Diastole

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Heart during ventricular diastole.

Diastole /dˈæstəl/ is the part of the cardiac cycle when the heart refills with blood following systole (contraction). Ventricular diastole is the period during which the ventricles are filling and relaxing, while atrial diastole is the period during which the atria are relaxing. The term diastole originates from the Greek word διαστολη, meaning dilation.[1]

Role in cardiac cycle[edit]

Wiggers diagram, showing various events during diastole (duration marked at bottom).

Typically, for a heart rate of 72 beats/minute, a cardiac cycle lasts approximately 0.8 sec, 0.3 sec spent in systole, and 0.5 sec in diastole.[2]

During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral valve opens, causing accumulated blood from the atrium to flow into the ventricle.

The ventricular filling velocity or flow into the ventricles have two main components; First an early (E) diastolic one caused ventricular suction, and second, a late one created by atrial contraction (A). The E/A ratio can be used as a diagnostic measure, since it is reduced in diastolic dysfunction.[3]

Early diastole, i.e., the E-wave in the E/A ratio, is a suction mechanism.[4] In late diastole, i.e., the A-wave, as the left and right atria contract, the blood pressure in each atrium increases, forcing additional blood into the ventricles. This is known as atrial kick. 80% of the blood flows passively down to the ventricles during the E-wave active suction period, so the atria do not have to contract a great amount.[5]

Arterial pressure[edit]

The adjective "diastolic" is used to refer to filling of the heart with blood between muscle contractions. It is used to describe the opposite portion of the cardiac cycle related to contraction. More typically it is used as one component of measurement of blood pressure. "Diastolic pressure" refers to the lowest pressure within the arterial bloodstream occurring during each heartbeat. The other component of blood pressure is systolic pressure, which refers to the highest arterial pressure during each heartbeat.

Clinical notation[edit]

When blood pressure is stated for medical purposes, it is usually written as a seeming "ratio" of systolic to diastolic pressure; for example: 120/80 mmHg. This is not intended to be read as a ratio and for the vast majority of purposes cannot be legitimately read as a ratio. It is not a display of a numerator over a denominator but rather a medical notation used for quickly showing the two clinically significant pressures involved and cannot be reduced into lower terms.

Diagnostic value[edit]

Examining diastolic function during a cardiac stress test is a good way to test for heart failure with preserved ejection fraction.[6]

Classification of Blood Pressure in Adults[7]

Blood Pressure Classification Systolic BP (mmHg) Diastolic BP (mmHg)
Optimal <120 and <80
Prehypertension 120–139 or 80–89
Stage 1 Hypertension 140–159 or 90–99
Stage 2 Hypertension ≥160 or ≥100

Effects of impaired diastolic function[edit]

Brain natriuretic peptide (BNP) is a cardiac neurohormone secreted from ventricular myocytes at the end of diastole in response to stretching experienced by cardiomyocytes. Elevated levels of BNP indicate excessive natriuresis and decline of ventricular function, especially during diastole. Increased BNP concentrations have been found in patients who experience specifically diastolic heart failure.[8]

Impaired diastolic function can result from the decreased compliance of the ventricles, which means the heart cannot stretch as much during filling.[2] This will result in a reduced end diastolic volume (EDV). According to Frank-Starling forces, a reduced EDV will lead to a reduced stroke volume, thus a reduced cardiac output. Over time, this decreased cardiac output will diminish the ability of the heart to circulate blood efficiently throughout the body.

See also[edit]

References[edit]

  1. ^ Diastole. Merriam-Webster Online Dictionary. 24 August 2008.
  2. ^ a b Widmaier, Eric P. (2014). Vander's Human Physiology: The Mechanisms of Body Function, 13/e. McGraw Hill Education. p. 378. 
  3. ^ Mohamed, A. L.; Yong, J; Masiyati, J; Lim, L; Tee, S. C. (2004). "The prevalence of diastolic dysfunction in patients with hypertension referred for echocardiographic assessment of left ventricular function". The Malaysian Journal of Medical Sciences. 11 (1): 66–74. PMC 3438153Freely accessible. PMID 22977362. 
  4. ^ Sabbah, H. N.; Stein, P. D. (1981). "Pressure-diameter relations during early diastole in dogs. Incompatibility with the concept of passive left ventricular filling". Circulation Research. 48 (3): 357–65. PMID 7460209. doi:10.1161/01.RES.48.3.357. 
  5. ^ Williams, Gareth. Advanced Biology for You. [page needed][full citation needed]
  6. ^ Erdei T, Aakhus S, Marino P, Paulus WJ, Smiseth OA, Fraser AG (2015). "Pathophysiological rationale and diagnostic targets for diastolic stress testing". Heart (journal). 101 (17): 1355–60. PMID 26001845. doi:10.1136/heartjnl-2014-307040. 
  7. ^ "The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure." (PDF). 
  8. ^ Eroglu, Serpil; Bozbas, Huseyin; Muderrisoglu, Haldun. "Diagnostic value of BNP in diastolic heart failure". Biochemia Medica: 183–192. doi:10.11613/bm.2008.018. 

External links[edit]