Diastole

Diastole is the part of the cardiac cycle when the heart relaxes and fills with blood. This occurs between contractions (systole), specifically between the second and first heart sounds. It is the longest phase of the cardiac cycle and includes both early diastole, when the ventricles first relax and start to fill; and late diastole, when the ventricles complete filling with blood from the atria.

Phases of Diastole

Diastole is divided into four phases: isovolumetric relaxation, rapid filling, diastasis, and atrial contraction.

Isovolumetric Relaxation

This is the initial phase of diastole. During this phase, the ventricles begin to relax and the pressure within the ventricles drops. The aortic valve and pulmonary valve close to prevent the backflow of blood into the ventricles. The mitral valve and tricuspid valve are also closed at this time, so no blood is entering the ventricles, hence the term "isovolumetric".

Rapid Filling

In the rapid filling phase, the pressure in the atria becomes higher than the pressure in the ventricles. This causes the mitral and tricuspid valves to open, allowing blood to flow into the ventricles. This phase is called "rapid filling" because it is the phase where the ventricles fill the fastest.

Diastasis

Diastasis is a slower filling phase that occurs before the atria contract. During this phase, blood continues to flow into the ventricles, but at a slower rate.

Atrial Contraction

The final phase of diastole is atrial contraction. During this phase, the atria contract, pushing the remaining blood into the ventricles. This phase is also known as "atrial kick" because it provides the final push of blood to fill the ventricles before the next contraction.

Clinical Significance

Abnormalities in diastole can lead to diastolic heart failure, where the heart is unable to fill properly. This can result in symptoms such as shortness of breath, fatigue, and edema. Diastolic dysfunction can be caused by conditions such as hypertension, coronary artery disease, and aging.

See Also

• Systole
• Cardiac cycle
• Heart sounds
• Heart failure

References

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