orthopnea
Orthopnea is breathlessness that appears when a person lies flat and eases when they sit upright or stand. The classic giveaway is the patient who needs two or three pillows to sleep, or who ends up sleeping in an armchair, because lying down makes breathing feel impossible.
Lying flat shifts blood from the legs and abdomen back toward the chest, raising the volume the heart and lungs must handle. In someone whose heart is failing, the left side cannot move this extra return forward fast enough, so pressure backs up into the lung vessels and fluid seeps toward the air spaces, stiffening the lungs and triggering breathlessness. Sitting up lets gravity pool blood lower again and drops the diaphragm, relieving the sensation within minutes.
Although orthopnea is a hallmark of left heart failure, it is not unique to it. Severe lung disease, large pleural effusions, marked obesity, and diaphragm weakness can all make lying flat uncomfortable. Counting the number of pillows used, sometimes called pillow orthopnea, gives a rough, trackable measure of severity over time.
A man with heart failure mentions he has been sleeping propped on three pillows for a month; flat on the examination couch he becomes short of breath within a minute and asks to sit up.
Counting pillows is a simple bedside way to gauge orthopnea and follow a patient's congestion.
Orthopnea relieves quickly on sitting up, which distinguishes it from paroxysmal nocturnal dyspnea, where the breathlessness wakes the person abruptly and takes longer to settle.