system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A 21-year-old man presents to his physician because he has been feeling increasingly tired and short of breath at work. He has previously had these symptoms but cannot recall the diagnosis he was given. Chart review reveals the following results:

Oxygen tension in inspired air = 150 mmHg
Alveolar carbon dioxide tension = 50 mmHg
Arterial oxygen tension = 71 mmHg
Respiratory exchange ratio = 0.80

Diffusion studies reveal normal diffusion distance. The patient is administered 100% oxygen but the patient's blood oxygen concentration does not improve. Which of the following conditions would best explain this patient's findings?
assistant
Septal defect since birth