The effect of acute hypoxemia on coronary arterial dimensions in patients with coronary artery disease

Objectives: To assess the influence of acute hypoxemia on the dimensions of diseased and nondiseased coronary arterial segments in humans. Methods: In 18 subjects (age 53 ± 8 years) with known or suspected coronary artery disease, quantitative coronary angiography was performed before and after being randomly assigned to breathing (1) an inspired oxygen concentration (fraction of inspired oxygen, FIO₂) of 21% (room air, RA) for 20 min (n = 4, controls) or (2) an FIO₂ of 15 and 10% for 10 min each (corresponding to altitudes of 2,500 and 5,500 m, respectively; n = 14). Results: In the control subjects, no hemodynamic, oximetric or angiographic variable changed. In the 14 study subjects, the arterial partial pressure of oxygen averaged 85 ± 13 mm Hg on RA, 65 ± 15 mm Hg on 15% FIO₂ and 44 ± 13 mm Hg on 10% FIO₂. Average arterial segment diameter was 2.52 ± 0.63 mm on RA, 2.55 ± 0.62 mm on 15% FIO₂ (not significant vs. RA) and 2.66 ± 0.66 mm on 10% FIO₂ (p < 0.001 vs. RA). The increase in coronary arterial diameter with 10% FIO ₂ occurred only in normal segments (2.74 ± 0.64 vs. 2.97 ± 0.64 mm; p < 0.001), but not in diseased segments (2.34 ± 0.57 vs. 2.38 ± 0.55 mm; not significant). Conclusions: In humans, severe hypoxemia induces vasodilation of angiographically normal coronary arterial segments, whereas it causes no change in diseased segments.