Understanding Orthopnea and Its Causes

Orthopnea occurs when lying flat increases venous return to the heart and redistributes blood from the lower extremities to the central circulation, leading to increased pulmonary venous pressure and pulmonary congestion, as explained by the American Thoracic Society 1
Elevated pulmonary venous pressure from left-sided cardiac disease directly causes orthopnea, according to the American College of Cardiology 2

Heart Failure and Orthopnea

Congestive heart failure is a cause of orthopnea due to pulmonary edema and pulmonary vascular congestion, with both systolic and diastolic heart failure producing orthopnea, as stated by the American Heart Association 1, 3
The sensation of "air hunger" and "inability to get a deep breath" characterizes heart failure due to increased respiratory drive and limited tidal volume, as described by the American Thoracic Society 1

"Cardiac asthma" presents with wheezing, coughing, and orthopnea due to congestive heart failure, representing reflex bronchoconstriction from pulmonary venous hypertension, as explained by the American Academy of Allergy, Asthma, and Immunology 4

Hepatopulmonary syndrome involves pulmonary arteriovenous malformations and right-to-left shunts causing hypoxemia, with patients characteristically experiencing platypnea and orthodeoxia, which is the opposite of orthopnea, as described by the American Association for the Study of Liver Diseases 4, 5
The mechanism involves gravity-dependent shunting in the lung bases that worsens in the upright position and improves when lying flat, as explained by the American Thoracic Society 4, 5

Left-sided valvular disease, such as mitral stenosis, mitral regurgitation, and aortic regurgitation, elevates pulmonary venous pressure, according to the American College of Radiology 6

Dynamic hyperinflation worsens in the supine position due to altered diaphragm mechanics in patients with Chronic Obstructive Pulmonary Disease (COPD), as reported by the American College of Radiology 7

Bilateral diaphragm paralysis causes severe orthopnea as the supine position eliminates gravitational assistance to breathing, as noted by the American College of Radiology 8, 9
Paradoxical abdominal motion is a sign of diaphragm dysfunction when supine, according to the American College of Radiology 9

Initial evaluation should include looking for distended jugular veins, S3 heart sound, peripheral edema, pulmonary crackles, and paradoxical abdominal motion, as recommended by the American College of Radiology 6, 9
Chest radiograph is a first-line test to identify pulmonary edema, pleural effusion, or cardiomegaly, as suggested by the American College of Radiology 7, 9
Electrocardiogram is a first-line test for cardiac abnormalities, according to the American College of Radiology 7
Spirometry with supine and upright measurements can detect diaphragm dysfunction, with a >20% FVC drop when supine suggesting diaphragm paralysis, as reported by the American College of Radiology 8