Content Writer-SME
The contraction and relaxation of the heart are associated with systole and diastole, which form one cardiac cycle. The flow of blood is initiated from the region of high blood pressure to the region of low blood pressure. Systole and diastole ensure that blood is continuously and uniformly circulated throughout the body.
What is Systole and Diastole?
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Systole and diastole are related to the contraction and relaxation of heart muscles and together they forms a cardiac cycle. Both these conditions are measured with the help of an instrument called sphygmomanometer along with a stethoscope.
- The first sound the doctor hears when using a stethoscope to measure BP is called a "lub" and the second sound is called a "dup".
- These lub and dup sounds are called systole and diastole in medical language.
- Health professionals monitor systole and diastole pressure to check whether the person is suffering from hypertension or hypotension.
- The normal value of blood pressure in a healthy adult is 120/80 mm Hg (where mm of Hg represents the pressure of mercury).
Systole and Diastole
Systole Meaning
Systole refers to the phase of a cardiac cycle during which the heart is in a contracting state. During this step, the cardiac muscle pushes out the blood from the heart. After that, blood flows to the rest of the tissues and organs of our body.
- The first wave, the P-wave on ECG represents the contraction of atria which is called atrial systole.
- In order to ensure effective blood circulation throughout the body, systole is a vital phase of the cardiac cycle.
- At rest, systole usually lasts 0.3 seconds, which is less than diastole in a normal cardiac cycle.
- Conditions like heart failure may be indicated by systolic abnormalities, such as a decreased ejection fraction.
Diastole Meaning
Diastole refers to the stage of cardiac muscles, which involves the relaxation of ventricles. This phase involves the filling of blood in the chambers of the heart. The moment the heart stops beating and is filled with new blood, blood pressure decreases.
- The relaxation of the ventricles occurs during ventricular diastole, and the relaxation of the atria occurs during atrial diastole.
- Usually lasting longer than systole, diastole allows enough time for the heart to fill with blood.
- Heart failure with intact ejection fraction is a condition that results in the heart not being able to relax properly.
Systole Vs Diastole
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Systole and diastole are related to each other which can be best understood with the help of the major differences explained in detail below:
| Parameters | Systole | Diastole |
|---|---|---|
| Definition | The contracting state of human heart is called systole. | The relaxed state of human heart is called diastole. |
| Measurement | The top value of the blood pressure represents systole or systolic pressure. | The bottom value of the blood pressure represents diastole or diastolic pressure. |
| What happens during this time? | The ventricles of the heart contract and push blood towards the pulmonary trunk. | During the diastolic state, the heart muscles relax and the chambers of the heart fill with blood. |
| Value | The normal value of systolic blood pressure in a healthy adult is 120 mm of Hg. | The normal value of diasystolic blood pressure in a healthy adult is 80 mm of Hg. |
| Valves | During this period all the valves remain closed. | All valves open again during diastole. |
What is a Cardiac Cycle?
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The series of events that occur between one heartbeat and the next heartbeat is called a cardiac cycle. This starts with the relaxed state of the atrium and ventricle. The cardiac cycle is controlled by electrical signals coming from the “atrioventricular (AV)” and “sinoatrial (SA)” nodes. Atrial Systole, Ventricular Systole, Atrial Diastole, and Ventricular Diastole are the four phases of the cardiac cycle.
Atrial Systole
Atrial Systole is a phase during which atrial chambers are in a depolarized state. This is marked by contraction of the atrium which is followed by the rise in pressure inside the atria. During atrial systole, the blood flows from the atrium to the ventricle via the atrioventricular valve.
Ventricular Systole
The contraction of the ventricles is followed by a rapid increase in the pressure that results in the closure of all valves. Due to this, the flow of blood is blocked temporarily. Ventricular systole is also called isovolumetric phase, in which the volume of blood remains constant.
Atrial Diastole
Heart chambers become relaxed during atrial diastole phase. This results in the opening of the atrioventricular valves, closing the pulmonary artery and aortic valve.
Ventricular Diastole
Ventricular diastole is the state in which ventricles enter into the relaxed state. Furthermore, a gradual decrease in pressure is also observed during this phase. The duration of each phase of the cardiac cycle is as follows:
| Events | Duration |
|---|---|
| Atrial Systole | 0.1 s |
| Ventricular Systole | 0.3 s |
| Atrial Diastole | 0.7 s |
| Ventricular Diastole | 0.5 s |
Systolic and Diastolic Blood Pressure
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Two types of blood pressure that regulate the activity of a cardiac cycle are systolic and diastolic pressure:
Systolic Blood Pressure
During systolic blood pressure, blood is released into arteries during the heart's beat, or systole.
