Why Is Diastole Essential in the Cardiac Cycle?
A diastole or diastolic function of the heart is the process where the heart muscles go through relaxation which is followed by the filling of blood in the heart's chambers. This as a result decreases the blood pressure of an individual. Thus, diastole heart function is a phase in the cardiac cycle of a person which is responsible for ventricular relaxation along with the active and passive filling of blood in the heart chambers before pumping them out throughout the body.
This is a very important topic for understanding the cardiac cycle of humans and how an abnormal diastolic function can result in several heart diseases.
This article provides information on ventricular diastole and left ventricular diastolic dysfunction definition. Students can also refer to this article to understand diastolic dysfunction meaning.
Definition of Diastole and Systole
Before understanding the cardiac cycle and knowing the abnormalities of heart functioning, it is important to get a clear understanding of the diastole and systole.
Ventricular diastole and systole form a major part of the cardiac cycle. These can be defined as the two periods in a cardiac cycle which occurs in the form of heartbeats. They pump the blood through the blood vessels which is carried to each and every part of the body.
Diastole is the relaxation of the ventricles and pumping of blood into the heart chambers while systole can be defined as the contraction of heart muscles to pump out blood in the entire body.
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Ventricular Diastolic Dysfunction
The trouble in relaxation of heart muscles and reduction in the pumping of blood into the ventricles of the heart is known as ventricular diastolic dysfunction.
Left ventricular diastolic dysfunction (DD) is characterized as the ventricle's failure to fill to a normal end-diastolic volume, both during exercise and at rest, while left atrial pressure does not surpass 12 mm Hg.
The occurrence of mild diastolic dysfunction starts with slow heartbeats due to the limited amount of blood flow in the ventricles required for the next heartbeat.
A normal left ventricular diastole requires proper relaxation, contraction and ejaculation of blood throughout the body for normal functioning of the heart.
The two common main reasons for left ventricular diastole dysfunction are:
Due to an Overworked Heart Muscle: This is caused by the high amount of physical activity which as a result thickens the muscles of the heart creating less space inside the heart ventricles for filling in blood.
Clogged Arteries: Muscle bulking and stiffening of heart muscles can be genetic but the most common factors for these has always been a high level of cholesterol and blood pressure. Clogging of heart arteries results in narrowed heart valves which block several proteins, irons and other substances to filtrate out of the arteries making the heart stiffer.
Causes and Effects of Diastolic Heart Failure
Several factors contribute to abnormal functioning of the heart. Some of the main factors include ageing, aortic stenosis, pericardial diseases and hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy is the abnormal thickening of the left ventricular wall while aortic stenosis can be defined as the narrowing of the aortic valve opening.
These abnormalities lead to the accumulation of fluids in the pericardial space causing a sudden heart failure.
Other factors for diastolic dysfunction include diabetes, high blood pressure, obesity and coronary heart diseases.
Symptoms of Diastolic Heart Failure
Although people show no diastolic dysfunction symptoms, many may experience issues with breathing difficulty, fatigue and irregular heartbeat. They also face difficulty in doing physical activities and have a lack of appetite. Many severe symptoms include abdominal swelling, rapid weight gain and swelling of the ankle and legs (edema).
Many people also face severe chest pain and foamy, pink mucous after coughing. Therefore it is important to do a regular checkup of your heart and maintain a low cholesterol level for better functioning of the heart.
FAQs on Understanding Diastole: Meaning, Phases & Importance
1. What is diastole in the context of the human cardiac cycle?
Diastole is the specific phase of the cardiac cycle when the heart muscle relaxes after a contraction. During this period, the chambers of the heart—the atria and ventricles—are able to fill with blood, preparing for the next heartbeat. It is the resting period essential for proper heart function.
2. What is the main difference between systole and diastole?
The primary difference lies in the heart muscle's action and the direction of blood flow.
- Systole is the contraction phase, where the ventricles pump blood out of the heart into the aorta and pulmonary artery.
- Diastole is the relaxation phase, where the heart chambers fill with blood.
3. What happens to the heart chambers and blood flow during ventricular diastole?
During ventricular diastole, the ventricular muscles relax, causing the internal pressure to drop significantly. This triggers the semilunar valves (aortic and pulmonary) to close, preventing backflow from the arteries. Simultaneously, the lower pressure causes the atrioventricular (AV) valves (tricuspid and mitral) to open, allowing blood to flow passively from the atria into the ventricles, filling them up for the next contraction.
4. What is 'joint diastole' and why is it significant in the cardiac cycle?
Joint diastole is the specific period within the cardiac cycle when all four chambers of the heart are simultaneously in a relaxed state. It occurs after ventricular systole and before the next atrial systole. Its importance is immense because it allows for the passive filling of the ventricles with approximately 70-80% of the blood from the atria, which is crucial for maintaining an efficient cardiac output without the atria having to contract forcefully every time.
5. How does diastolic pressure reflect a person's overall cardiovascular health?
Diastolic pressure measures the pressure in the arteries when the heart is at rest between beats. A healthy diastolic reading indicates that the blood vessels are elastic and can accommodate blood flow with minimal resistance. A consistently high diastolic pressure suggests that the arteries may be stiff or narrowed, meaning the heart and blood vessels are under strain even during the relaxation phase. This is a key indicator of hypertension and an increased risk of heart disease and stroke.
6. Which heart valves are open and which are closed during ventricular diastole?
During ventricular diastole, the heart is focused on filling the ventricles. Therefore:
- The Atrioventricular (AV) valves (the tricuspid on the right side and the mitral on the left side) are OPEN to allow blood to flow from the atria into the ventricles.
- The Semilunar (SL) valves (the pulmonary and aortic valves) are CLOSED to prevent blood that was just pumped into the arteries from flowing back into the relaxing ventricles.
7. Why is the relaxation phase (diastole) just as critical as the contraction phase (systole)?
The diastolic phase is critical because it is the only time the heart's main pumping chambers, the ventricles, can fill with blood. Without an adequate diastolic period, the ventricles would not receive enough blood. This would mean that during the next systole, a smaller volume of blood (reduced stroke volume) would be pumped to the body and lungs. Furthermore, the heart's own coronary arteries receive most of their blood flow during diastole, making it essential for the heart muscle's own oxygen supply.
8. Can a problem in the diastolic phase affect the systolic phase?
Absolutely. If the ventricles cannot relax properly during diastole (a condition known as diastolic dysfunction), they cannot fill effectively. This directly limits the amount of blood available to be pumped out during the subsequent systole. Even if the heart's contraction (systolic function) is perfectly healthy, the cardiac output will be low because the starting volume was insufficient. This demonstrates the deep interdependence of the two phases for efficient heart function.
