In clinical

cardiology Cardiology () is a branch of medicine that deals with disorders of the heart and the cardiovascular system. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular he ...

the term "diastolic function" is most commonly referred as how the

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

fills. Parallel to "diastolic function", the term " systolic function" is usually referenced in terms of the left ventricular

ejection fraction An ejection fraction (EF) is the volumetric fraction (mathematics), fraction (or portion of the total) of fluid (usually blood) ejected from a chamber (usually the heart) with each contraction (or cardiac cycle, heartbeat). It can refer to the card ...

(LVEF), which is the ratio of

stroke volume In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood ...

and

end-diastolic volume In cardiovascular physiology, end-diastolic volume (EDV) is the volume of blood in the right or left ventricle at end of filling in diastole which is ammount of blood present in ventricle at the end of diastole systole. Because greater EDVs cause g ...

. Due to the epidemic of

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...

, particularly the cases determined as diastolic heart failure, it is increasingly urgent and crucial to understand the meaning of “diastolic function”. Unlike "systolic function", which can be simply evaluated by LVEF, there are no established dimensionless parameters for "diastolic function" assessment. Hence to further study "diastolic function" the complicated and speculative physiology must be taken into consideration. How the heart works during its filling period still has many misconceptions remaining. To better understand diastolic function, it is crucial to realize that the left ventricle is a mechanical suction pump at, and for a little while after, the

mitral valve The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one- ...

opening. In other words, when mitral valve opens, the atrium does not push

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in th ...

into the ventricle, instead, it is the ventricle that mechanically "sucks" in blood from the atrium. The energy that drives the suction process is generated from phase of

systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ' ...

. During systole, to overcome the peripheral arterial load at ejection, ventricle contracts, which also compresses elastic tissues internal to and external to the

myocardium Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

. Then, when

cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

relaxes, the energy captured by compressed elements releases, driving the recoil of ventricular wall until a new balanced equilibrium state is reached. During

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventri ...

, the ventricle of heart must remain elastic or compliant enough and have capacity to hold incoming blood to guarantee effectiveness of the filling phase. Hence stiffness and relaxation are ventricle's intrinsic feature parameters that are practical in evaluating and quantifying diastolic function. In addition,

volumetric load Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The defi ...

serves as an extrinsic indicating parameter that modulates diastolic function. __TOC__

Measurement

The most established index to describe left ventricular diastolic function is Tau, left ventricular diastolic time constant. Measurement of Tau is traditionally delivered in a catheter lab by an invasive method. Recently, non-invasive measurement of Tau is available for mitral regurgitation or aortic regurgitation patients in an Echo lab. There have been many attempts intending for extracting both intrinsic and extrinsic properties. Early attempts concentrated on pulse-wave Doppler-echo measured trans-mitral flow velocity contours. In terms of filling, diastolic intervals consist of early rapid filling E-waves followed by diastasis and followed by atrial systole-generated A-waves. Empirically, E- and A- wave contours were simplified as triangles. Nowadays, triangle-based indexes, such as the peak velocities of the E- and A-waves and ratio of them, the deceleration time and time duration of the E-wave, and the velocity time integral of both E- and A- waves, are usually measured and evaluated. The triangular approach applies to E-wave shape conveniently, especially in the past when the images rendered by technology back in days are of poor resolution quality. Nevertheless, with rapidly improving temporal resolution and image processing capabilities, the curvature of E-wave contours can be clearly identified with detailed information revealed. Due to advancement of modern medical imaging technology, the measurement of even smaller (i.e. tissue) velocities are possible to be made, which even leads to capability to measure the longitudinal displacements of the

mitral annulus The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all ...

. The shapes of mitral annular velocity contours used to be approximated to be triangles, whose peak height is label to be E’. E’ proved useful in selected patient populations for estimation of

end-diastolic pressure In cardiac physiology, preload is the amount of sarcomere stretch experienced by cardiac muscle cells, called cardiomyocytes, at the end of ventricular filling during diastole. Preload is directly related to ventricular filling. As the relaxed v ...

(EDP). Other innovative imaging modalities consist of techniques such as speckle tracking. Speckle tracking enables strain and strain-rate measurements. It is a relatively recent instance of technological progress, due to the fact that it relies on the information content inherent in the seemingly random arrangement of bright speckles present in all echocardiographic images. Even though a variety of echo-based imaging technologies represent multiple levels of research innovation, much remains to be studied in relation to how to interpret the recorded data embedded in images.

References

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