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Afterload is the pressure that the heart must work against to eject blood during systole (ventricular contraction). Afterload is proportional to the average arterial pressure. As aortic and pulmonary pressures increase, the afterload increases on the left and right ventricles respectively. Afterload changes to adapt to the continually changing demands on an animal's cardiovascular system. Afterload is proportional to mean systolic blood pressure and is measured in millimeters of mercury (mm Hg).




Hemodynamics


Afterload is a determinant of cardiac output. Cardiac output is the product of stroke volume and heart rate. Afterload is a determinant of stroke volume (in addition to preload, and strength of myocardial contraction).
Following Laplace's law, the tension upon the muscle fibers in the heart wall is the pressure within the ventricle multiplied by the volume within the ventricle divided by the wall thickness (this ratio is the other factor in setting the afterload). Therefore, when comparing a normal heart to a heart with a dilated left ventricle, if the aortic pressure is the same in both hearts, the dilated heart must create a greater tension to overcome the same aortic pressure to eject blood because it has a larger internal radius and volume. Thus, the dilated heart has a greater total load (tension) on the myocytes, i.e., has a higher afterload. This is also true in the eccentric hypertrophy consequent to high-intensity aerobic training. Conversely, a concentrically hypertrophied left ventricle may have a lower afterload for a given aortic pressure. When contractility becomes impaired and the ventricle dilates, the afterload rises and limits output. This may start a vicious circle, in which cardiac output is reduced as oxygen requirements are increased.
Afterload can also be described as the pressure that the chambers of the heart must generate to eject blood from the heart, and this is a consequence of aortic pressure (for the left ventricle) and pulmonic pressure or pulmonary artery pressure (for the right ventricle). The pressure in the ventricles must be greater than the systemic and pulmonary pressure to open the aortic and pulmonic valves, respectively. As afterload increases, cardiac output decreases. Cardiac imaging is a somewhat limited modality in defining afterload because it depends on the interpretation of volumetric data.




Calculating afterload


Quantitatively, afterload can be calculated by determining the wall stress of the left ventricle, using the Young–Laplace equation:





(



E
D
P
⋅
E
D
R


2
h



)



{\textstyle \left({\frac {EDP\cdot EDR}{2h}}\right)}

where
EDP is end-diastolic pressure in the left ventricle, which is typically approximated by taking pulmonary artery wedge pressure,
EDR is end-diastolic radius at the midpoint of the left ventricle, and
h is the mean thickness of the left ventricle wall. Both radius and mean thickness of the left ventricle may be measured by echocardiography.




Factors affecting afterload


Disease processes pathology that include indicators such as an increasing left ventricular afterload include elevated blood pressure and aortic valve disease.
Systolic hypertension (HTN) (elevated blood pressure) increases the left ventricular (LV) afterload because the LV must work harder to eject blood into the aorta. This is because the aortic valve won't open until the pressure generated in the left ventricle is higher than the elevated blood pressure in the aorta.
Pulmonary hypertension (PH) is increased blood pressure within the right heart leading to the lungs. PH indicates a regionally applied increase in afterload dedicated to the right side of the heart, divided and isolated from the left heart by the interventricular septum.
In the natural aging process, aortic stenosis often increases afterload because the left ventricle must overcome the pressure gradient caused by the calcified and stenotic aortic valve, in addition to the blood pressure required to eject blood into the aorta. For instance, if the blood pressure is 120/80, and the aortic valve stenosis creates a trans-valvular gradient of 30 mmHg, the left ventricle has to generate a pressure of 110 mmHg to open the aortic valve and eject blood into the aorta.
Due to the increased afterload, the ventricle has to work harder to accomplish its goal of ejecting blood into the aorta. Thus, in the long-term, increased afterload (due to the stenosis) results in hypertrophy of the left ventricle to account for the increased work required and also to decrease wall stress since wall thickness and wall stress are inversely proportional.
Aortic insufficiency (Aortic Regurgitation) increases afterload, because a percentage of the blood that ejects forward regurgitates back through the diseased aortic valve. This leads to elevated systolic blood pressure. The diastolic blood pressure in the aorta falls, due to regurgitation. This increases pulse pressure.
Mitral regurgitation (MR) decreases afterload. In ventricular systole under MR, regurgitant blood flows backwards/retrograde back and forth through a diseased and leaking mitral valve. The remaining blood loaded into the LV is then optimally ejected out through the aortic valve. With an extra pathway for blood flow through the mitral valve, the left ventricle does not have to work as hard to eject its blood, i.e. there is a decreased afterload. Afterload is largely dependent upon aortic pressure.




