4 Preload and Afterload Free Online FlashCards

What is preload?

Preload is the stretch of ventricular muscle at the end of diastole, just before contraction.

Why is filling pressure not identical to preload?

Preload is related to end-diastolic volume, but it is not identical to a filling-pressure reading; ventricular size, stiffness, and surrounding pressure affect their relationship.

How can hemorrhage or dehydration affect preload?

Hemorrhage and dehydration can reduce venous return and preload by lowering circulating blood volume.

What does the Frank–Starling mechanism describe?

Through the Frank–Starling mechanism, greater filling usually increases contraction force and stroke volume within the heart’s physiologic range.

Why might extra fluid fail to improve output?

The response has limits: a failing or already overfilled ventricle may gain little output from extra fluid, while excess filling can worsen congestion or pulmonary edema.

What is afterload?

Afterload is the load a ventricle must overcome to eject blood.

What influences left-ventricular afterload?

Left-ventricular afterload is influenced by aortic pressure, systemic vascular resistance, and the properties of the aorta.

How can increased afterload affect stroke volume?

Hypertension, vasoconstriction, and aortic stenosis can increase left-ventricular afterload. Increased afterload can reduce stroke volume, especially if contractility is impaired.

Are blood pressure and systemic vascular resistance direct measures of afterload?

Blood pressure and systemic vascular resistance are useful clues, not direct measurements of ventricular afterload; ventricular geometry and wall stress also matter.

How is cardiac output calculated?

Cardiac output is heart rate multiplied by stroke volume: $\mathrm{CO} = \mathrm{HR} \times \mathrm{SV}$.

Can CVP or PAOP alone establish preload or predict fluid responsiveness?

No. CVP and PAOP are not reliable standalone measures of preload or predictors of fluid responsiveness; their interpretation is affected by factors such as ventilation, chest pressure, and ventricular compliance.

What does a passive leg raise test help determine?

A passive leg raise with stroke volume or cardiac output measurement tests whether a reversible increase in venous return meaningfully improves output. Responsiveness alone does not prove that fluid is safe or necessary.