Difficulty breathing when lying flat, requiring the person to sleep propped up on pillows or sitting upright. Commonly associated with heart failure and lung diseases.
From Greek 'orthos' (straight, upright) + 'pnoia' (breathing). The term literally means 'straight breathing' and was coined to describe the need to breathe in an upright position. Ancient physicians noted this pattern but didn't understand the underlying fluid dynamics that cause it.
Orthopnea happens because gravity is both your friend and enemy! When you lie flat, fluid that pools in your legs during the day redistributes to your lungs, making breathing harder - it's like trying to breathe through a wet sponge.
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