Active pulmonary hypertension can be caused by which of the following?

Active pulmonary hypertension involves an increase in blood pressure within the pulmonary arteries, and this can be triggered by various factors. Constriction of the pulmonary circuit directly contributes to elevated pressures in this vascular system. When the smooth muscle in the pulmonary arteries contracts, it narrows the diameter of these blood vessels, leading to increased resistance against which the heart has to pump. As a result, this heightened resistance raises pulmonary pressures, thereby establishing conditions for pulmonary hypertension.

This physiological mechanism is fundamental for understanding how different pathologies can lead to active pulmonary hypertension. For instance, primary pulmonary hypertension is often associated with intrinsic vasoconstriction processes that can be exacerbated by other conditions like hypoxia or increased blood viscosity. Recognizing the role of vascular constriction in the pathophysiology of pulmonary hypertension is crucial for diagnosing and managing the condition effectively.

Other factors such as excessive fluid retention, thromboembolic disease, and infectious processes do have associations with pulmonary hypertension but through different mechanisms, typically involving fluid load or obstruction rather than active constriction of the existing pulmonary circuit itself. Thus, understanding the specific nature of the pulmonary circuit's constriction provides better insight into the dynamics of active pulmonary hypertension.