![]() The exact cause of the sound is unclear, but a normal S3 occurs as a brief, low-frequency vibration. S 3 is associated with the rapid filling phase of the ventricle (when the AV valves open), about 0.14 to 0.16 seconds after S2 (closure of the aortic and pulmonic valves). Table 5.1: Changes in S2 splitting and possible underlying causes. Pulmonary hypertension with equal ventricular pressures.Large ventricular septal defect (equal ventricular pressures).One semilunar valve is absent (e.g., truncus arteriosus, valvular atresia).RV outflow obstruction (e.g., pulmonary stenosis).Right ventricle (RV) volume overload (e.g., atrial septal defect).This physiological splitting can be heard with a stethoscope, but can be further influenced by diseases as listed in table 5.1.įigure 5.2: Normal splitting of S2 with inspiration. Conversely, during inspiration pulmonary artery pressure falls, so pulmonic valve closing occurs later and A2 and P2 occur further apart (figure 5.2). In expiration pulmonary artery pressure is higher, so the pulmonic valve closes earlier and P2 occurs closer to A2. How split A2 and P2 are depend on physiological conditions, primarily the phase of breathing that influences the pulmonary artery pressure. As aortic pressure (80 mmHg) is far greater than pulmonary artery pressure (10 mmHg), S2 is normally split with two components (A2 and P2) relating to the closure of the aortic and pulmonic valves, respectively. S2 is caused by closure of the aortic and pulmonic valves at the beginning of isovolumetric ventricular relaxation when ventricular pressure falls below pulmonary and aortic pressure. Conversely, in the case of a left bundle branch block, the normal splitting of S1 may be absent (figure 5.1) as M1 is delayed and so occurs in synchrony with T1.įigure 5.1: Normal and abnormal differences in the components of S1 (M1 and T1). The reasons for M1 preceding T1 are not clear, but may be due to the force generation of the left ventricle being slightly faster than that of the right ventricle. The splitting of S1 can be more pronounced and audible in the presence of a right bundle branch block (figure 5.1) that causes left ventricular contraction (and mitral valve closure) to markedly precede contraction of the right ventricle. The mitral valve normally closes slightly (0.04 seconds) before the tricuspid, causing S1 to be "split" (i.e., actually being two sounds, M1 and T1 (figure 5.1)), but the time gap is too short with a normal heart to be detectable with a stethoscope. The ventricle is beginning to contract, so ventricular pressure quickly rises above atrial pressure and the atrioventricular (tricuspid and mitral) valves close, producing the S1 sound. S1 occurs at the beginning of isovolumetric contraction. The first and second sounds (S1 and S2) are the fundamental heart sounds.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |