Impaired handgrip exercise-induced brachial artery flow-mediated dilation in young obese males

Flow mediated dilation (FMD) stimulated by different shear stress stimulus profiles may recruit distinct transduction mechanisms, and provide distinct information regarding endothelial function. The purpose of this study was to determine whether obesity influences brachial artery FMD differently depending on the shear stress profile used for FMD assessment. The FMD response to a brief, intermediate, and sustained shear stress profile was assessed in obese (n = 9) and lean (n = 19) young men as follows: brief stimulus, standard reactive hyperemia (RH) following a 5 min forearm occlusion (5 min RH); intermediate stimulus, RH following a 15 min forearm occlusion (15 min RH); sustained stimulus, 10 min of handgrip exercise (HGEX). Brachial artery diameter and mean shear stress were assessed using echo and Doppler ultrasound, respectively, during each FMD test. There was no group difference in HGEX shear stress (p = 0.390); however, the obese group had a lower HGEX-FMD (5.2 ± 3.0% versus 11.5 ± 4.4%, p < 0.001). There was no group difference in 5 min RH-FMD (p = 0.466) or 15 min RH-FMD (p = 0.181); however, the shear stress stimulus was larger in the obese group. After normalization to the stimulus the 15 min RH-FMD (p = 0.002), but not the 5 min RH-FMD (p = 0.118) was lower in the obese group. These data suggest that obesity may have a more pronounced impact on the endothelium's ability to respond to prolonged increases in shear stress.