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Rouanet, more than 140 years ago, attributed the second heart sound to closure of the aortic and pulmonic valves. When the second sound is split and both components can be heard and identified, a reliable judgment about the relative loudness (intensity) of each component can be made. The Valsalva maneuver may also be used to exaggerate splitting of the second sound. The supine position in young patients, for example, may yield an erroneous impression of abnormally wide S 2 splitting, which can be avoided by reexamining the patient in the sitting or standing position. As with the first sound, the patient should be examined in several positions. The patient's age must be taken into consideration when assessing splitting of the second sound, since the likelihood of hearing a single S 2 during both respiratory phases increases with advancing age. The interval between the two audible components of the second heart sound normally increases on inspiration and virtually disappears on expiration. Slow, regular respirations are best for auscultation because a long deep breath may attentuate P 2 by interposing lung tissue over the stethoscope, and only a single sound will be heard. The examiner will wish to note respiratory variation both during quiet breathing and at times during exaggerated breathing. The influence of respiration on the second sound is extremely important. In order to appreciate splitting of S 2, it may be useful to gradually move the stethoscope ("inching") from the second right ICS to the fourth left ICS. Splitting is best identified in the second or third left ICS, since the softer P 2 normally is confined to that area, whereas the louder A 2 is heard over the entire precordium, including the apex. It is clinically very important to determine the presence and degree of respiratory splitting and the relative intensities of A 2 and P 2. It has two audible components, the aortic closure sound (A 2) and the pulmonic closure sound (P 2), which must be separated by more than 20 msec (0.20 sec) in order to be differentiated and heard as two distinct sounds. The second heart sound is of shorter duration and higher frequency than the first heart sound. When listening to the heart sounds, it is essential simultaneously to palpate either the carotid artery or apex impulse to determine the onset of systole. The second sound, like the first, is evaluated by sequentially auscultating over the second left ICS, the fourth left ICS along the left sternal border, and the cardiac apex. Then begin cardiac auscultation with the stethoscope placed at the second right ICS. Clinical assessment of S 2 is best performed with the patient lying comfortably in the supine position and breathing normally.įirst, attempt to palpate the aortic and pulmonic components of the second heart sound in the second right and second or third left intercostal spaces (ICS), respectively. The examination should be performed in a warm, quiet room in a manner identical to that described in Chapter 22, The First Heart Sound.