The Effect of a Patent Foramen Ovale on the Hypoxic Ventilatory Response
Chang, Alex J.
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Chang, Alex J.
Approximately 25-40% of the general healthy population has a patent foramen ovale (PFO) (Woods et al., 2010; Marriott et al., 2013; Elliott et al., 2013). Previous work by our lab has shown that after 16 days of exposure to 5260 m, subjects with a PFO (PFO+) had blunted ventilatory acclimatization to high altitude compared to subjects without a PFO (PFO–), such that PFO+ subjects had a lower partial pressure of arterial O2, higher partial pressure of arterial CO2, and lower O2 saturation (Elliott et al., 2015). However, in that study 7 / 11 PFO+ subjects were female, whereas only 2 / 10 PFO- subjects were female and thus potential sex differences were not accounted for and it is known that sex hormones can affect ventilatory responses to O2 and CO2 (Schoene et al., 1986; Slatkovska et al., 2006). Thus, it remains unknown if PFO+ subjects exhibit blunted acute ventilatory responses to hypoxia compared to PFO– subjects, independent of sex. Therefore, the purpose of this study was to determine if the presence of a PFO affects ventilatory responses during acute exposure to either poikilocapnic hypoxia or isocapnic hypoxia A total of 31 healthy, non-smoking subjects matched for height, weight, sex and age completed the entire study PFO+: age: 24 ± 5 yrs, height: 170 ± 11 cm, weight: 69 ± 14 kg, BSA: 1.8 ± 0.2 m2 PFO-: age: 27 ± 9 yrs, height: 172 ± 10 cm, weight: 71 ± 16 kg, BSA: 1.8 ± 0.2 m2 These 31 subjects included 15 PFO+ subjects (8 female) and 16 PFO – subjects (9 female). Subjects came to the lab and participated in two trials: poikilocapnic hypoxia (PH) and isocapnic hypoxia (IH). These trials were administered using the Dynamic End-tidal Forcing (DEF) breathing response system in a randomized and balanced order. The subjects were given a 40 min break between hypoxia trials. Acute Hypoxic ventilatory response (AHVR), calculated as the change in VE divided by the change in SpO2 (∆VE/ ∆ SpO2), was done for both PH and IH trials. Hypoxic ventilatory decline (HVD), calculated as a percent decline with respect to the initial increase in VE, was performed for IH trials only Despite differences in ventilatory acclimatization to high altitude, there were no difference in AHVR between PFO+ and PFO- subjects. PFO+ and PFO- showed no significant differences in hypoxic ventilatory decline HVD. There were also no differences in AHVR and HVD between males and females. Thus, our findings suggest differences in ventilatory acclimatization with chronic exposure to high altitude are likely not due to baseline differences in hypoxic chemosensitivity.