Diastole

Diastole /daɪˈæstəliː/ is the part of the cardiac cycle during which the heart refills with blood after the emptying done during systole (contraction). Ventricular diastole is the period during which the two ventricles are relaxing from the contortions/wringing of contraction, then dilating and filling; atrial diastole is the period during which the two atria likewise are relaxing under suction, dilating, and filling. The term diastole originates from the Greek word διαστολή, meaning dilation. Evidence thus provided shows Diastole is not a passive phase. Diastole /daɪˈæstəliː/ is the part of the cardiac cycle during which the heart refills with blood after the emptying done during systole (contraction). Ventricular diastole is the period during which the two ventricles are relaxing from the contortions/wringing of contraction, then dilating and filling; atrial diastole is the period during which the two atria likewise are relaxing under suction, dilating, and filling. The term diastole originates from the Greek word διαστολή, meaning dilation. Evidence thus provided shows Diastole is not a passive phase. For a healthy human heart the entire cardiac cycle typically runs less than one second. That is, for a typical heart rate of 75 beats per minute (bpm), 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 time of 0.8 sec to complete the entire cycle. During early ventricular diastole, pressure in the two ventricles begins to drop from the peak reached during systole. When pressure in the left ventricle falls below that in the left atrium the mitral valve opens due to a negative pressure differential (suction) between the two chambers, causing 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 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 (A). The E/A ratio is used as a diagnostic measure as its diminishment indicates probable diastolic dysfunction. 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 per cent of the collected blood volume flows into the ventricles during the active suction period. At the beginning of the cardiac cycle, all four chambers of the heart, two atria and two ventricles are synchronously approaching relaxation and dilation, or diastole. The atria are filling with separate blood volumes returning to the right atrium (from the vena cavae) and to the left atrium (from the lungs). After chamber and back pressures equalize, the mitral and tricuspid valves open, and the 'return' blood flows are passed 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 are closed. As pressures within the ventricles continue to rise, they exceed the 'back pressures' in the aorta trunk and the pulmonary arteries trunk, and the aortic and pulmonary valves open—and now blood is ejected from the heart. 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 trunks of the aorta and the pulmonary arteries, and the aortic and pulmonary valves close. The ventricles 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 blood as 'return' flows. 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. Here the adjective 'diastolic' refers to the function (the 'diastolic function') of filling the heart with blood between muscle contractions; it describes that portion of the cardiac cycle opposite to contraction. The term is more commonly known as one of the two main components for measuring blood pressure—namely, 'diastolic pressure' refers to the lowest pressure in the arterial bloodstream occurring during each heartbeat. (The other component is 'systolic pressure', which is the highest arterial pressure during each heartbeat.)