What mechanical factor contributes to PCS?

The correct answer highlights the role of venous valves in the venous system and how their absence can lead to Postural Changes Syndrome (PCS). Venous valves are critical in maintaining unidirectional blood flow back to the heart. When these valves are absent or dysfunctional, it can lead to venous reflux, where blood flows backward in the veins, causing increased venous pressure, pooling of blood, and ultimately contributing to symptoms associated with PCS.

This absence can significantly affect the patient’s capacity to manage the blood flow within the lower extremities, especially during activities such as standing or walking. In contrast, the other factors like the presence of uterine fibroids, excessive exercise, and severe obesity, while they may influence overall venous health and contribute to other venous or vascular issues, do not directly relate to the fundamental mechanical aspects of valve function that are a crucial part of PCS. Thus, the primary mechanical factor defining PCS focuses effectively on the absence of venous valves.