Does Patent Foramen Ovale Closure Improve Exercise Capacity & Prevent Blood Flow Through Intrapulmonary Shunt

A patent foramen ovale (PFO) is present in ~30% of the general population. The PFO has historically been considered to be trivial. However, recent work by the investigator's group and others has identified that, compared to individuals without a PFO, those with a PFO have a higher core body temperature, significantly worse pulmonary gas exchange efficiency, blunted ventilatory responses to chronic hypoxia and acute carbon dioxide and increased susceptibility to altitude illnesses such as acute mountain sickness, and high altitude pulmonary edema. Specific to this application, subjects with a PFO maybe worse pulmonary gas exchange efficiency because a PFO is a potential source of right-to-left shunt that will make pulmonary gas exchange efficiency worse. If true, then this may negatively impact exercise capacity and/or exercise tolerance.

The investigator's lab group has demonstrated that hypoxemia increases blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) in healthy and subjects with COPD. When these subjects breathe 100% O2 it prevents or reduces blood flow through IPAVA. This suggests that hypoxemia per se induces blood flow through IPAVA. The blood flow through IPAVA and presence of a PFO is also associated with increased risk of stroke and/or transient ischemic attack (TIA). In addition, an atrial septal defect (ASD) is a hole within the interatrial septum, and is considered a congenital heart defect. An ASD is typically larger than a PFO, and thus, the symptoms may be worse in those with an ASD, compared to those with a PFO. Thus, some hypoxemic patients who have had a stroke or transient ischemic attack, who also have a PFO/ASD may undergo surgical closure of their PFO/ASD to prevent subsequent neurological sequelae. This surgical closure may also prevent the hypoxemia thereby reducing or preventing blood flow through IPAVA. Of note, blood flow through IPAVA has been demonstrated to be strongly correlated with TIA and/or stroke and has not previously been taken into consideration in randomized clinical trials mentioned below.

Three randomized clinical trials have determined that PFO closure is not superior to regular medical management, for the prevention of subsequent stroke and/or TIA. Nevertheless, the American Heart Association still recommends that "in patients with cryptogenic [unexplained] TIA or stroke, a PFO, and deep vein thrombosis (DVT), guidelines from the American College of Chest Physicians currently recommend vitamin K antagonist therapy for 3 months and consideration of PFO closure rather than no vitamin K antagonist therapy or aspirin therapy." Additionally, in the largest single center retrospective study performed to date, PFO closure for the purpose of preventing hypoxemia was found to result in "improvement in echocardiographic evidence of right to left shunt, New York Heart Association functional class, and oxygen requirement." Thus, PFO/ASD closure remains a potentially beneficial option for both hypoxemic and stroke/TIA patients.

Lastly, preliminary data also suggest greater levels of plasma inflammatory mediators in subjects with a PFO and systemic inflammation is associated with increased risk of cardiovascular diseases. Importantly, exercise is known to reduce so of these systemic inflammatory mediator levels. Thus, PFO/ASD closure may allow for greater exercise capacity and a subsequent reduction in inflammation.

Thus, although a PFO has been traditionally considered to have a minimal impact of physiology and pathophysiology, emerging evidence suggests this may not be the case. The investigator's lab is focused on understanding how and why a relatively small hole in the heart (PFO/ASD) can have a relatively large impact on cardiopulmonary and respiratory physiology.