Platypnea, derived from Greek platus meaning flat and pnoia meaning breath, is a descriptive term which means shortness of breath that is worsened by being upright (standing or sitting) and improves when lying supine (flat). Shortness of breath when lying supine is called orthopnea.
Different articles have previously described the causes of this condition, but recent review articles have classified the etiology broadly into:
Patent foramen ovale (PFO), atrial septal defect (ASD) and atrial septal aneurysm (ASA) were listed as the most frequent etiologies.
B-Extra-cardiac causes mainly include intra-pulmonary shunts and extra-pulmonary shunts. Pulmonary arteriovenous malformation (AVM), lung parenchymal diseases, and hepato-pulmonary syndrome are examples of pulmonary causes. A few articles described other causes of this condition such as fat embolism, Parkinson disease, among others, but the precise mechanism of those etiologies leading to platypnea remained controversial and elusive.
Burchell et al. first described the condition in 1949, and the term was first used in 1969.
Platypnea may co-exist with or be caused by orthodeoxia which is defined as oxygen desaturation in the upright position. Both constitute a syndrome named platypnea-orthodeoxia syndrome.
No data currently exists to estimate the incidence of platypnea and most cases go undetected unless clinicians specifically ask about the symptoms. Additionally, measuring the degree of dyspnea or the oxygen saturation in the upright and sitting position is not usually part of the routine vital signs measurement or physical examination; hence, positional alterations in oxygenation can be easily overlooked.
The pathophysiology of platypnea is not completely understood, but it appears that the condition occurs in patients with disorders that increase the positional right-to-left shunting through intrapulmonary or intracardiac shunts. This right-to-left shunt could be transient and related to conditions that may worsen right-to-left shunting (like pulmonary hypertension or various other disorders). For example, platypnea may occur in patients with intracardiac right-to-left shunts such as atrial septal defect (ASD) or patent foramen ovale (PFO) after developing a disorder that increases the shunting such as pulmonary hypertension, pulmonary embolism, following a pneumonectomy, or having a large pericardial effusion. Intrapulmonary right-to-left shunts occur mainly in the base of lungs in patients with hepatopulmonary syndrome (HPS). Being in the upright position causes more blood to flow to the lung base, thus aggravating shunting.
Platypnea may also result from worsening ventilation-perfusion mismatch in patients with underlying lung disease especially if the disease is worse at the base of the lung. Many case reports cite such a presentation. For example, patients with idiopathic pulmonary fibrosis may have platypnea-orthodeoxia in the upright position because the fibrosis primarily occurs at the base of the lungs compared to apices.
In the upright position, the blood (perfusion) is directed mainly towards diseased areas resulting in worsening ventilation-perfusion ratio that will improve when lying flat. The same alteration may occur with other lung diseases, such as basilar pneumonia because the disease primarily affects the base of the lung.
Shunt fraction of total cardiac output (Qs/Qt) can be calculated by supplying the patient with 100% oxygen for 20 to 30 minutes then using this equation:
Qs/Qt (Shunt Fraction): (CcO2 - CaO2) / (CcO2 - CvO2)
Where CcO2 is the end capillary O2 content; CaO2 is the oxygen content of the arterial blood, and CvO2 is the oxygen content of the mixed venous blood. In normal people, the shunt fraction is about 5%.
Platypnea is a symptom and not a disease, so once found, a careful history and physical examination should focus on finding the underlying disease that may predispose to it. Some of the findings that one should look for include:
Laboratory tests should be directed to the possible underlying etiology. For example, laboratory studies to evaluate for suspected liver disease.
Echocardiogram with agitated saline bubble study is a very useful initial test to evaluate the presence of intracardiac or extra-cardiac shunts. The appearance of microbubbles in the left atrium during the first 3 beats after opacification of the right chambers suggests an intracardiac shunt whereas the appearance of microbubbles in the left side after more than 3 to 6 beats suggests an extracardiac shunt, for example, an intrapulmonary shunt like in hepatopulmonary syndrome). A Valsalva maneuver may help increase the right-to-left shunting. Other tests to evaluate shunts include a contrast-enhanced echocardiogram, macroaggregated albumin scintigraphy scan, and an invasive angiogram.
Chest plain radiograph may show some underlying lung disease that can explain the platypnea, but this test may not be sensitive.
CT scan in case of suspected lung abnormality may give further details. For example, CT with contrast may show arteriovenous malformations that are causing the right-to-left shunt.
Platypnea is a symptom; therefore, management should be directed toward the underlying disorder. Detailed management of each disease is beyond the scope of this review, but the following measurements apply:
Examples of managing causative disorders include:
The diagnosis of platypnea is usually complex and requires a thorough clinical and radiological assessment of the patient. The clinical outcomes depend on identifying the underlying etiology. Coordination of care and early involvement of an interprofessional team that includes a pulmonologist, cardiologist, radiologist, and a respiratory therapist is essential for early diagnosis and targeted treatment. Ideally, the underlying disorder will be treated, thus eliminating the respiratory symptoms. If this is not possible due to the nature of the underlying disorder, clinical management of platypnea must target patient education and symptom management.
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