexible tubing as possible, and is equipped with a diaphragm and a bell. Selection of the proper earpieces for comfort and the best transmission of sound is based on individual preference and is best evaluated by trial and error. A snug, comfortable fit depends on the size of the earpieces as well as the angle at which they enter the ear canal; the angulation of the rigid metal tubing therefore must be chosen to suit the comfort of the individual. The rubber tubing should be as short as feasible; experience indicates that tubing about 12 in (30 cm) long is the best compromise. Rapaport and Sprague213 have shown that thick-walled tubing about 3 mm in diameter is best suited to transmit sounds and murmurs.
The human ear is most sensitive to auditory vibrations that occur in the frequency range between 1000 and 4000 to 5000 Hz; the sensitivity falls off sharply when the frequency of vibration is below 1000 Hz. This is particularly true of low-frequency sounds, which must be of considerably greater amplitude to reach the threshold of audibility than sounds of higher frequency. Most cardiovascular sounds and murmurs of diagnostic importance are between 30 and 1000 Hz, thereby placing the auscultator at considerable disadvantage.214 Therefore, a stethoscope requires both a diaphragm and a belli, and each must be applied to the chest wall with optimal pressure. The diaphragm, which is fairly rigid, brings out the high frequencies and attenuates the lows. When the diaphragm is used to accentuate high-pitched sounds, it should be pressed very firmly against the skin. This technique will make a high-frequency murmur, such as the faint diastolic blowing murmur of aortic valve regurgitation, audible along the left sternal border when it would otherwise be missed. The bell tends to accentuate the low-frequency sounds and to filter out the high-pitched tones. Often, low-frequency sounds are more easily appreciated by palpation than by auscultation; in these situations, the stethoscope should be placed very lightly on the skin, with just enough pressure to seal the edge at the point of maximal impulse. With very light pressure of the bell, the low-pitched sounds are accentuated; however, with firm pressure of the bell against the skin, the skin itself becomes a relatively tight diaphragm, and the low-frequency sounds are suppressed. Although this technique can be very helpful, the stethoscope always should be equipped with a valve system that permits one to switch from the diaphragm to the bell with ease.
The examination should take place in a quiet room that is well lighted and comfortably heated. The patient should be properly gowned, with adequate exposure to the waist. The examining table should be large enough that the patient can be instructed to lie flat, sit up, or roll to one side with complete ease. Usually, the physician will examine from the right side, and it is equally important that the physician be comfortable.
Prior to auscultation, the clinician should take advantage of the information obtained from the history as well as from the examination of the arterial, venous, and cardiac pulsations. When abnormalities are found, their auscultatory counterparts should be pursued diligently. For example, prominent a waves in the jugular venous pulse should alert the clinician to search carefully for a low-pitched, right-sided fourth heart sound (S4) or the subtle presystolic murmur of tricuspid stenosis, whereas large v waves that augment with inspiration should suggest tricuspid regurgitation. The presence of pulsus alternans always should demand a careful search for third and fourth heart sounds (S3, S4), as well as for the presence of functional mitral or tricuspid regurgitation, often present in severe cardiac decompensation. A rapid, jerky rise of the carotid pulse may be the clue to the diagnosis of hypertrophic cardiomyopathy, which can be confirmed by manipulating the systolic murmur with maneuvers that change the pre- and afterloading conditions of the heart.
There are four primary areas of cardiac auscultation: (1) the primary and secondary aortic areas in the second right interspace and the third left interspace adjacent to the sternum, respectively, (2) the pulmonary area in the second left interspace, (3) the tricuspid area in the fourth and fifth interspaces adjacent to the left sternal border, and (4) the mitral area at the cardiac apex. This does not mean to imply that auscultatory events arising from each valve are heard only in their respective areas. The murmur of aortic stenosis in the elderly is often heard best (and at times only) at the apex, whereas the murmur of a flail posterior mitral leaflet may radiate to the base and simulate the murmur of aortic stenosis. Ejection sounds arising from the stenotic aortic valve are usually most prominent at the apex, whereas the opening snap of mitral stenosis is heard best midway between the tricuspid and mitral areas. The murmur of tricuspid regurgitation may be appreciated best at the classic mitral area if the right ventricle occupies the apex. Furthermore, cardiac auscultation should not be restricted to just these four areas. For example, the murmur of aortic regurgitation secondary to abnormalities of the aortic root may be heard best to the right of the sternum, whereas the murmur of tricuspid regurgitation in the emphysematous patient with pulmonary hypertension may be heard best in the epigastrium. The continuous murmur of a patent ductus arteriosus is heard just below the left clavicle, whereas the murmur of large bronchial collaterals may be most prominent in the posterior thorax. Again, the overall clinical presentation will guide one to the appropriate area to auscultate.
During auscultation, one listens both specifically and selectively for heart sounds and then for murmurs, first during systole and then during diastole. As described by Levine and Harvey,215 the physician should adopt a systematic approach to listening. The patient should be lying on his or her back, and each area should be surveyed with both chest pieces. In each area examined, the physician listens specifically for the first heart sound (S1), noting its intensity, constancy, presence of splitting, and variation with respiration. This is followed by selective listening for the second heart sound (S2), noting the same characteristics. Then extra sounds are searched for and carefully listened to, first in systole and then in diastole, with mental notations as to their time of appearance, pitch, and other characteristics that may identify them as gallop sounds, ejection sounds, or valve-opening sounds. Whether the examination is initiated at the base by listening to S2 or at the apex by listening to S1 depends on the physician's preference. Of greater importance is that the examination be performed in a methodical, systematic way, with the physician listening intently for one event at a time. Attention is then first turned to systole and then to diastole for the presence of murmurs. After this general survey, the physician listens selectively for certain sounds and murmurs. With the bell applied lightly to the skin at the apex, the patient is instructed to roll onto the left side, and the clinician selectively "tunes in" to diastole and the low-frequency range. This allows the physician to determine the presence or absence of diastolic filling sounds or diastolic rumbles arising from the AV valves. The examination is continued with the patient in the sitting position. While the patient leans slightly forward during quiet respiration, the clinician can optimally appreciate splitting of S2. With the patient's breath held in deep expiration, the physician examines the aortic and pulmonic areas with the diaphragm firmly pressed against the chest wall, selectively "tuning in" to the high-frequency range in an effort to hear the faint blowing diastolic murmur of aortic regurgitation or, if the clinical situation warrants, the presence of a pericardial friction rub. Sounds and murmurs such as these are discovered only when they are searched out carefully with intent listening and concentration.
Auscultation of the heart should be considered a dynamic exercise. In addition to being auscultated in the left lateral ducubitus position, the patient should, when possible, also be examined while standing, squatting, and during the Valsalva maneuver and following its release. This type of dynamic examination changes the pre- and afterloading conditions of the heart and may yield diagnostic information because of the typical response of heart sounds and murmurs to these maneuvers.
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