FIG. 5.

Impairment of endothelial dysfunction by GTN therapy or traffic noise exposure and improvement by vitamin C coadministration. Left part: Endothelial function was determined by forearm plethysmography, ultrasound-dependent assessment of forearm blood flow in response to increasing doses of infused ACh. FBF was expressed as the ratio of infused to noninfused arm. Each column presents the percent change in FBF from baseline in response to each infused concentration of ACh (7.5, 15, and 30 μg/min) in the untreated control group, chronic GTN treatment for 7 days, and the chronic GTN+vitamin C administration group (Gori et al, 2010). *p < 0.05 versus lowest ACh dose (7.5 μg/min), ^#p < 0.05 versus GTN therapy without vitamin C. Right part: Endothelial function was determined by FMD, ultrasound-dependent assessment of vasodilation (widening) of a large vessel in the arm upon reactive hyperemia after vascular occlusion for 5 min. FMD was determined in subjects without aircraft noise exposure [L_eq 35.4 dB(A)] and 30 or 60 aircraft noise events for 1 night [L_eq 43.1 or 46.3 dB(A)] (Schmidt et al, 2013). Likewise, FMD was determined in subjects without train noise exposure [L_eq 33 dB(A)] and 30 or 60 train noise events for 1 night [L_eq 52 or 54 dB(A)] (Herzog et al, 2019). The effect of vitamin C oral administration on FMD was measured in both the noise exposure studies. *p < 0.05 versus same group without vitamin C, ^†p < 0.05 versus unexposed control group with vitamin C. The schemes in the upper parts were reused from Daiber et al (2017c) with permission. Data in the left part were adapted from Gori et al (2010) (for nitrate tolerance) with permission. Data in the right part were adapted from Herzog et al (2019) and Schmidt et al (2013) (for noise exposure) with permission. FBF, forearm blood flow.