Perfusion-Cardiac Function Concepts

Vascular

Resistance (SVR)

The resistance the heart must overcome to pump blood through vessels

What does SVR affect?

Vessel Diameter

Blood Viscosity

SNS Stimulation

Stroke Volume

(SV)

Amount of blood ejected from left ventricle per beat (Normal ~60–100 mL)

What does SV affect?

Preload

afterload

contractility

Cardiac Output

(CO)

Amount of blood pumped per minute

What does Cardiac Output affect?

HR

SV

Cardiac Output Equation?

CO = HR x SV

Preload

Amount of stretch in ventricles at end of diastole

(volume filling the heart)

What affects Preload?

Blood Volume

Venous Return

Afterload

Resistance the ventricle must overcome to eject blood

What effects Afterload?

SVR

hypertension

aortic stenosis

Ejection Fraction (EF)

Percentage of blood ejected from LV per beat (Normal ≥55–65%)

What effects EF?

Contractility

heart damage

Contractility

Strength of ventricular contraction independent of preload

What affects Contractility?

SNS stimulation

oxygen supply

medications

Starling’s Law of the Heart

The more the heart muscle stretches during filling, the stronger the contraction (to a limit)

Self-Excitation (Automaticity)

Ability of cardiac cells to generate electrical impulses without external stimulation

What affects Automaticity?

SA node function

electrolytes

ischemia