From the Research
No, the second heart sound (S2) is not diastole itself but rather marks the beginning of diastole. S2 occurs when the aortic and pulmonic valves close at the end of systole, creating a characteristic "dub" sound that can be heard during auscultation. This valve closure happens as the ventricles finish contracting and begin to relax, signaling the transition from systole to diastole. After S2, the ventricles continue to relax and fill with blood during the diastolic phase of the cardiac cycle. Understanding this distinction is important for clinical assessment, as abnormalities in the second heart sound (such as splitting or accentuation) can provide valuable diagnostic information about cardiac function and potential pathologies affecting the semilunar valves or the pressure dynamics between the ventricles and great vessels.
The provided evidence does not directly address the question of the second heart sound and its relation to diastole. However, it discusses various aspects of cardiovascular diseases and their management, including the use of beta-blockers and ACE inhibitors 1, pulmonary hypertension 2, antihypertensive therapy in patients with aortic stenosis 3, and the role of ACE inhibitors, ARBs, and beta-blockers in treating hypertension 4. None of these studies directly relate to the definition or timing of the second heart sound in the cardiac cycle.
It's also worth noting that the study from 1984 5 is unrelated to the question at hand, as it discusses the measurement of gingival crevicular fluid and does not provide any information relevant to cardiac physiology or the second heart sound.
In clinical practice, accurately identifying and interpreting heart sounds, including the second heart sound, is crucial for diagnosing and managing cardiovascular conditions. The second heart sound is a critical landmark in the cardiac cycle, marking the end of systole and the beginning of diastole, and its characteristics can provide important clues about cardiac function and potential pathology.