Under what conditions do innocent or functional murmurs generally disappear and increase?

Innocent or functional murmurs are typically related to the dynamics of blood flow and the physiological variations that occur with different positions or activities. The correct answer emphasizes that these murmurs often disappear when a person is standing or straining due to the fact that these actions can change the hemodynamics and decrease blood flow through the cardiac structures, thus reducing the turbulence that causes the murmur. Conversely, these murmurs can increase with increased cardiac output, which occurs during situations such as exercise or stress, where blood flow is augmented, leading to enhanced turbulence and potentially more pronounced sounds.

Understanding this pattern is vital in differentiating innocent murmurs from pathological ones, especially in younger patients or athletes. These murmurs are not anomalies but rather reflect normal physiological changes. The other options do not accurately describe the behavior of functional murmurs under varying conditions. By focusing on the relationship between body position, exertion, and blood flow dynamics, one can gain insight into how and why innocent murmurs may vary in intensity or become inaudible.