Ejection Phase – Cardiac Cycle Explained
The ejection phase is the part of the cardiac cycle in which the heart pumps blood into the arteries. It is essential for supplying the body with oxygen-rich blood.
Things worth knowing about "Ejection Phase"
The ejection phase is the part of the cardiac cycle in which the heart pumps blood into the arteries. It is essential for supplying the body with oxygen-rich blood.
What is the Ejection Phase?
The ejection phase (also called the ventricular ejection phase or ejection period) is a key segment of the cardiac cycle. It describes the period during which the ventricles (lower chambers of the heart) contract and actively pump blood into the major arteries – the aorta (from the left ventricle) and the pulmonary artery (from the right ventricle). The ejection phase is a fundamental component of the systole, which refers to the contraction phase of the heartbeat.
The Ejection Phase Within the Cardiac Cycle
The cardiac cycle consists of two main phases: systole (contraction) and diastole (relaxation and filling). The ejection phase occurs during systole and follows the isovolumetric contraction phase, during which pressure builds up in the ventricles without any blood being ejected.
- Isovolumetric contraction: All heart valves are closed and ventricular pressure rises rapidly.
- Ejection phase: Once ventricular pressure exceeds the pressure in the aorta or pulmonary artery, the semilunar valves (aortic and pulmonary valves) open and blood is pumped into the circulation.
- Diastole (relaxation): After ejection, the valves close again, and the ventricles refill with blood.
Rapid and Reduced Ejection
The ejection phase is commonly divided into two sub-phases:
- Rapid ejection: During this initial sub-phase, the majority of the blood – approximately two-thirds of the stroke volume – is ejected quickly and forcefully. Aortic pressure reaches its peak, known as systolic blood pressure.
- Reduced ejection: In this second sub-phase, the rate of ejection slows down, the remaining blood volume is expelled, and ventricular pressure begins to fall.
Stroke Volume and Ejection Fraction
The amount of blood ejected per heartbeat is called the stroke volume. At rest in a healthy adult, this is typically around 60–80 ml. A key clinical parameter is the ejection fraction (EF), which indicates what percentage of the blood in the ventricle is actually ejected with each beat. A healthy heart has an ejection fraction of approximately 55–70%. A reduced ejection fraction (below 50%) may indicate heart failure.
Clinical Relevance
The ejection phase is of great clinical importance, as many heart conditions impair its function. Common disorders affecting the ejection phase include:
- Heart failure (systolic dysfunction): The heart cannot pump sufficient blood, leading to fatigue, shortness of breath, and fluid retention.
- Aortic stenosis: Narrowing of the aortic valve increases resistance to blood ejection and places additional strain on the heart.
- Aortic regurgitation: Blood flows back into the left ventricle after ejection, reducing the efficiency of the ejection phase.
- Cardiomyopathies: Diseases of the heart muscle that can reduce contractile force and therefore stroke volume.
Diagnosis of the Ejection Phase
Several diagnostic tools are used in clinical practice to assess the function of the ejection phase:
- Echocardiography (cardiac ultrasound): The primary method for measuring stroke volume and ejection fraction. It allows real-time visualization of heart wall movement and valve function.
- ECG (electrocardiogram): Detects arrhythmias that may affect the ejection phase.
- Cardiac catheterization: Allows direct pressure measurement in the heart chambers and aorta.
- Cardiac MRI: Provides precise volumetric measurements and detailed information about myocardial structure.
References
- Guyton A.C., Hall J.E. - Textbook of Medical Physiology, 13th Edition. Elsevier, Philadelphia, 2016.
- McMurray J.J.V. et al. - ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. European Heart Journal, 2012; 33(14): 1787-1847.
- Katz A.M. - Physiology of the Heart, 5th Edition. Lippincott Williams and Wilkins, Philadelphia, 2011.
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