Cardiac function curve

Cardiac function curve

A cardiac function curve is a graph showing the relationship between right atrial pressure (x-axis) and cardiac output (y-axis).

Shape of curve

It shows a steep relationship at relatively low filling pressures and a plateau, where further stretch is not possible and so increases in pressure have little effect on output. The pressures where there is a steep relationship lie within the normal range of right atrial pressure (RAP) found in the healthy human during life. This range is about -1 to +2 mmHg. The higher pressures normally occur only in disease, in conditions such as heart failure, where the heart is unable to pump forward all the blood returning to it and so the pressure builds up in the right atrium and the great veins. Swollen neck veins are often an indicator of this type of heart failure.

At low right atrial pressures this graph serves as a graphic demonstration of the Frank-Starling mechanism, that is as more blood is returned to the heart, more blood is pumped from it without extrinsic signals.

Changes in the cardiac function curve

In vivo however, extrinsic factors such as an increase in activity of the sympathetic nerves, and a decrease in vagal tone cause the heart to beat more frequently and more forcefully. This alters the cardiac function curve, shifting it upwards. This allows the heart to cope with the required cardiac output at a relatively low right atrial pressure. We get what is known as a family of cardiac function curves, as the heart rate increases before the plateau is reached, and without the RAP having to rise dramatically to stretch the heart more and get the Starling effect.

In vivo sympathetic outflow within the myocardium is probably best described by the time honored description of the sinoatrial tree branching out to Purkinges fibers. Parasympathetic inflow within the myocardium is probably best described by influence of the vagus nerve and spinal accessory ganglia.


Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • cardiac output curve — a graphic representation of cardiac output as a function of atrial pressure; it is a measure of the pumping ability of the heart under specific conditions. See also Starling c. and venous return c …   Medical dictionary

  • Cardiac output — (Q or or CO ) is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min (1 dm3 equals 1000 cm3 or 1 litre). Q is… …   Wikipedia

  • Cardiac cycle — Cardiac events occurring in the cardiac cycle. Two complete cycles are illustrated. The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the… …   Wikipedia

  • curve — 1. A nonangular continuous bend or line. 2. A chart or graphic representation, by means of a continuous line connecting individual observations, of the course of a physiologic activity, of the number of cases of a disease in a given period, or of …   Medical dictionary

  • Starling curve — a graphic representation of cardiac output, or other measure of ventricular performance, as a function of ventricular filling for a given level of contractility; as atrial pressure and venous return increase, cardiac output initially increases… …   Medical dictionary

  • venous return curve — a graphic representation of venous return as a function of atrial pressure; it measures the contributions of peripheral factors that affect the flow of blood from the veins to the heart. Multiple curves generated under varying conditions are… …   Medical dictionary

  • dye dilution curve — an indicator dilution curve in which the indicator is a dye, usually indocyanine green; it is used in studies of cardiac output and other aspects of cardiovascular function …   Medical dictionary

  • 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

  • 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

  • Multifunction cardiogram — Multifunction CardioGramTM (MCGTM) is an FDA and AMA approved diagnostic tool used to diagnose myocardial ischemia due to Coronary Artery Disease (CAD). MCG records resting ECG data between the Myocardium and intra cardiac blood flow to… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”