What physiological need prompts a person to experience orthopnea?

The experience of orthopnea is primarily linked to the need for air while lying down. This condition occurs when a person has difficulty breathing or feels short of breath when they are in a supine position (lying flat) but may not have the same level of discomfort when sitting or standing. The underlying physiological mechanism often involves the redistribution of body fluids when lying down, which can increase venous return to the heart and subsequently elevate pulmonary arterial pressure, leading to pulmonary congestion in individuals with heart failure or other respiratory conditions.

When a person lies flat, the fluid accumulation can impair gas exchange in the lungs, resulting in the sensation of breathlessness. This need for air while in a supine position is what distinguishes orthopnea from other forms of dyspnea. Understanding this physiological need helps identify underlying health issues, such as congestive heart failure, where symptoms are exacerbated while lying down.