What causes the high aortic pressure during mid-diastole?

The high aortic pressure during mid-diastole is primarily attributed to the passive filling of the ventricles. During diastole, the heart is in a relaxed state, allowing blood to flow from the atria into the ventricles. This passive filling occurs when the atrioventricular (AV) valves are open, and blood flows under pressure from the atria into the ventricles.

The aortic pressure is high at this point because the aorta's elastic walls have distended due to the ejected blood during the previous ventricular contraction (systole). As the heart relaxes and fills with blood, the aortic pressure remains relatively elevated; this is essential for maintaining perfusion pressure throughout the body. The passive flow increases venous return, which contributes to this sustained pressure in the aorta.

Atrial contraction and ventricular contraction are processes that occur at different times in the cardiac cycle and significantly impact the pressure dynamics in the aorta, but they do not directly explain the high pressures observed specifically during mid-diastole. Similarly, blood volume increase does influence overall pressures but does not specifically account for the aortic pressure during this distinct phase of the cardiac cycle.