What causes fluid buildup in lower extremities in right-sided heart failure?

In right-sided heart failure, the primary mechanism leading to fluid buildup in the lower extremities is the backflow of blood into systemic circulation.

When the right side of the heart fails to pump blood effectively, the blood returning from the body can accumulate, leading to increased venous pressure. This elevated pressure in the venous system causes fluid to leak out of the capillaries and into the interstitial spaces of the tissues, particularly in the lower extremities. This condition is commonly referred to as peripheral edema. The heart's inability to manage the volume of blood returning from the systemic circulation results in congestion, which manifests as swelling in the legs and feet.

Other factors, such as decreased cardiac output, certainly play a role in heart failure, but it is the direct effect of the backflow and congestion resulting from right-sided heart function that specifically leads to the fluid accumulation in the lower extremities. Increased lung pressure is more associated with left-sided heart failure and its effects, while increased systemic vascular resistance can affect heart function but doesn't directly cause fluid buildup in the way indicated in this scenario.