Aortic Regurgitation (AR) involves a malfunction of the aortic valve, which controls blood flow out of the left ventricle. Blood pressure is measured as systolic pressure (during a heartbeat) and diastolic pressure (between beats). In AR, while systolic pressure may be normal or elevated, the diastolic pressure often drops significantly lower than expected. This lowering is a direct consequence of the structural failure and the resulting backward flow of blood.
Defining Diastolic Pressure and Its Maintenance
Diastolic pressure (DP) represents the lowest pressure exerted on the arterial walls during the cardiac cycle. This pressure is measured during diastole, when the heart’s ventricles are relaxed and refilling with blood. During this resting period, arterial pressure is maintained by two primary physiological mechanisms.
The first is the elastic recoil of the large arteries, particularly the aorta, which acts as a pressure reservoir. After the left ventricle ejects blood, the stretched aortic walls recoil inward, continuously pushing blood forward into the circulation. The second is the resistance provided by the small arteries and arterioles, known as Systemic Vascular Resistance, which slows blood outflow and maintains a sustained pressure gradient.
A third element is the integrity of the aortic valve itself. The valve’s leaflets must close completely at the beginning of diastole, sealing the high-pressure arterial system from the low-pressure left ventricle. This closed valve traps blood volume in the arteries, allowing elastic recoil and peripheral resistance to maintain diastolic pressure. This sustained pressure ensures constant blood flow to the body’s tissues.
The Structural Failure in Aortic Regurgitation
Aortic Regurgitation is a condition where the aortic valve fails to close tightly. The valve normally consists of three delicate leaflets that should meet perfectly to form a seal after the heart ejects blood. When this coaptation fails, a structural defect, such as thickened or damaged leaflets, allows a gap to remain in the seal.
This structural failure creates a backflow pathway from the high-pressure aorta into the low-pressure left ventricle. This leak occurs during the diastolic phase of the cardiac cycle, precisely when the valve should be closed. Causes range from congenital defects, like a bicuspid aortic valve, to acquired issues such as infection or dilation of the aortic root.
The volume of blood that leaks backward is termed the regurgitant volume. This backward flow happens during ventricular relaxation, interfering with the normal pressure maintenance mechanisms. The severity of the structural failure dictates the volume of blood that escapes the arterial system with each beat.
The Physiological Impact on Arterial Pressure
Aortic regurgitation lowers diastolic pressure due to the rapid “diastolic runoff” caused by the incompetent valve. During diastole, aortic pressure is normally sustained by trapped blood volume and elastic recoil. With AR, the leaky valve provides a low-resistance escape route for blood back into the left ventricle.
Instead of pressure gradually declining forward, a significant volume of blood is rapidly siphoned backward. This abrupt volume loss prevents the elastic recoil from maintaining pressure. The pressure gradient drives this backward flow, causing the aortic pressure to decay much faster than normal.
The rapid pressure drop results in an abnormally low diastolic pressure measurement. This low reading, combined with a potentially high systolic pressure (due to the heart compensating by ejecting a larger volume), creates a widened pulse pressure. This wide difference is a characteristic sign of significant AR and reflects volume instability during the heart’s resting phase. The degree to which the diastolic pressure falls is directly related to the severity of the valve’s failure.