And what can we learn from the acoustic events at the lower left sternal edge using the bell of the stethoscope? Let us listen together and analyze. Again, the carotid vessel is your timing mechanism and watch respiration. Everybody listen together. [Cut-away]
Well, we certainly learned a lot by watching respiration and listening carefully with the bell at the lower left sternal edge. When this patient breathed in, we heard [sounds], breathed out [sounds]. That is, those low frequency sounds, the third and fourth heart sounds, were heard in inspiration because they are generated from the right side. As you inspire, you augment right heart flow and these filling sounds, therefore, are heard better in inspiration.
Oscilloscope
By viewing an oscilloscopic image and simultaneously listening, we can further appreciate these auscultatory events.
S4
Fourth heart sounds are presystolic filling sounds related to atrial systole. Because the are low in frequency, the bell of the stethoscope helps to differentiate the S4-S1 combination from a split S1. They are best heard at the tricuspid and mitral areas in patients with decreased right and left ventricular compliance respectively. When right sided, they may augment with inspiration.
S3
Third heart sounds are early diastolic, low frequency sounds best heard with the bell of the stethoscope. The occur approximately fifteen hundredths of a second afer the second sound and are related to the acceleration and deceleration of blood during early passive filling of the ventricle. Left ventricular left sounds may be normal, or physiologic, in children and young adults as blood rapidly decelerates into the ventricle. They may also be pathologic in heart failures, as blood rapidly decelerates due to a stiff non-compliant ventricle. Left ventricular left sounds are best heard at the apex. Right ventricular third sounds are best heard at the tricuspid area and may augment with inspiration.