Nitin M. Apte, MD; Dilip R. Karnad, MD
To the Editor: Dillard and colleagues (1) have described three equations that predict arterial oxygen tension (PaO2) at 8000 feet, which is the lowest cabin pressure permitted in commercial aircraft. They claim that addition of FEV1, m either litres or percent, to preflight PaO2 accurately predicts PaO2 at 8000 feet and may identify patients with chronic obstructive pulmonary disease needing inflight oxygen therapy.
For a given ventilation-perfusion relation, the ratio of arterial PO2 to alveolar PO2 (PAO2) is constant over a wide range of oxygen concentrations in inspired air (2). It is, therefore, reasonable to assume that PaO2G/PAO2G = PaO2Alt/PAO2Alt
Nitin M. Apte, Dilip R. Karnad. Altitude Hypoxemia and the Arterial-to-Alveolar Oxygen Ratio. Ann Intern Med. 1990;112:547–548. doi: 10.7326/0003-4819-112-7-547
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Published: Ann Intern Med. 1990;112(7):547-548.
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