What condition is indicated by orthopnea?

Orthopnea is a condition characterized by difficulty breathing when lying flat, leading individuals to find relief in an upright position. This condition often indicates that a person may have heart or respiratory issues, where fluid accumulates in the lungs when lying down.

In contrast to the other options, breathing difficulties associated with orthopnea specifically improve when a person is sitting or standing, which is not adequately described by the other choices. Thus, the correct understanding of orthopnea is that it is the inability to breathe comfortably except in an upright position, making option C the accurate reflection of this condition.