PLATYPNEA and ORTHODEOXIAAfter discussing an approach to dyspnea on exertion, the symptom of platypnea was discussed.
Platypnea is an increase in dyspnea in the upright position that improves on lying down.
Orthodeoxia is a decrease in oxygen saturation that occurs upon rising from supine.
These often occur together. They happen when there is right to left shunting that only occurs or is more pronounced, in the upright position. Shunts can be intracardiac (ASD, PFO) or intrapulmnary (AVM, hepatopulmonary syndrome).
This often occurs in HHT, when larger pulmonary AVMs are in bases of the bases of the lungs and therefore recevie a greater proportion of blood when the patient is upright. It can also occur for anatomic reasons in patients with intracardiac shunts.
Shunting can be seen with contrast ECHO where agitated saline bubbles are injected into peripheral veins. They appera in the right heart, and if a right to left shunt exists then they will appear in the left side of the heart. If they appear in 1-2 beats, the shunt is intracaridac, in 3-8 beats then it is likely intrapulmonmary.
Shunt fraction can be calculated by testing SaO2 and PaO2 before and after breating 100% oxygen fro 15 minutes. Normal is less than 5%.
International guidelines for the diagnosis and management of HHT (published by Toronto clinicians) can be found here.
A NEJM review of HHT can be found here.
A NEJM review of hepatopulmonary syndrome can be found here.
