Cardiac Function Curve - Shape of Curve

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.