The foramen ovale which is part of the normal fetal cardiopulmonary circulation, fails to close after birth in ~35% of the population and represents a source of right-to-left shunt. Despite the prevalence of patent foramen ovale (PFO) in the general population, cardiopulmonary, exercise, thermoregulatory and altitude physiologists have underestimated the potential effect of this shunted blood flow on normal physiological processes in otherwise healthy humans. Since this shunted blood bypasses the respiratory system, it does not participate in either gas exchange or respiratory system cooling and may have impacts on other physiological processes that remain undetermined. The consequences of this shunted blood flow in PFO positive (PFO+) subjects can have a significant, and negative, impact on the alveolar-to-arterial oxygen difference (AaDO2), ventilatory acclimatization to high altitude and respiratory system cooling with PFO+ subjects having a wider AaDO2 at rest and during exercise, blunted ventilatory acclimatization and a higher core body temperature (~0.4°C) at rest and during exercise. There is also an association of PFO with high altitude illnesses. Furthermore, these effects on physiological processes are dependent on the presence and size of the PFO such that subjects with small PFOs do not appear to be significantly different from subjects without PFO. The PFO can be a physiologically important determinant of normal physiological processes and should be considered a potential confounder to the interpretation of former and future data sets, particularly in small data sets where a significant number of PFO+ subjects could be present and may significantly impact the data.
Andrew Lovering earned a B.S. in Biology from Texas Tech University in 1995. He received his Ph.D. in physiology from Texas Tech University School of Medicine in 2003. He was a postdoctoral fellow in the Rankin Laboratory of Pulmonary Medicine (University of Wisconsin School of Medicine and Public Health) before he joined the Department of Human Physiology at the University of Oregon in 2007. Dr. Lovering has a long-standing interest in pulmonary gas exchange efficiency and began his interest in the patent foramen ovale after he became tired of screening out otherwise healthy subjects from his studies. The patent foramen ovale allows blood to bypass the lungs and therefore represents a source of shunt. Our investigations have found that this seemingly small hole in the heart has a rather significant impact on more than just pulmonary gas exchange efficiency.
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