What is Windkessel effect? Cardiology Basics

What is Windkessel effect? Cardiology Basics

The term ‘Windkessel effect’ is used in the setting of large elastic arteries like aorta. Elastic arteries  have elastic tissue much more than the muscular arteries and are located nearer to the heart. Elasticity helps these blood vessels to maintain a relatively constant pressure gradient and flow though, the heart is pumping only intermittently.

The original term ‘Windkessel’ means ‘air chamber’ in German language. It was an air chamber used in fire engines in the 18th century, to maintain continuous delivery of water for fire-fighting. In the case of aorta, the aortic elasticity causes expansion and temporary storage of blood in systole so that more blood enters the aorta than what leaves it in systole.

This buffer stock of blood is released during diastole, to maintain blood flow to the organs while the heart is relaxing after a contraction. The Windkessel effect makes aorta function as a ‘second pump’ in diastole. This diastolic flow is quite important in the case of coronary arteries as coronary blood flow occurs mostly in diastole. Windkessel effect may be reduced in the elderly with stiff aorta due to arteriosclerosis. Reduced elasticity of the aorta in the elderly may also lead to elevation of systolic blood pressure without elevation of diastolic blood pressure.

The branches of coronary arteries entering the myocardium are compressed when the heart contracts in systole. So very little blood can enter the myocardium in systole. That is why the flow into the myocardium occurs predominantly in diastole when the heart relaxes. Windkessel effect in the aorta ensures that an adequate flow into the myocardium is possible even though heart is not pumping in diastole. Diastolic coronary flow is most important for the subendocardial regions which receive least blood in systole.