During expiration, the positive intrathoracic pressure causes decreased blood return to the right side of the heart. This is defined as physiologic splitting of S 2. This causes an increased delay in the P 2 component of S 2 relative to the A 2 component. The increased blood volume in the right ventricle causes the pulmonary valve to stay open longer during ventricular systole. The S 2 sound results from reverberation within the blood associated with the sudden block of flow reversal.ĭuring inspiration, negative intrathoracic pressure causes increased blood return into the right side of the heart, yet some slowing of emptying from the left side. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary (outlet) valve closes. As the left ventricle empties, its pressure falls below the pressure in the aorta, aortic blood flow quickly reverses back toward the left ventricle, catching the aortic valve leaflets and is stopped by aortic (outlet) valve closure. The second heart tone, or S 2, is caused by the sudden block of reversing blood flow due to closure of the aortic valve and pulmonary valve at the end of ventricular systole, i.e beginning of ventricular diastole. Second heart tone S 2 the "dub"(components A 2 and P 2) The S 1 sound results from reverberation within the blood associated with the sudden block of flow reversal by the valves. When the pressure in the ventricles rises above the pressure in the atria, venous blood flow entering the ventricles is pushed back toward the atria, catching the valve leaflets, closing the inlet valves and preventing regurgitation of blood from the ventricles back into the atria. The first heart tone, or S 1, is caused by the sudden block of reverse blood flow due to closure of the atrioventricular valves, mitral and tricuspid, at the beginning of ventricular contraction, or systole. Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur.įirst heart tone S 1, the "lub"(components M 1 and T 1) Valve insufficiency (or regurgitation) allows backflow of blood when the incompetent valve is supposed to be closed. Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, causing turbulence as blood flows through it. Murmurs may be physiological (benign) or pathological (abnormal). Heart murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs and adventitious sounds. These are the first heart sound (S 1) and second heart sound (S 2), produced by the closure of the AV valves and semilunar valves respectively. In healthy adults, there are two normal heart sounds often described as a lub and a dub (or dup), that occur in sequence with each heart beat. In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which provide important information about the condition of the heart. The heart sounds are the noises ( sound) generated by the beating heart and the resultant flow of blood through it. Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. Risk calculators and risk factors for Heart soundsĮditor-In-Chief: C. US National Guidelines Clearinghouse on Heart soundsĭirections to Hospitals Treating Heart sounds Ongoing Trials on Heart sounds at Clinical Ĭlinical Trials on Heart sounds at Google Ventricular septum.Īrticles on Heart sounds in N Eng J Med, Lancet, BMJ Second heart sound caused by semilunar valves - Aortic (A) and Pulmonary/Pulmonic (P).Ī picture showing the location of the heart valves and which sound they create Diagram showing relations of opened heart to front of thoracic wall. Heart valves are labeled with "B", "T", "A", and "P".įirst heart sound: caused by atrioventricular valves - Bicuspid/Mitral (B) and Tricuspid (T). Front of thorax, showing surface relations of bones, lungs (purple), pleura (blue), and heart (red outline).
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