Evaluation of gender differences in endothelium-independent dilation in healthy adults using peripheral arterial tonometry

Abstract

Peripheral arterial tonometry (PAT) is a non-invasive method used to evaluate vascular function. PAT is often used to measure digital pulsatile volume changes in response to reactive hyperemia, which provides a measure of endothelium-dependent dilation (EDD). Reactive hyperemia does not allow one to quantify endothelium-independent dilation (EID), which is typically measured using sublingual nitroglycerin (NTG) mediated dilation. Though most research examining vascular function and cardiovascular disease has focused on EDD, there is evidence that cardiovascular risk factors may impair EID. To our knowledge, PAT has not been used with NTG to determine EID. The purpose of this study was to examine the microvascular vasodilation response to nitroglycerin (NTG) in healthy adults using PAT. Microvascular responses to reactive hyperemia and NTG were evaluated in 86 (41 F, 45 M) healthy subjects (age 37±5 yrs). Beat-to-beat plethysmographic measurements of finger arterial pulse waves were recorded for 5-min following reactive hyperemia. After a 10-min rest period, sublingual NTG (0.4 mg) was administered and PAT signal changes were measured for 10-min. Peak reactive hyperemic index (RHI) and peak NTG-mediated index (NMI) were determined in all subjects. Though there were no significant gender differences in peak RHI (2.07±0.56 F vs. 1.91±0.58 M, P=0.20), peak NMI was significantly greater in females (3.11±1.59 F vs. 2.50±1.34 M, P=0.05). Time to peak NMI was not significantly different between genders (7-min, 28-s [±1-min, 47-s] M, vs. 7-min, 14-s [±1-min, 49-s] F, P=0.58). In this population of healthy adults, RHI did not differ by gender. However, we observed a significantly greater microvascular vasodilation response to NTG using PAT in females than in males. Significance of this finding is unclear, but may indicate the beginning of cardiovascular changes in adult males, as detected with lower peak NMI at the microvascular level. Future studies are needed to determine the exact mechanism underlying the reported gender differences in EID.