Clinical Applications
One of the most popular and common functional tests utilizing Transcranial Doppler (TCD) today is the Right-to-Left Shunt (RLS) via the Patent Foramen Ovale (PFO) and follow up after closure-device implantation to evaluate residual RLS and completeness of the closure.
PFO is a type of hole in the heart that “occurs only after birth when the foramen ovale [wall between the right and left atria of every human fetus] fails to close” (American Heart Association). It’s estimated that ~30% of the population (all ages) have PFO. It can cause “venous blood to leak from the right atrium to the left, then out to the body.” This right-to-left shunting of blood may cause serious problems such as low arterial O2 concentration, hypoxia, severely limited exercise capacity, stroke, and migraine.

Apart from cryptogenic stroke, there are other conditions associated with PFO (Fig. 1).



Studies show that the prevalence of PFO in people who suffer from migraine with aura is 50% to 75%, more than twice what would be expected in the general population. Deep Vein Thrombosis (DVT) is caused by disease or lack of activity. DVT is also known as “Economy-Class Syndrome,” as it affects travelers after a long flight. Decompression sickness (DCS) can cause emboli that may reach the brain and cause a stroke. The disorder is most commonly seen in deep-sea divers, astronauts, and high-altitude aviators. In fact, people who suffer from PFO are not allowed to dive.

Rimed’s Digi-Lite TCD

Digi-Lite TCD provides an efficient tool to test PFO due to its high sensitivity and specificity. It’s noninvasive, does not require sedation, and is easily repeatable, making it a safe, comfortable choice for both physicians and patients. To perform the PFO test:

  1. Inject saline containing air bubbles or echo-contrast enhancing agents.
  2. Ask the patient to perform the Valsalva maneuver.
  3. If RLS exists, identify signals of air bubbles in the Middle Cerebral Artery (MCA) on the Doppler Spectrum window.