Cardiac function curve

An article about the cardiac function curve in cardiovascular physiology

Cardiac Function Curve

The cardiac function curve is a graphical representation of the relationship between the right atrial pressure (RAP) and the cardiac output (CO). It is an essential concept in cardiovascular physiology that helps in understanding how the heart responds to changes in venous return and other physiological conditions.

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A typical cardiac function curve showing the relationship between right atrial pressure and cardiac output.

Physiological Basis

The cardiac function curve is based on the Frank-Starling law of the heart, which states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume), when all other factors remain constant. This relationship is due to the intrinsic property of cardiac muscle fibers to contract more forcefully when they are stretched to a greater length.

Components of the Curve

The cardiac function curve typically has a positive slope, indicating that as the right atrial pressure increases, the cardiac output also increases. This is because increased right atrial pressure reflects increased venous return, leading to greater end diastolic volume and thus greater stroke volume.

Plateau Phase

At higher levels of right atrial pressure, the curve may plateau, indicating that further increases in venous return do not lead to significant increases in cardiac output. This plateau occurs because the heart reaches its maximum capacity to pump blood effectively.

Factors Affecting the Curve

Several factors can shift the cardiac function curve:

• Inotropic State: Positive inotropic agents, such as catecholamines, can shift the curve upward, indicating increased cardiac output at any given right atrial pressure. Conversely, negative inotropic agents can shift the curve downward.
• Heart Rate: Changes in heart rate can also affect the position of the curve. An increase in heart rate can increase cardiac output, shifting the curve upward.
• Afterload: Increased afterload, or resistance against which the heart must pump, can shift the curve downward, as the heart must work harder to eject blood.

Clinical Implications

Understanding the cardiac function curve is crucial in clinical settings, particularly in managing conditions such as heart failure, where the heart's ability to pump blood is compromised. Therapeutic interventions often aim to optimize the position of the cardiac function curve to improve cardiac output and patient outcomes.

Related Pages

• Frank-Starling law of the heart
• Cardiac output
• Venous return
• Heart failure
• Inotropic agents