Which of the following is a possible cause of orthostatic hypotension?

Orthostatic hypotension occurs when there is a significant drop in blood pressure upon standing up from a sitting or lying position. One of the primary causes of this condition is decreased cardiac output.

When a person stands up, gravity causes blood to pool in the lower extremities. Normally, the body compensates for this by increasing heart rate and constricting blood vessels to maintain blood pressure and ensure adequate blood flow to vital organs. However, if there is a decrease in cardiac output—due to factors such as reduced heart function, volume loss from dehydration, or blood loss—the body may not be able to effectively compensate for this change in position. As a result, the person may experience dizziness, lightheadedness, or fainting, which are symptoms associated with orthostatic hypotension.

The other options focus on mechanisms that typically promote or stabilize blood pressure rather than contribute to a drop in it when changing positions. Increased oncotic pressure, increased systemic vascular resistance, and decreased hydrostatic pressure would not lead to the same effect of reduced blood flow when standing, thereby making decreased cardiac output the most relevant answer in this scenario.