In a multiple regression model, impaired CO2R was independently associated with an
increased risk of ipsilateral ischemic stroke (hazard ratio [HR] 3.69; confidence interval [CI]
2.01, 6.77; p , 0.0001). Risk prediction was similar for recently symptomatic vs asymptomatic
patients. Using continuous values of pCi, a significant association between decreasing pCi and
increasing risk of ipsilateral stroke was found: HR of 1.64 (95% CI 1.33, 2.02; p , 0.0001) per
10% decrease in pCi. For patients with asymptomatic internal carotid artery stenosis only (n 5
330), a comparable stroke risk prediction was found: increasing HR 1.95 (95% CI 1.26, 3.04;
p 5 0.003) per 10% decrease in pCi.