Individuals with Down Syndrome (DS) exhibit autonomic dysfunction with reduced sympathetic activity, which may cause reduced aerobic capacity and alterations in peripheral blood flow. Carotid vascular function has been considered as a marker of future cardiovascular events. However, changes in carotid blood flow and vascular conductance in response to sympathoexcitation are not well characterized in persons with DS, carotid stiffness responses to exercise differ between individuals with DS and controls.PurposeTo examine the differences in hemodynamics, carotid vascular reactivity and blood flow following sympathoexcitation using lower body negative pressure (LBNP) in individuals with and without DS.Methods13 young (18 < age <40 yrs) individuals with and without DS (DS=6) participated in this study. Changes in hemodynamics and carotid vascular reactivity (BP, carotid diameter, carotid flow and vascular conductance) were measured before, during and after LBNP (−20 mmHg).ResultsBaseline hemodynamics where not different between the group with DS and controls. The group with DS showed an altered response in conductance to LBNP, when compared to controls with large effect size (η2 = 0.138). In addition, carotid blood flow exhibited a large effect size (η2 = 0.242) for a group interaction. During recovery, the group with DS showed an increase in BF, whereas control group exhibited decrease in BF. These changes occurred without differential changes in carotid diameter and blood pressure.ConclusionsOur results demonstrate the tendency of reduced vascular reactivity in individuals with DS to sympathoexcitation, demonstrated by large effects sizes. Our findings indicate altered blood flow control in persons with DS, attributable to autonomic dysfunction. Larger sample sizes will be needed to confirm these findings. DS (N = 6) Control (N = 7) Baseline LBNP (−20mmHg) Recovery Baseline LBNP (−20mmHg) Recovery Carotid SBP (mmHg) 118 ± 5 111 ± 4 119 ± 5 126 ± 5 114 ± 4 121 ± 4 Carotid DBP (mmHg) 69 ± 4 68 ± 3 68 ± 3 76 ± 3 73 ± 2 77 ± 3 Carotid MAP (mmHg) 87 ± 5 84 ± 3 88 ± 4 96 ± 4 90 ± 3 95 ± 4 Carotid Blood Flow (ml/min) 378.0 ± 110.3 394.1 ± 115.3 399.9 ± 112.2 539 4 ± 102.1 552.6 ± 106.8 500.1 ± 103.9 Carotid Vascular Conductance (ml/min/100mmHg) 25.3 ± 3.6 29.0 ± 4.6 28.1 ± 4.0 32.0 ± 3.3 35.1 ± 3.8 30.7 ± 3.6 Mean ± SEM