Blood Flow and Blood Pressure Investigation in Down syndrome or Trisomy 21: FBI21

INTRODUCTION: Individuals with Down syndrome (DS) have a reduced work capacity that stems in part from autonomic dysfunction. Autonomic dysfunction may impair the ability to regulate blood flow and blood pressure to working muscles during exercise, which may cause a mismatch between oxygen supply and demand. Our purpose was to comprehensively evaluate blood flow and pressure regulation through two separate research aims: 1) Lower limb dynamic exercise in both relative and absolute intensity workloads on femoral blood flow; 2) Lower limb isometric exercise on the exercise pressor reflex, in individuals with and without DS. METHODS: Twenty-four individuals with DS (M/F: 13/11; 24 ± 5 years; 30.3 ± 6.2 kg/m^2) and without DS (M/F: 13/11; 25 ± 4 years; 26.5 ± 4.5 kg/m^2) completed two visits. Aim 1) participants performed unilateral isotonic knee extensions at 10%, 20%, and 30% of their maximal dynamic power, and at 11 Nm and 16 Nm using their dominant leg on a leg dynamometer. Femoral blood flow was measured using Doppler ultrasound. Aim 2) participants performed 2 minutes of unilateral isometric knee extension at 30% of their maximal voluntary contraction before rapid inflation of a thigh cuff occurred for 3 minutes to isolate the activation of the muscle metaboreflex via post-exercise muscle ischemia (PEMI). Beat-to-beat mean arterial pressure (MAP) was assessed using finger photoplethysmography. RESULTS: Aim 1) Individuals with DS demonstrated blunted femoral blood flow compared to individuals without DS at all relative and absolute intensity workloads (group x time interaction, p<0.001). Aim 2) Individuals with DS demonstrated an attenuated pressor response to unilateral isometric knee extension (MAP; DS: 103 ± 14 vs. Non-DS: 125 ± 19 mmHg), and the reduced MAP response was maintained into PEMI (MAP; DS: 95 ± 13 vs. Non-DS: 106 ± 18 mmHg; group x time interaction, p<0.001). CONCLUSIONS: These data indicate that individuals with DS were unable to adequately direct blood flow to working muscles that could be due to a blunted exercise pressor response that stems from a dampened metaboreflex. These findings contribute to some of the physiological underpinnings of a reduced work capacity observed in individuals with DS.