Impaired brachial artery flow-mediated vasodilation in response to handgrip exercise-induced increases in shear stress in young smokers

Smoking is an established risk factor for cardiovascular disease. It has also been shown to result in endothelial dysfunction as assessed by flow-mediated dilation (FMD) in response to reactive hyperemia (RH)-induced increases in shear stress. Handgrip exercise (HGEX) is an emerging alternative method to increase shear stress for FMD assessment (HGEX-FMD) and the purpose of this study was to identify the impact of smoking on HGEX-FMD in young healthy subjects. Brachial artery RH-FMD and HGEX-FMD (10-minute bout of HGEX) was assessed in eight smokers (S) and 14 non-smokers (NS) (age 21 +/- 2 years). Brachial artery diameter and mean blood velocity were assessed with echo and Doppler ultrasound, respectively. Shear stress was estimated by shear rate (SR = brachial artery blood velocity/diameter). The SR stimulus did not differ between groups for either test (RH-FMD (SR area under the curve until peak diameter measurement), p = 0.897; HGEX-FMD (average SR over 10-minute exercise bout), p = 0.599). The RH-FMD magnitude was not significantly different between groups (S: 7.7 +/- 2.2% vs NS: 7.9 +/- 2.4%, p = 0.838); however, the HGEX-FMD magnitude was significantly impaired in smokers (S: 6.1 +/- 3.4% vs NS: 9.6 +/- 3.6%, p = 0.037). In conclusion, HGEX-FMD assessment detected vascular dysfunction in young healthy smokers while RH-FMD did not. This suggests that HGEX-FMD may be useful in the early detection of smoking-induced impairments in endothelial function. Further research is required to explore this phenomenon in other populations and to isolate underlying mechanisms.