Attenuated Rapid Onset Vasodilation in Individuals with Down Syndrome

INTRODUCTION: Low work capacity is associated with autonomic dysfunction in individuals with Down syndrome (DS). Autonomic control is essential for appropriate peripheral blood flow delivery and blood pressure (BP) regulation during lower limb dynamic exercise, particularly at the onset of muscular contraction. However, this has not been examined in individuals with DS. Our purpose was to examine the effects of singular lower limb contractions on rapid onset vasodilation and BP in individuals with and without DS. METHODS: Twenty-two individuals with DS (M/F: 11/11; 24±6yrs; 29.0±8.1kg/m 2 ) and n= 24 individuals without DS (CON; M/F: 13/11; 25±4yrs; 26.5±4.5kg/m 2 ) performed single leg extensions at 20%, 40%, and 60% of their maximal dynamic power (MDP) using their dominant leg. Rapid onset vasodilation (ROV) was assessed using femoral blood flow (FeBF) via Doppler ultrasound in the 10 heart beats prior to and 20 heart beats following single leg extensions. Beat-to-beat mean arterial pressure (MAP) and heart rate (HR) were assessed using finger photoplethysmography and a three-lead electrocardiogram, respectively. Femoral vascular conductance (FeVC) was calculated: FeBF/MAP. Area under the curve (AUC) was calculated as the integral of the 20 beats following leg extension using a data acquisition software for both FeBF and FeVC. RESULTS: Individuals with DS demonstrated blunted FeBF (~53% lower), FeVC (50% lower), and AUC (~49% lower) for both FeBF and FeVC, compared to CON at all three relative MDP bouts ( p <0.001). Peak MAP was lower in those with DS at 20% MDP (CON: 97±13 vs. DS: 88±11 mmHg; p= 0.02) and 40% MDP (CON: 99±15 vs. DS: 87±10 mmHg; p= 0.02) bouts, but not 60% of MDP (CON: 97±13 vs. DS: 88±11 mmHg; p= 0.02). Time to peak was not different between groups for any condition (FeBF and FeVC). CONCLUSIONS: Individuals with DS exhibit significantly reduced ROV and BP response to single leg muscle contractions, likely contributing to reduced muscle perfusion. Inadequate ability to perfuse the working muscle impedes the ability to meet the demand of the working muscles and thus, may contribute to the reduced work capacity in this population. Funded in part by the American College of Sports Medicine Foundation Doctoral Student Research Grant (#21-01558). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.