Response of retinal blood flow to systemic hyperoxia in smokers and nonsmokers

Background: We investigated the influence of chronic smoking on ocular vascular reactivity during breathing of 100% oxygen. Methods: Retinal vascular reactivity was tested during inhalation of 100% oxygen over 10 min. The observer-masked two-cohort study was performed in 24 healthy male volunteers (12 smokers and 12 nonsmokers) using the Zeiss Retinal Vessel Analyzer and laser Doppler velocimetry. From these parameters retinal blood flow was calculated. Results: Hyperoxia significantly decreased arterial (smokers: p<0.001 vs baseline; nonsmokers: p=0.003 vs baseline) and venous (smokers: p<0.001 vs baseline; nonsmokers: p<0.001 vs baseline) diameters. This decrease was significantly more pronounced in smokers (arterial diameter: p<0.001, venous diameter: p=0.003). Hyperoxia decreased venous blood flow velocity (smokers: p=0.02 vs baseline; nonsmokers: p<0.001 vs baseline) to a comparable degree (p=0.51). The two groups showed a comparable decrease in retinal blood flow during hyperoxia (smokers: p<0.001 vs baseline; nonsmokers: p<0.001 vs baseline; p=0.76 between groups). The decrease of PCO₂ during inhalation of 100% oxygen was significantly more pronounced in smokers than in nonsmokers (p=0.038). Conclusion: The present study indicates a n abnormal retinal vascular response to hyperoxia in smokers. Further studies are needed to identify possible neural or humoral factors involved in this shifted vasoconstrictory status in smokers.