Pulse wave amplitude is associated with brachial artery diameter: Implications for gender differences in microvascular function

The ratio of pulse wave amplitude (PWA) during reactive hyperemia compared to baseline as measured by peripheral arterial tonometry (PAT) is a non-invasive measure of microvascular endothelial function referred to as the pulse wave amplitude reactive hyperemia index (PWA-RHI). Whether upstream conduit vessel structure may affect downstream resistance vessel PWA has not been clearly examined. We tested the hypothesis that digital PWA is influenced by brachial artery diameter (BAD) and that this association would influence comparison of PWA-RHI between genders. Measures of vascular structure and microvascular function were carried out in 115 patients varying in cardiovascular risk profiles (average age 57 years, male n = 79, CAD n = 43). PWA was assessed using plethysmography at baseline and following 5 minutes of brachial artery occlusion. BAD was assessed using high-resolution ultrasonography. Results : There was a negative association between BAD and PWA-RHI ( r = -0.34, p < 0.05). Women had greater PWA-RHI and smaller BAD compared with men (p < 0.05). When co-varying for BAD, there were no longer gender differences in PWA-RHI. Moreover, when a sub-group of men and women without CAD (n = 40), matched for BAD, were examined, there were no gender differences in PWA-RHI. In conclusion, PWA-RHI obtained from PAT is associated with BAD. Studies examining gender differences in microvascular endothelial function with PAT may need to correct for BAD as a potential confounder.