Control of cardiac output

Cardiac output dependent on

• Heart rate
• Contractility
• Preload
• Afterload

Note:

• Contractility and heart rate are strictly cardiac factors
• Preload and afterload depends on both vascular and cardiac factors

Cardiac function curve

Shows how changes in right atrial pressure affects cardiac output

Vascular function curve

Shows how changes in cardiac output affects right atrial pressure

Note:

• For vascular function curve, the axis are swapped so that the dependent variable (RAP) is on the x-axis.

Equilibrium

Interaction of cardiac function curve and vascular function curve shows
--> the equilibrium cardiac output at a particular level of right atrial pressure (or central venous pressure)

In normal person, at equilibrium,

• Cardiac output = 5L/min
• Right atrial pressure = 2mmHg

Heart rate

In most cases (in normal persons)

When HR is between 100-200 [BL8:p217]

Changes in heart rate

--> Changes in preload, afterload, and contractility

--> Cardiac output is not changed significantly

Other notes

• Central venous pressure = 4.6mmHg average
  [WG21:p597]
• Antecubital vein pressure = 7.1mmHg
  [WG21:p598]