Recent studies suggest that smokers' coronary endothelial function is impaired because of increased oxidative stress, and their coronary flow velocity reserve (CFVR) is reduced. It is uncertain whether oral antioxidant vitamin C restores impaired CFVR in smokers. Recent technological advances in transthoracic Doppler echocardiography (TTDE) have resulted in the successful measurement of coronary flow velocity and noninvasive CFVR assessment.

We studied 13 healthy young male smokers and 12 nonsmokers. Coronary flow velocities in the left anterior descending coronary artery (LAD) were recorded with TTDE at rest and during hyperemia induced with intravenous infusion of adenosine triphosphate (ATP). CFVR was calculated as the ratio of hyperemic to basal mean diastolic flow velocity. CFVR and plasma concentrations of vitamin C were assessed at baseline and 2 and 4 hours after oral intake (2 g).

Heart rate and blood pressure responses to ATP infusion were not affected by oral vitamin C, but plasma concentrations of vitamin C increased to physiological levels in both groups. CFVR was significantly higher in nonsmokers than in smokers at baseline (4.3 ± 0.4 vs 3.8 ± 0.8, P <.05). After oral vitamin C, it was increased significantly in smokers (3.8 ± 0.8 to 4.5 ± 0.7, P <.005, 4.5 ± 0.8, P <.005, respectively), but not in nonsmokers (4.3 ± 0.4 to 4.3 ± 0.3, 4.4 ± 0.7).

This study demonstrated that oral vitamin C restores coronary microcirculatory function and impaired CFVR against oxidative stress in smokers.