Lovering, AndrewKelly, Tyler2024-03-252024-03-252024-03-25https://hdl.handle.net/1794/29287Patent foramen ovale (PFO) has been documented in humans since Galen reported their existence approximately 2000 years ago. PFO has been associated with a variety of negative outcomes such as impaired ventilatory acclimatization to altitude and increased risk for high altitude pulmonary edema. However, the degree to which PFO impacts pulmonary gas exchange efficiency has remained under debate.Apnea diving presents unique challenges to the cardiopulmonary system. These challenges arise from the combination of physiological stressors created by diving, ranging from increased central venous pressure to severe hypoxia during the final ascent phase a dive. These unique stressors have created unique physiological adaptations in apnea divers. In Chapter IV the interaction of sex and PFO size, as determined by saline contrast echocardiography, is explored in participants at rest and while participating in moderate to strenuous exercise. The data in this chapter show that in females, but not males, with large PFO there is a significant impairment in pulmonary gas exchange efficiency. Additional work in Chapter V shows that percutaneous closure of PFO improves pulmonary gas exchange efficiency in women. Chapter VI examined the prevalence of PFO in apnea divers to non-diving controls, finding that divers are significantly more likely to have a PFO. Chapter VII utilized a 20- to 30-minute hypoxic challenge to investigate changes in pulmonary resistance in divers vs non diving controls. This chapter shows that apnea divers had a severely blunted increase in pulmonary resistance in response to hypoxia. Chapter VIII investigated potential mediators of pulmonary vascular tone in apnea divers and individuals breathing 11.5% oxygen for 7 to 10 hours, as well as whether there were differences in the circulating inflammatory milieu. The data presented in this chapter shows that apnea divers do not have greater bioavailability of nitric oxide nor greater endothelin-1 levels compared to non-diving controls. This dissertation includes previously published co-authored material as well previously unpublished co-authored material.en-USAll Rights Reserved.cardiac physiologyhypoxic pulmonary vasoconstrictionpatent foramen ovalepulmonary hypertensionElectronic Thesis or Dissertation