Sex‐Related Differences in Rapid‐Onset Vasodilation with Aging

Abstract

Rapid‐onset vasodilation (ROV) in response to a single muscle contraction is attenuated with aging. Moreover, sex‐related differences in muscle blood flow and vasodilation during dynamic exercise have been observed in young and older adults. The purpose of the present study was to explore if sex‐related differences in ROV exist in young (n=36; 21 male/15 female; 25 ± 1 yr) and older (n=32; 19 male/13 female; 66 ± 1 yr) adults. Subjects performed single forearm contractions at relative intensities of 10%, 20%, and 40% maximal voluntary contraction (MVC). Brachial artery blood velocity and diameter were measured with Doppler ultrasound, and forearm vascular conductance (FVC; ml·min−1·100 mmHg−1) was calculated from blood flow (ml·min−1) and blood pressure (mmHg) and used as a measure of peak ROV (peak change in FVC from baseline). Due to significant differences in MVC and consequent differences in weight used for each relative intensity between males and females, the data were analyzed two additional ways. First, responses were normalized for workload (i.e. peak FVC per kg of weight lifted). Second, the peak ROV responses in a subset of subjects (n=44; 12 young male, 10 young female, 11 older male, 11 older female) with similar absolute workloads (10–12kg) were compared. Lastly, the magnitude of change in peak ROV with increasing intensity (calculated as the slope of a linear regression line between 10, 20, and 40% MVC) was calculated and compared between groups. Peak ROV was attenuated in females across all relative intensities in the young and older groups (P < 0.05). When normalized for workload, peak ROV was attenuated with age in both males and females at all intensities (P<0.05) except at 10% for females (P=0.47). However, sex‐related differences were not observed within age when normalized by workload at any intensity (P>0.05). In the subset of subjects with a similar absolute workload (~11kg), age‐related differences in ROV remained in both the female and male groups (P<0.05). Older females demonstrated an attenuated peak ROV compared to their older male counterparts (91 ± 6 vs. 121 ± 11 ml·min−1·100 mmHg−1, P<0.03), whereas no sex differences in peak ROV were observed between young females and males (134 ± 8 vs. 154 ± 11 ml·min−1·100 mmHg−1, P=0.15). Examining the slope of the peak ROV response across contraction intensities revealed a main effect of age (P<0.05), with the slope being blunted in older compared to young subjects. When separated by sex, the slope was smaller in older compared to young females (5.5 ± 0.7 vs. 8.9 ± 0.9 FVC units/intensity, P<0.05) but not between older and young males (7.0 ± 0.50 vs. 8.2 ± 1.0 FVC units/intensity, P=0.38). Our data suggest that sex‐related differences in the rapid vasodilatory response to single muscle contractions exist in older but not young adults, such that older females have a blunted response compared to older males.