User:Bakerstmd/Ejection fraction

Ejection fraction (EF) is the fraction of blood pumped from the heart with each heartbeat. It is commonly measured by echocardiogram and serves as a general measure of a person's cardiac function. Ejection fraction is typically low in patients with congestive heart failure.

Ejection fraction is similar but distinct from stroke volume, which (along with heart rate) determines cardiac output, which is the amount of blood the heart pumps per minute.

Medical uses
The ejection fraction is a crucial determinant of the severity of coronary artery disease, congenital heart disease, conduction disease, cardiac infectious disease, granulomatous disease and resulting systolic heart failure.

Measurement
Ejection fraction is commonly measured by echocardiography, in which the volumes of the heart's chambers are measured during the cardiac cycle. Ejection fraction can then be obtained by dividing stroke volume by end-diastolic volume as described above.

Ejection fraction can also be measured by computed tomography (CT scan), magnetic resonance imaging (MRI), ventriculography, gated SPECT and radionuclide angiography (MUGA) scanning. A MUGA scan involves the injection of a radioisotope into the blood and detecting its flow through the left ventricle. The gold standard for measurement of the ejection fraction historically is ventriculography.

Accurate volumetric measurement of performance of the right and left ventricles of the heart is inexpensively and routinely echocardiographically interpreted worldwide as a ratio of the dimension between the ventricles in systole and diastole. For example, a ventricle in greatest dimension could measure 6 cm while in least dimension 4 cm. Measured and easily reproduced beat to beat for ten or more cycles, this ratio may represent a physiologically normal EF of 50-60%. Mathematical expression of this time-dependent ratio can then be interpreted as an opening coil half as cardiac output and a closing recoil half as cardiac input. CO=CI

Imaging of the heart allows for mathematical expressions defining flow of blood in and out of the heart. Cardiac Imaging uses visually enhanced mathematics of the folding and unfolding of the myocardium focused on a single cardiac cycle.

Normal values
In a healthy 70 kg man, the SV is approximately 70 mL and the left ventricular EDV is 120 mL, giving an ejection fraction of $70/120$, or 0.58 (58%).

Right ventricular volumes being roughly equal to those of the left ventricle, the ejection fraction of the right ventricle physiologically matches that of the left ventricle within mathematically narrow beat-to-beat limits.

Healthy individuals typically have ejection fractions between 50% and 65%. However, normal values depend upon the modality being used to calculate the ejection fraction, and some sources consider an ejection fraction of 55% to 75% to be normal. Damage to the muscle of the heart (myocardium), such as that sustained during myocardial infarction or in atrial fibrillation or a plurality of etiologies of cardiomyopathy, compromises the heart's ability to perform as an efficient pump (ejecting blood) and, therefore, reduces ejection fraction. This reduction in the ejection fraction can manifest itself clinically as heart failure. A low ejection fraction has its cutoff below 40% with symptomatic manifestations constant at 25%. In the USA, a chronically low ejection fraction less than 30% is qualifying support for eligibility of disability benefits from the Social Security Administration.

Healthy older adults favorably adapt as the ventricles become less compliant and are routinely echocardiographically proven to have an EF from 55–85% with the help of good genetics and a healthy lifestyle. Compliance, defined as

$$ \frac{d(volume)}{d(pressure)} $$

is a property of the heart that allows contractility. Encyclopedic documentation of the commonly documented "hyperdynamic" ventricle remains sparse.

The ejection fraction is one of the most important predictors of prognosis; those with significantly reduced ejection fractions typically have poorer prognoses. However, recent studies have indicated that a preserved ejection fraction does not mean freedom from risk.

The QT interval as recorded on a standard electrocardiogram (EKG) represents ventricular depolarazation and ventricular repolarazation and is rate-dependent.

Physics
In mathematics allowed by medical imaging, EF is applied to both the right ventricle, which ejects blood via the pulmonary valve into the pulmonary circulation, and the left ventricle, which ejects blood via the aortic valve into the cerebral and systemic circulation.

EF is essentially a ratio; a mathematical expression of forward movement of blood out of the heart contrasted to the amount retained in a single cardiac cycle. One important mathematical expression involves easily reproduced volumetrics.

By definition, the volume of blood within a ventricle immediately before a contraction is known as the end-diastolic volume (EDV). Likewise, the volume of blood left in a ventricle at the end of contraction is end-systolic volume (ESV). The difference between EDV and ESV represents a ratio between the ventricles full and emptied. This ratio allows many variables such as stroke volume (SV) and Cardiac Output (CO). SV describes the volume of blood ejected from the right and left ventricles with each heartbeat. Ejection fraction is the fraction of the end-diastolic volume that is ejected with each beat; that is, it is stroke volume (SV) divided by end-diastolic volume (EDV):

$$E_f (\%) = \frac{SV}{EDV}\times100$$

Where the stroke volume is given by:

$$SV = EDV - ESV$$

History
As a volumetric mathematical term, ejection fraction is an extension of work by Adolph Fick entitled Cardiac Output. Fick's theory was gradually merged to fit the precision of wall motion mathematics first defined by Laplace. This led to the introduction of compliance or Delta V (volume)/ Delta P (pressure). Myocardial compliance represents a generic variable ratio between Pressure and Volume. Applied to the heart, this appreciation led to further progress represented by length-tension constructs I. e. the Frank–Starling law of the heart. Youngs' Modulus leant itself to Elasticity, another ratio of stress and strain. The gathered mathematics eventually birthed medical imaging, gradually followed by Cardiac Imaging.