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The Cardiac Cycle

The Cardiac Cycle

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Introduction to the Cardiac Cycle

The cardiac cycle is the coordinated sequence of events that combine to produce a single heart beat. It consists of alternating stages of contraction and relaxation, where blood is pumped from the heart to the lungs and other organs of the body. This is highly important for the functioning of the human body as it ensures that oxygenated blood and nutrients reach all organs in order for them to remain healthy. Understanding the complex chain of occurances during the cardiac cycle is essential for medical professionals to diagnose and treat any irregularities or diseases affecting the heart.

The cardiac cycle consists of two main stages: atrial systole and ventricular systole. Atrial systole is the contraction of the atria, filling the ventricles with blood. Ventricular systole is the contraction of the ventricles, pushing the blood out to the lungs and other organs of the body. This process is known as diastole, where the heart relaxes and fills with blood to prepare for the next heartbeat. In order for this cycle to be regulated correctly several other components are involved, such as the great vessels, valves, and Wiggers' diagram.

Structure of the Heart

The heart is an organ composed of several main components, namely the great vessels, atria, ventricles, and valves. The great vessels are the veins and arteries that transport blood in and out of the heart. The atria are the two top chambers of the heart; they collect and contract to push blood into the ventricles. The ventricles are the two bottom chambers of the heart; they pump and contract to push blood into the vessels. Finally, the valves are the structures between the different chambers of the heart; the three main ones are the tricuspid valve, the aortic valve, and the pulmonary valve. These valves ensure that the blood flows in one direction; they open and close due to pressure changes within the heart.

The Cardiac Cycle

The cardiac cycle is the sequence of events that occur as the heart beats. It includes atrial systole, ventricular systole, and diastole. Each of these stages involves the contraction and relaxation of the heart muscle in order to pump blood into the various vessels of the body. This is the foundation of providing oxygenated blood to the vital organs of the body.

Atrial Systole

Atrial systole is the first stage of the cardiac cycle. The atria, the upper chambers of the heart, contract first, pushing blood into the ventricles. This is followed by ventricular systole, where the ventricles, or lower chambers of the heart, contract to pump blood out into the circulatory system. During diastole, the ventricles relax and fill with blood so that they can contract again in the next cycle.

The cardiac cycle of the heart can be represented visually with a Wiggers' diagram. This diagram is based on a principle known as ventricular pressure volume loops, and shows how changes in pressure and volume occur during different phases of the cardiac cycle. It illustrates the pressure-volume relationships inside the chambers of the heart during each phase, including atrial systole, ventricular systole, and diastole.

The diagram includes four quadrants which represent the four stages of the cardiac cycle. The horizontal axis is labelled volume and shows the amount of blood flowing from the atria to the ventricles during atrial systole. The vertical axis is labelled pressure and shows the corresponding pressure in the ventricles during ventricular systole. The dashed lines show the pressures in the atria during atrial systole, and the dashed vertical line shows the equilibrium point where pressure and volume are equal.

From the Wiggers diagram, it is possible to observe the changes in pressure and volume during the four stages of the cardiac cycle. During atrial systole, there is an increase in pressure and volume as atrial contraction forces blood into the ventricles. During ventricular systole, the pressure continues to increase until the pressure-volume loop reaches its maximum. Finally, during diastole, the pressure decreases as the ventricles relax before the next heart beat.

The Wiggers diagram is an important tool for understanding the cardiac cycle. It helps us to visualize the varying pressures and volumes during each stage of the cycle and enables us to better comprehend the overall process.

Cardiac Volumes

The amount of blood that is contained in the left and right ventricles are referred to as cardiac volumes. In a healthy heart, the amount of blood that is present in the heart continuously changes during the cardiac cycle. During the systole period, there is an increased pressure inside the left and right ventricles which pushes most of the blood out into the aorta and pulmonary artery. This is known as the end-systolic volume (ESV). When the pressure inside the heart returns to its normal resting state, the heart relaxes and fills again with the same amount of blood. This is known as the end-diastolic volume (EDV).

The difference between ESV and EDV is known as stroke volume (SV). SV is the amount of blood that the heart pumps out during one heart beat. Stroke volume can be calculated by subtracting the ESV from EDV. A normal adult has a stroke volume of approximately 70 ml/beat. It is important to monitor this number as it can indicate potential cardiac issues such as congestive heart failure.

Clinical Relevance: Heart Murmurs

Heart murmurs are abnormal heart sounds caused by turbulent blood flow. These sounds can be low-pitched whooshing noises, or higher pitched clicking or buzzing noises. They are usually heard through a stethoscope, but in some cases may be present without one.

The causes of heart murmurs can vary. Some murmurs can be innocent and harmless, caused by physical activity or even stress and anxiety. However, they can also be an indicator of underlying heart problems such as valve diseases, structural malformations, and certain infections.

It is important to understand the various types of heart murmurs to accurately diagnose any underlying issues. Murmurs can be classified into different categories, such as systolic murmurs, diastolic murmurs, and continuous murmurs. Each type of murmur has its own distinct characteristics, including frequency, intensity, and quality of sound.

Murmurs can also be graded on a scale from 1 to 6, with 6 being the most severe. Grading is based on several factors such as loudness, timing, and location on the chest wall. Knowing how to grade murmurs can help a physician determine the severity of the condition and the best treatment plan.

When a patient presents with a heart murmur, they should be further evaluated to rule out any serious underlying conditions. This might include a physical examination, laboratory tests, imaging studies, or cardiac catheterization. Once the underlying cause is determined, an appropriate treatment plan can be devised to treat the condition.

Key Points

  • The cardiac cycle consists of atrial systole, ventricular systole, and diastole.
  • Wiggers' diagram is a visual representation of the pressure changes during the cycle.
  • Cardiac volumes refer to the amount of blood in the ventricles at the end of the systole and diastole.
  • Heart murmurs are abnormal sounds heard on examination and may suggest the presence of structural heart disease.

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