Paroxysmal nocturnal dyspnea (PND) is a medical symptom wherein people with congestive heart failure develop difficulties breathing after laying flat. PND commonly occurs several hours after a person with heart failure has fallen asleep. PND resolves quickly once a person awakens and sits upright. It takes longer to develop than orthopnea, which is the inability to lie down flat due to pulmonary fluid accumulation.

PND is caused by increasing amounts of fluid entering the lung during sleep and filling the small, air-filled sacs (alveoli) in the lung responsible for absorbing oxygen from the atmosphere. This fluid typically rests in the legs during the day when the individual is walking around and redistributes throughout the body (including the lungs) when recumbent. PND is a sign of severe heart failure and was first described by Charles Lepois in the 1500s.

Symptoms