Base Left: Physiological Splitting of the Second Sound (S2)
A physiological split occurs when both components of the second sound are separately distinguishable. Normally, this split sound is heard on inspiration and becomes single on expiration. The A2 and P2 components of the physiological split are about .03 seconds apart.The physiological split is heard during inspiration because it is during that respiratory cycle that intrathoracic pressure drops. This drop permits more blood to return to the right heart. The increased blood volume in the right ventricle results in a delayed pulmonic valva closure. At the same time, the capacity of the pulmonary vessels in the lung is increased which results in a slight decrease in the blood volume returning to the left heart. With less blood in the left ventricle, its ejection takes less time resulting in earlier closing of the aortic valve.
The net effect, therefore, of inspiration, is to cause aortic closure to occur earlier and pulmonary closure to occur later. Thus, a split sewcond is heard during inspiration and a single second sound is heard during expiration.
The sound you heard represents a normal individual with physiological splitting of the second sound.