Diastole

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Diastole is that 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 of contraction, then dilating and filling; atrial diastole is the period during which the two atria likewise are relaxing, dilating, and filling. The term diastole originates from the Greek word ????????, meaning dilation.

Video Diastole

Role in cardiac cycle

For a healthy human heart the entire cardiac cycle typically runs less than one second. That is, for a normal heart rate of 72 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 it's 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.

Maps Diastole

Diastolic pressure

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.)

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Clinical notation

When blood pressure is stated for medical purposes, it is usually written with the systolic and diastolic pressures separated by a slash, for example, 120/80 mmHg. 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 (i.e., systolic-slash-diastolic, or 120/80). It is often shown followed by a third number, the value of the heart rate (in beats per minute), which typically is measured jointly with blood pressure readings.

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Diagnostic value

Examining diastolic function during a cardiac stress test is a good way to test for heart failure with preserved ejection fraction.

Classification of Blood Pressure in Adults

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Effects of impaired diastolic function

Brain natriuretic peptide (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.

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 (EDV) and, according to the Frank-Starling mechanism, a reduced EDV will lead to a reduced stroke volume, thus a reduced cardiac output. Over time, decreased cardiac output will diminish the ability of the heart to circulate blood efficiently throughout the body.

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See also

• Systole (medicine)
• Blood pressure
• Wiggers diagram

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References

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External links

Source of the article : Wikipedia