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Diastole ( ) is the relaxed phase of the
cardiac cycle The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followin ...
when the chambers of the heart are re-filling with blood. The contrasting phase is
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 ...
when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricular diastole the relaxing of the ventricles. The term originates from the Greek word (''diastolē''), meaning "dilation", from (''diá'', "apart") + (''stéllein'', "to send").


Role in cardiac cycle

A typical heart rate is 75 beats per minute (bpm), which means that the cardiac cycle that produces one heartbeat, lasts for less than one second. The cycle requires 0.3 sec in ventricular systole (contraction)—pumping blood to all body systems from the two ventricles; and 0.5 sec in diastole (dilation), re-filling the four chambers of the heart, for a total of 0.8 sec to complete the cycle.


Early ventricular diastole

During early ventricular diastole, pressure in the two ventricles begins to drop from the peak reached during systole. When the pressure in the left ventricle falls below that in the left atrium, 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 on ...
opens due to a negative pressure differential (suction) between the two chambers. The open mitral valve allows blood in the atrium (accumulated during atrial diastole) to flow into the ventricle (see graphic at top). Likewise, the same phenomenon runs simultaneously in the right ventricle and right atrium through the
tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ven ...
. The ventricular filling flow (or flow from the atria into the ventricles) has an early (E) diastolic component caused by ventricular suction, and then a late one created by
atrial systole The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followin ...
(A). The
E/A ratio The E/A ratio is a marker of the function of the left ventricle of the heart. It represents the ratio of peak velocity blood flow from left ventricular relaxation in early diastole (the E wave) to peak velocity flow in late diastole caused by atria ...
is used as a diagnostic measure as its diminishment indicates probable
diastolic dysfunction Heart failure with preserved ejection fraction (HFpEF) is a form of heart failure in which the ejection fraction – the percentage of the volume of blood ejected from the left ventricle with each heartbeat divided by the volume of blood when the l ...
.


Late ventricular diastole

Early diastole is a suction mechanism between the atrial and ventricular chambers. Then, in late ventricular diastole, the two atrial chambers contract (atrial systole), causing blood pressure in both atria to increase and forcing additional blood flow into the ventricles. This beginning of the atrial systole is known as the ''atrial kick''—see Wiggers diagram. The atrial kick ''does not'' supply the larger amount of flow (during the cardiac cycle) as about 80 percent of the collected blood volume flows into the ventricles during the active suction period.


Atrial diastole

At the beginning of the cardiac cycle the atria, and the ventricles are synchronously approaching and retreating from relaxation and dilation, or diastole. The atria are filling with separate blood volumes returning to the right atrium (from the
vena cavae In anatomy, the venae cavae (; singular: vena cava ; ) are two large veins (great vessels) that return deoxygenated blood from the body into the heart. In humans they are the superior vena cava and the inferior vena cava, and both empty into the ...
), and to the left atrium (from the lungs). After chamber and back pressures equalize, the mitral and tricuspid valves open, and the returning blood flows through the atria into the ventricles. When the ventricles have completed most of their filling, the atria begin to contract (atrial systole), forcing blood under pressure into the ventricles. Now the ventricles start to contract, and as pressures within the ventricles rise, the mitral and tricuspid valves close producing the
first heart sound Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stet ...
(S1) as heard with a stethoscope. As pressures within the ventricles continue to rise, they exceed the "back pressures" in the
aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes o ...
, and the
pulmonary trunk A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and ...
. The aortic and pulmonary valves known as the
semilunar valves A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart v ...
open, and a defined fraction of blood within the heart is ejected into the aorta and pulmonary trunk. Ejection of blood from the heart is known as
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 ...
. Ejection causes pressure within the ventricles to fall, and, simultaneously, the atria begin to refill (atrial diastole). Finally, pressures within the ventricles fall below the back pressures in the aorta and the pulmonary arteries, and the semilunar valves close. Closure of these valves give the
second heart sound Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stetho ...
(S2). The ventricles then start to relax, the mitral and tricuspid valves begin to open, and the cycle begins again. In summary, when the ventricles are in systole and contracting, the atria are relaxed and collecting returning blood. When, in late diastole, the ventricles become fully dilated (understood in imaging as LVEDV and RVEDV), the atria begin to contract, pumping blood to the ventricles. The atria feed a steady supply of blood to the ventricles, thereby serving as a reservoir to the ventricles and ensuring that these pumps never run dry. This coordination ensures that blood is pumped and circulated efficiently throughout the body.


Clinical notation

Blood pressure is usually written with the systolic pressure expressed over the diastolic pressure or separated by a
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, for example, 120/80 
mmHg A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted mmHg or mm Hg. Although not an ...
. This clinical notation is not a mathematical figure for a fraction or ratio, nor a display of a numerator over a denominator, rather it is a medical notation showing the two clinically significant pressures involved. It is often shown followed by a third value, the number of beats per minute of the
heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
. Mean blood pressure is also an important determinant in people who have had certain medical interventions like Left Ventricular Assist Devices (LVAD) and
hemodialysis Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinin ...
that replace pulsatile flow with continuous blood flow.


Diagnostic value

Examining diastolic function during a
cardiac stress test A cardiac stress test (also referred to as a cardiac diagnostic test, cardiopulmonary exercise test, or abbreviated CPX test) is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical enviro ...
is a good way to test for
heart failure with preserved ejection fraction Heart failure with preserved ejection fraction (HFpEF) is a form of heart failure in which the ejection fraction – the percentage of the volume of blood ejected from the left ventricle with each heartbeat divided by the volume of blood when the ...
. Classification of
blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure ...
in adults:


Effects of impaired diastolic function

Brain natriuretic peptide Brain natriuretic peptide 32 (BNP), also known as B-type natriuretic peptide, is a hormone secreted by cardiomyocytes in the heart ventricles in response to stretching caused by increased ventricular blood volume. Along with NT-proBNP, BNP is one ...
(BNP) is a cardiac neurohormone secreted from ventricular myocytes (ventricular muscle cells) at the end of diastole—this in response to the normal, or sub-normal (as the case may be), stretching of cardiomyocytes (heart muscle cells) during systole. Elevated levels of BNP indicate excessive natriuresis (excretion of sodium to the urine) and decline of ventricular function, especially during diastole. Increased BNP concentrations have been found in patients who experience
diastolic heart failure Heart failure with preserved ejection fraction (HFpEF) is a form of heart failure in which the ejection fraction – the percentage of the volume of blood ejected from the left ventricle with each heartbeat divided by the volume of blood when the ...
. Impaired diastolic function can result from the ''decreased compliance of ventricular myocytes'', and thus the ventricles, which means the heart muscle does not stretch as much as needed during filling. This will result in a reduced
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 ...
(EDV) and, according to the Frank-Starling mechanism, a reduced EDV will lead to a reduced stroke volume, thus a reduced
cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: th ...
. Over time, decreased cardiac output will diminish the ability of the heart to circulate blood efficiently throughout the body. Degradation of compliance in the myocardium is a natural consequence of aging.


References


External links

{{Cardiovascular physiology Blood pressure