Let's now turn to the last very important area of bedside diagnosis, that is, auscultation. There are traditionally four areas in which we listen: apical (or mitral area), lower left sternal edge (or tricuspid area), upper left sternal edge (or pulmonary area), upper right sternal edge (or aortic area). Of course, one sometimes listens into the neck and in other areas where murmurs or sounds may radiate.
It's very important to know how to utilize the stethoscope as well. Note the tubes on the stethoscope are short, so that you are close to the patient and really appreciate the sounds. Remember, high frequency sounds with the diaphragm, the more low frequency sounds with the bell and, in fact, one little technique you should learn is you can always press on the bell, tightening and stiffening up the skin, stretching it and making the skin into a diaphragm - so the bell really becomes a critically important instrument for you.
Now we are going to listen for the first sound which announces systole, the second sound which announces the end of systole, and we're going to think about blood flow and the pressure curves, because at the bedside, with auscultation and the other disciplines we've gone through, we can really appreciate the physiology of the patient with the skills we are learning.
Remember, lub dub, lub dub, lub dub - it tells us systole is beginning, systole is ending. These techniques will tell you about the contraction of the heart, its relaxation and the physiology of the patient.
Foci
Auscultation is usually begun at the aortic area. The stethoscope is then sequentially moved to the pulmonary, tricuspid and mitral areas. Keep in mind that murmurs may radiate widely, and that they may be present in areas other than the classic ones described.
Inching the stethoscope across the chest is a useful technique to define the area where a given acoustic event is best heard. For best results one should selectively tune in on the individual sounds and murmurs that may be present.
Pressure curves
It is most important to keep in mind the events of the cardiac cycle when interpreting the acoustic events at the bedside.
These simultaneous left atrial, aortic and left ventricular pressure curves illustrate the relationship of these hemodynamic events to the genesis of the heart sounds.
Analogous events of the cardiac cycle occur in the right heart, but at a lower pressure.
Left ventricular systole begins with the first heart sound, or s1, it occurs when the pressure in the left ventricle rises above that of the left atrium closing the mitral valve. This sound occurs just before the carotid impulse and is loudest at the apex.
As left ventricular pressure continues to rise above aortic pressure, the aortic valve opens. Normally, no sound is produced by valve opening.
Systole ends and diastole begins with the second heart sound, or s2. It occurs when left ventricular pressure falls below that of the aortic root, closing the aortic valve. This sound occurs at the end of the carotid impulse and is loudest at the base.
As left ventricular pressure falls below left atrial pressure, the mitral valve opens, a normally inaudible event.
Volume curves
Blood flow is greatest in early systole and early diastole. Approximately two-thirds of the blood ejected leaves the ventricle in the first one-third of systole, and two-thirds of the blood filling the ventricle enters during the first one-third of diastole. This information is useful when analyzing the significance of certain auscultatory events.