What causes orthopnea?

Causes of Orthopnea

Orthopnea is most commonly caused by heart failure, which results from increased venous return in the supine position that mobilizes 250-500 cc of fluid from dependent areas to the thoracic compartment, elevating pulmonary capillary pressures and causing interstitial pulmonary edema. 1

Primary Cardiac Causes

Heart failure is the predominant cause of orthopnea, accounting for the majority of cases and demonstrating the highest correlation with elevated pulmonary capillary wedge pressure (PCWP) with sensitivity approaching 90%. 1, 2

Pathophysiological Mechanism in Heart Failure

• When lying flat, venous return increases as fluid shifts from the abdomen and lower extremities to the thoracic compartment, raising right and left-sided filling pressures 1
• This elevated PCWP results in interstitial pulmonary edema, reduced pulmonary compliance, and increased airway resistance 1
• Both systolic heart failure (HF-REF) and diastolic heart failure (HF-PEF) produce orthopnea through this mechanism 2
• Coronary artery disease causes approximately two-thirds of systolic heart failure cases, with hypertension and diabetes as contributing factors 3
• The severity of orthopnea reflects both the absolute PCWP value and the rapidity of its rise 1

Clinical Significance in Heart Failure

• Persistent orthopnea is associated with higher hospitalization rates in heart failure patients 1
• At hospital discharge, heart failure patients should ideally lie flat or with no more than one pillow without developing breathlessness 1
• Treatment with vasodilators and diuretics can abolish supine expiratory flow limitation and control orthopnea in acute left heart failure 4

Pulmonary Causes

Chronic Obstructive Pulmonary Disease (COPD)

• Advanced COPD patients with severe airflow obstruction (FEV1 40% predicted) and lung hyperinflation develop orthopnea through distinct mechanisms from heart failure 5
• In the supine position, COPD patients experience decreased dynamic lung compliance, increased inspiratory work of breathing, and elevated inspiratory neural drive without the compensatory increase in inspiratory capacity seen in healthy individuals 5
• Orthopnea in COPD correlates with increased neuromechanical dissociation and neuroventilatory uncoupling 5

Cardiac Asthma

• "Cardiac asthma" presents with wheezing, coughing, and orthopnea due to reflex bronchoconstriction from pulmonary venous hypertension in congestive heart failure 2
• This condition represents cardiogenic pulmonary edema mimicking primary pulmonary disease 2

Obesity-Related Causes

• Morbidly obese subjects (BMI 51 kg/m²) develop orthopnea through expiratory flow limitation that occurs or worsens in the supine position 6
• The mechanism involves breathing at low lung volume with reduced expiratory reserve volume, promoting expiratory flow limitation when functional residual capacity decreases in recumbency 6
• Orthopnea in obesity is associated with lower seated expiratory reserve volume values and development of supine expiratory flow limitation 6
• Abdominal fat mechanically interferes with lung function due to increased weight on the chest wall, with symptoms worsening when lying down as abdominal pressure pushes up the diaphragm 3

Less Common Causes

Obstructive Sleep Apnea and Obesity Hypoventilation Syndrome

• Obesity hypoventilation syndrome causes shallow, inefficient breathing with patients becoming more symptomatic when lying down due to increased intrathoracic pressure and reduced respiratory capacity 3
• Pickwickian syndrome, a severe form, is associated with extreme obesity, irregular breathing, cyanosis, and right ventricular dysfunction 3

Important Differential: Platypnea-Orthodeoxia Syndrome

• This represents the opposite of orthopnea, where dyspnea and hypoxemia occur in the upright position and improve when lying flat 2, 7
• Caused by intracardiac shunts (such as atrial septal defects) or hepatopulmonary syndrome with pulmonary arteriovenous malformations 2, 7
• The mechanism involves gravity-dependent shunting in lung bases that worsens upright and improves supine 2

Clinical Assessment Approach

• Orthopnea can be objectively tested by having the patient lie supine for 2 minutes while monitoring respiratory rate and breathlessness 1
• The symptom is more specific than general dyspnea but less sensitive, particularly in patients with milder symptoms 3
• Symptoms may be particularly difficult to identify in obese individuals, elderly patients, and those with chronic lung disease 3
• Previous myocardial infarction greatly increases the likelihood of heart failure as the cause 3

Treatment Implications

• Addressing the underlying cause (typically heart failure) is essential for long-term management 1
• Short-term treatment with vasodilators and diuretics can abolish supine expiratory flow limitation and control orthopnea in most patients with acute left heart failure within 7-28 days 4
• ACE inhibitors like lisinopril reduce orthopnea, paroxysmal nocturnal dyspnea, and jugular venous distention when combined with digitalis and diuretics in heart failure patients 8