physiology, preload is the pressure stretching the ventricle of the heart, [eMedicineDictionary|ventricular+preload] after atrial contraction and subsequent passive filling of the ventricle. If the chamber is not mentioned, it is usually assumed to be the left ventricle.
Preload is theoretically most accurately described as the initial stretching of a single
cardiac myocyteprior to contraction. This cannot be measured " in vivo" and therefore other measurements are used as estimates. Estimation is inaccurate, for example in a chronically dilated ventricle new sarcomeres may have formed in the heart muscle allowing the relaxed ventricle to appear enlarged. The term end-diastolic volumeis better suited to the clinic, although not exactly equivalent to the laboratory term preload.
Quantitatively, preload can be calculated as
where LVEDP=Left Ventricular end diastolic pressure, LVEDR= Left ventricular end diastolic radius (at the ventricle's midpoint), and h=thickness of the ventricle. This calculation is based on the Law of Laplace.
Factors affecting preload
Preload is affected by venous blood pressure and the rate of venous return. These are affected by venous tone and volume of circulating blood.
Preload relates to the ventricular
end-diastolic volume: a higher end-diastolic volume implies a higher preload, but the relationship is not simple, because of the restriction of the term preload to single myocytes. Single myocytes are not connected simply, but in an interdigitated manner.
Preload increases with exercise (slightly), increasing blood volume (overtransfusion) and excitement (sympathetics).
Frank-Starling law of the heart
* [http://www.cvphysiology.com/Cardiac%20Function/CF007.htm Overview at cvphysiology.com]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Preload — may mean:* Preload (cardiology), a term used in cardiology (the study of the heart) * preload (software), a free Linux program * Preload (engineering), a term used in mechanical engineering to describe the load applied to a fastener merely as a… … Wikipedia
Cardiology — [ ECG indicator; diagrams like this are used in Cardiology.] Cardiology (from Greek gr. καρδίᾱ, kardiā , heart ; and gr. λογία, logia ) is the branch of internal medicine dealing with disorders of the heart and blood vessels. The field is… … Wikipedia
Aortic insufficiency — See also: mitral regurgitation and tricuspid insufficiency Aortic insufficiency Classification and external resources Micrograph of myxomatous degeneration – a cause of aortic insufficiency … Wikipedia
Heart failure — Classification and external resources The major signs and symptoms of heart failure. ICD 10 I5 … Wikipedia
Hypertrophic cardiomyopathy — Classification and external resources ICD 10 I42.1–I42.2 ICD 9 … Wikipedia
Enhanced external counterpulsation — External counterpulsation (ECP) is a procedure performed on individuals with ischemic cardiomyopathy in order to diminish the symptoms of their ischemia. In various studies, ECP has been shown to relieve angina1,2, improve exercise tolerance³,… … Wikipedia
Electrocardiography — ECG redirects here. For other uses, see ECG (disambiguation). Not to be confused with echocardiogram, electromyogram, electroencephalogram, or EEG. Electrocardiography Intervention Image showing a patient connected to the 10 electrodes necessary … Wikipedia
Blood pressure — For information about high blood pressure, see Hypertension. Blood pressure Diagnostics A sphygmomanometer, a device used for measuring arterial pressure. MeSH … Wikipedia
Circulatory system — This article is about the organ system. For the band, see Circulatory System. For transport in plants, see Vascular tissue. Circulatory system … Wikipedia
Nitric oxide — Not to be confused with nitrous oxide or nitrogen oxides. For other uses, see NO (disambiguation). Nitric oxide … Wikipedia