Hemodynamic and Peripheral Vascular Conductance in Individuals with Down Syndrome Following Hypovolemic Pressure Challenge

Abstract

Autonomic dysfunction, which contributes to chronotropic incompetence and reduced peak aerobic capacity (VO2peak), is a common condition in individuals with Down syndrome(DS). Impaired vascular conductance and hemodynamics to sympathoexcitation have been associated with autonomic dysfunction. Lower level of lower body negative pressure (LBNP) has been used to study autonomic function as a controlled stimulus. PURPOSE: To examine the differences in hemodynamics and peripheral vascular reactivity to sympathoexcitation using hypovolemic lower body negative pressure (LBNP) in individuals with and without DS. METHODS: Twenty four volunteers (DS=12, 24 yrs; Control=12, 23 yrs) participated in this study. VO2peak was obtained via indirect calorimetry by an individualized maximal exercise treadmill protocol. Changes in hemodynamics and vascular reactivity (HR, BP, brachial diameter, blood flow and vascular conductance) were measured before, during and after LBNP (-20 mmHg). RESULTS: Compared with controls, individuals with DS have lower VO2peak (25.0 ± 1.7 vs. 42.5 ± 1.7 ml/kg/min for DS and controls, respectively) and higher BMI (23.1± 1.7 vs. 31.9 ± 1.8 kg/m2 for controls and DS, respectively) (p<0.05). There were no group differences in hemodynamics at baseline. There was significant interaction in brachial blood flow (p <0.05) and trend to significant vascular conductance (p = 0.08) with decreased blood flow and vascular conductance in controls, whereas the group with DS did not exhibit changes with hypovolemic challenge. CONCLUSIONS: Our results demonstrate absences of vascular reactivity to sympathoexcitation in individuals with DS. This may indicate that individuals with DS exhibit autonomic dysfunction.