See also


Cardiac output
Hemodynamics
Preload




References






Further reading


Ross, John (1976). "Afterload mismatch and preload reserve: A conceptual framework for the analysis of ventricular function". Progress in Cardiovascular Diseases. 18 (4): 255–264. doi:10.1016/0033-0620(76)90021-9. PMID 128034.
Kasper, W.; Konstantinides, S.; Geibel, A.; Tiede, N.; Krause, T.; Just, H. (1997). "Prognostic significance of right ventricular afterload stress detected by echocardiography in patients with clinically suspected pulmonary embolism". Heart. 77 (4): 346–349. doi:10.1136/hrt.77.4.346. PMC 484729. PMID 9155614.
Mahler, Felix; Ross, John; O'Rourke, Robert A.; Covell, James W. (1975). "Effects of changes in preload, afterload and inotropic state on ejection and isovolumic phase measures of contractility in the conscious dog". The American Journal of Cardiology. 35 (5): 626–634. doi:10.1016/0002-9149(75)90048-X. PMID 1124716.
Hachicha, Z.; Dumesnil, J. G.; Bogaty, P.; Pibarot, P. (2007). "Paradoxical Low-Flow, Low-Gradient Severe Aortic Stenosis Despite Preserved Ejection Fraction is Associated with Higher Afterload and Reduced Survival". Circulation. 115 (22): 2856–2864. doi:10.1161/CIRCULATIONAHA.106.668681. PMID 17533183.
Kelly, R. P.; Gibbs, H. H.; O'Rourke, M. F.; Daley, J. E.; Mang, K; Morgan, J. J.; Avolio, A. P. (1990). "Nitroglycerin has more favourable effects on left ventricular afterload than apparent from measurement of pressure in a peripheral artery". European Heart Journal. 11 (2): 138–144. doi:10.1093/oxfordjournals.eurheartj.a059669. PMID 2107077.




External links


Overview at cvphysiology.com

Kata Kunci Pencarian:

• Amlodipin
• Milrinon
• Natrium nitroprusida
• Prazosin
• Hidralazin
• Angina pektoris tidak stabil
• Terapi oksigen
• Penghalang saluran kalsium
• Antiangina
• Afterload
• Stroke volume
• Pressure–volume loop analysis in cardiology
• Anrep effect
• Intra-aortic balloon pump
• Heart murmur
• Vasodilation
• Left ventricular hypertrophy
• Impedance cardiography
• Cardiac physiology

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Daftar Isi

• Understanding Preload and Afterload in Cardiac Output - Simple …
• Afterload - Wikipedia
• Physiology, Afterload Reduction - StatPearls - NCBI Bookshelf
• Cardiac Afterload - CV Physiology
• Cardiac Preload vs Afterload vs Contractility |With an example
• Afterload • LITFL Medical Blog • CCC Cardiology
• What is the Difference Between Preload and Afterload
• What is Afterload and Preload? | Heart Dynamics Explained
• Preload and Afterload – CARDS RX (explained)
• Determinants of afterload - Deranged Physiology

Understanding Preload and Afterload in Cardiac Output - Simple …

Jul 2, 2024 · Basically, afterload is the amount of pressure that the heart has to overcome to enter the next phase, whether the blood will go inside the lungs or the peripherals. Afterload is also known as the systolic pressure inside the blood vessels.

Afterload - Wikipedia

Afterload is the pressure that the heart must work against to eject blood during systole (ventricular contraction). Afterload is proportional to the average arterial pressure. [ 1 ] As aortic and pulmonary pressures increase, the afterload increases on the left and right ventricles respectively.

Physiology, Afterload Reduction - StatPearls - NCBI Bookshelf

Apr 24, 2023 · The afterload of any contracting muscle is defined as the total force that opposes sarcomere shortening minus the stretching force that existed before contraction. Applying this definition to the heart, afterload can be most easily described as …

Cardiac Afterload - CV Physiology

Afterload can be thought of as the "load" that the heart must eject blood against. In simple terms, the afterload of the left ventricle is closely related to the aortic pressure. The afterload on individual muscle fibers within the wall of the heart is often expressed as ventricular wall stress (σ) and described by the following equation:

Cardiac Preload vs Afterload vs Contractility |With an example

Dec 28, 2023 · Cardiac afterload is the pressure that the ventricles have to generate in order to pump the blood out of semilunar valves. The pressure in the aorta is approximately 80 mmHg and the pressure in the pulmonary trunk is 10 mmHg. Changes in cardiac afterload have a negative effect on stroke volume (SV).

Afterload • LITFL Medical Blog • CCC Cardiology

Afterload = left ventricular wall tension required to overcome resistance to ejection (impedance to ejection of blood from the heart into the arterial circulation). developed as ventricular muscle fibres shorten during isovolumetric contraction & ejection phases of systole.

What is the Difference Between Preload and Afterload

Aug 30, 2023 · The main difference between preload and afterload is that preload is the pressure that occurs at the initial stretching of the cardiac myocytes, whereas afterload is the force that occurs when the heart pumps blood.

What is Afterload and Preload? | Heart Dynamics Explained

Afterload refers to the resistance the heart must overcome to eject blood, while preload is the initial stretching of the cardiac muscle before contraction. Understanding the concepts of afterload and preload is crucial for grasping how the heart functions.

Preload and Afterload – CARDS RX (explained)

Nov 12, 2021 · The higher the afterload, the harder your heart has to contract to ensure forward flow and perfusion to the rest of the body. Let’s talk about what factors can increase afterload. Patients with an issue with their aortic valve (the valve that separates the left ventricle from the aorta), known as aortic stenosis , have increased afterload.

Determinants of afterload - Deranged Physiology

Apr 28, 2020 · Afterload can be defined as the resistance to ventricular ejection - the "load" that the heart must eject blood against. It consists of two main sets of determinant factors: P, the ventricular transmural pressure, which is the difference between the ventricular cavity pressure and the intrathoracic pressure.