Causes of Platypnea
Platypnea is primarily caused by intracardiac shunting, pulmonary arteriovenous malformations, and ventilation-perfusion mismatches that worsen in the upright position and improve when lying down. 1
Definition and Clinical Features
Platypnea is a rare clinical condition characterized by dyspnea that worsens in the upright position and improves when lying down. It is often associated with orthodeoxia, which is a decrease in oxygen saturation when upright. Together, these symptoms constitute platypnea-orthodeoxia syndrome (POS). 1
Major Causes of Platypnea
1. Intracardiac Shunts
- Patent foramen ovale (PFO)
- Atrial septal defects (ASD)
- Fenestrated atrial septal aneurysm
- Right-to-left shunting through intracardiac defects without pulmonary hypertension 2, 3, 4
2. Pulmonary Vascular Abnormalities
- Pulmonary arteriovenous malformations (PAVMs)
- Hepatopulmonary syndrome
- Pulmonary vascular disease 1, 5
3. Ventilation-Perfusion Mismatch
- Chronic obstructive pulmonary disease (COPD)
- Interstitial lung disease
- Pulmonary embolism
- Pneumonia 5
4. Other Causes
- Organophosphorus poisoning (rare but documented cause) 6
- Post-pneumonectomy syndrome
- Severe kyphoscoliosis
- Diaphragmatic paralysis 5
Pathophysiological Mechanisms
The pathophysiology of platypnea varies depending on the underlying cause:
Intracardiac Shunting: In upright position, anatomical changes can occur that direct blood flow through an atrial septal defect or patent foramen ovale, causing right-to-left shunting despite normal pulmonary pressures 3
Pulmonary Arteriovenous Malformations: Gravitational effects in the upright position can increase blood flow through these abnormal vessels, worsening shunting 1
Ventilation-Perfusion Mismatch: In conditions like COPD or interstitial lung disease, the upright position can exacerbate ventilation-perfusion inequality, particularly in basal lung regions 5
Diagnostic Approach
When platypnea is suspected, diagnosis should focus on:
- Confirming positional oxygen desaturation by measuring oxygen saturation in both upright and supine positions
- Identifying the underlying cause through:
- Echocardiography with bubble study to detect intracardiac shunts
- CT angiography to identify pulmonary arteriovenous malformations
- Pulmonary function tests to evaluate for lung disease 1
Clinical Pearls
- Platypnea is often overlooked because standard medical practice involves examining patients in the supine position, which may mask the symptoms 3
- The condition may develop or worsen after pneumonectomy, thoracic trauma, or with advancing age due to anatomical changes 5
- Pregnancy can exacerbate pulmonary arteriovenous malformations due to hormonal and hemodynamic changes 1
Understanding the specific cause of platypnea is crucial for determining appropriate treatment, which may include closure of intracardiac shunts, embolization of pulmonary arteriovenous malformations, or management of underlying pulmonary disease.