- The blood is dynamically ejected into the arteries, which raises the blood pressure of an individual.
- This pressure is attained during a strong contraction of the heart.
- The normal range of systolic blood pressure in a healthy human is 120mm of Hg.
Diastolic Blood Pressure
The process of ventricular relaxation is called diastole. The blood pressure measured during diastole is known as diastolic blood pressure.
- During this phase, pressure is exerted by blood vessels in the arteries between heartbeats.
- The cardiac ventricles immediately relax after a heart contraction, and the blood is refilled during this phase.
- The normal range of diastolic blood pressure is 80mm of Hg.
- In cases of hypertension, the blood pressure of an individual rises frequently.
Things to Remember
- The overall systolic and diastolic activities of the heart are measured by an electrocardiogram (ECG).
- A single cardiac cycle consists of four major steps: Atrial Systole, Ventricular Systole, Atrial Diastole, and Ventricular Diastole.
- The duration of atrial systole ranges from 0.3 to 0.4 seconds in one cardiac cycle.
- A gradual increase and decrease in pressure occurs throughout the cardiac cycle.
- Individuals with high systolic BP have a higher risk of cardiovascular diseases than those with high diastolic BP.
- Hypertension and hypotension are the two medical conditions that are determined by the values of systole and diastole.
Sample Questions
Ques. What is hypertension? (2 marks)
Ans. The condition is called hypertension when the systolic blood pressure exceeds 140 mm of Hg, and the diastolic blood pressure is above 90 mm of Hg.
- In this case, a patient has a high possibility of getting strokes, diabetes, and other severe diseases.
- The disease is usually seen in adults or individuals with a family history.
Ques. What is the duration of one complete cardiac cycle? (2 marks)
Ans. There are 72 cardiac cycles in a minute when a heart that is functioning properly beats 72 times per minute. The duration of one cardiac cycle is about 0.8 seconds.
Ques. Why does diastolic blood pressure increase beyond the normal range? (2 marks)
Ans. Smoking and high alcohol consumption raise the risk of diastolic high blood pressure. Apart from this, stress, high salt, and low sodium in the diet may also contribute to diastolic hypertension.
Ques. What do you understand about double circulation? (2 marks)
Ans. Double circulation refers to the situation where blood passes through the heart twice in one cycle.
- There are two paths where blood travels in double circulation: pulmonary circulation and systemic circulation.
- In birds and animals, double circulation.is observed.
Ques. What are the warning signs of diastolic dysfunction? (2 marks)
Ans. The improper functioning of lower heart chambers (ventricles) results in a condition called diastolic dysfunction. The warning signs and symptoms are:
- Fatigue
- Difficulty in breathing
- Swelling
- Irregular heartbeat
Ques. What are atria? (2 marks)
Ans. Atria are the upper heart chambers that pass the received blood from veins to ventricles. The right atrium and the left atrium together constitute the atria.
Ques. What are the lub and dub sounds of the heart? (2 marks)
Ans. The first sound of the heart heard in the stethoscope is called lub.
- This is marked by the closure of tricuspid and bicuspid valves.
- Dub is the second sound of the heart which is linked with the closure of semilunar valves.
Ques. Which is more important, high systolic BP or diastolic BP? (2 marks)
Ans. In individuals with hypertension, the possibility of coronary heart disease, left ventricular hypertrophy, chest pain, renal failure, and death is determined by high systolic blood pressure at age 50 rather than diastolic readings. Thus, high systolic BP is more dangerous and should be cured in early stages by adopting healthy eating habits.
Ques. What are the differences between systole and diastole? (3 marks)
Ans. The differences between systole and diastole are as follows:
| Systole | Diastole |
|---|---|
| The contraction of the heart muscles is called systole. | The relaxation of the heart muscles is called diastole. |
| The normal range of systolic blood pressure is 120 mm of Hg. | The normal range of diastolic blood pressure is 80 mm of Hg. |
| During this phase, all the valves are closed. | Diastole is marked by the opening of valves. |
Ques. What is a sphygmomanometer? (2 marks)
Ans. An instrument that monitors the blood pressure is called a sphygmomanometer. The blood pressure is displayed in the ratio of systolic BP/ Diastolic BP. The normal range of blood pressure in a healthy human is 120mm of Hg / 80mm of Hg.
Ques. What do you understand about the joint diastole? (2 marks)
Ans. The situation in which all the chambers of the heart are in a relaxed state is called joint diastole. During this stage, blood flows from veins into the corresponding auricles, and the pressure inside the ventricles drops until it becomes less than the pressure inside the arteries.
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