Effect of body position and oxygen tension on foramen ovale recruitment.
While there is an increased prevalence of stroke at altitude in individuals who are considered to be low risk for thrombotic events, it is uncertain how venous thrombi reach the brain. The patent foramen ovale (PFO) is a recruitable intracardiac shunt between the right and left atrium. We aimed to determine whether body position and oxygen tension affect blood flow through the PFO in healthy adults. We hypothesized that hypoxia and body positions that promote right atrial filling would independently recruit the PFO. Subjects with a PFO (n = 11) performed 11 trials, combining four different fractions of inhaled oxygen (FiO₂) (1.0, 0.21, 0.15, and 0.10) and three positions (upright, supine, and 45° head down), with the exception of FiO₂ = 0.10, while 45° head down. After 5 min in each position, breathing the prescribed oxygen tension, saline bubbles were injected into an antecubital vein and a four-chamber echocardiogram was obtained to evaluate PFO recruitment. We observed a high incidence of PFO recruitment in all conditions, with increased recruitment in response to severe hypoxia and some contribution of body position at moderate levels of hypoxia. We suspect that increased pulmonary vascular pressure, secondary to hypoxia-induced pulmonary vasoconstriction, increased right atrial pressure enough to recruit the PFO. Additionally, we hypothesize that the minor increase in breathing resistance that was added by the mouthpiece, used during experimental trials, affected intrathoracic pressure and venous return sufficiently to recruit the PFO.
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin; Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin;
Kayla L
KL
Moses
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin;
Arij G
AG
Beshish
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin;
Nicole
N
Heinowski
Adult Echocardiography Laboratory, University of Wisconsin Hospital and Clinics, Madison, Wisconsin; and.
Kim R
KR
Baker
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin;
David F
DF
Pegelow
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin; Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin; Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin;
Marlowe W
MW
Eldridge
Department of Pediatrics, Critical Care Division, and the John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin; Department of Health and Human Physiology, University of Iowa, Iowa City, Iowa melissa-bates@uiowa.edu.
Melissa L
ML
Bates
D000293:Adolescent; D000328:Adult; D000531:Altitude; D062186:Arterial Pressure; D016280:Atrial Function, Right; D015415:Biomarkers / Q000097:blood; D003287:Contrast Media / Q000008:administration & dosage; D004452:Echocardiography; D005260:Female; D054092:Foramen Ovale, Patent / Q000097:blood / Q000150:complications* / Q000000981:diagnostic imaging / Q000503:physiopathology; D018475:Head-Down Tilt; D006439:Hemodynamics; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000150:complications* / Q000503:physiopathology; D007275:Injections, Intravenous; D008297:Male; D010100:Oxygen / Q000097:blood*; D011187:Posture; D011651:Pulmonary Artery / Q000503:physiopathology; D011652:Pulmonary Circulation; D012720:Severity of Illness Index; D012965:Sodium Chloride / Q000008:administration & dosage; D020521:Stroke / Q000209:etiology / Q000503:physiopathology; D016683:Supine Position; D013997:Time Factors; D014655:Vascular Resistance; D014661:Vasoconstriction; D055815:Young Adult
D015415:Biomarkers; D003287:Contrast Media; D012965:Sodium Chloride; D010100:Oxygen
airway resistance; altitude; hypoxia; patent foramen ovale; stroke