A bubble study is often utilized to confirm the presence of shunting across the interatrial septum (IAS) via patent foramen ovale (PFO) or atrial septal defect (ASD). This study is combined with color flow doppler and 2D inspection of the IAS anatomy to determine if there indeed is a defect.
A Valsalva maneuver increases intrathoracic pressure and compresses the compliant, low-pressure superior and inferior vena cavas. This, in turn, transiently reduces blood return to the right atrium (RA) creating low right atrial pressure. Once the Valsalva is relieved, blood rushes back into the RA, quickly increasing right atrial pressure. This should cause the IAS to bow into the left atrium (LA) and “force” a shunt to become right-to-left.
Because of the left-sided continuous suction from a left ventricular assist device (LVAD), it’s important to identify and close any PFO or ASD to prevent right-to-left shunting and resulting hypoxemia.
Here’s an example of a normal bubble study. Note the RA fills with bubbles, but there are no immediate bubbles in the LA.
Now here’s an example of a “positive” bubble study where bubbles are immediately seen in the LA