Baroreflex sensitivity during static exercise in individuals with Down syndrome

Introduction: Individuals with Down syndrome (DS) have altered heart rate (HR) and blood pressure (BP) responses to orthostatic challenges and isometric handgrip (IHG) exercise, suggesting possible alteration in baroreflex sensitivity. Purpose: This study investigated baroreflex sensitivity (BRS) as a potential mechanism contributing to chronotropic incompetence during IHG in persons with DS. Methods: Heart rate and BP were continually recorded in 12 individuals with DS and 10 controls, at rest and during 2 min of IHG, at 30% of maximal voluntary contraction (MVC). Spontaneous BRS was derived via the sequence method. Results: No differences were seen in HR at rest between groups. Systolic BP (SBP) was significantly lower in the DS group at rest (106.1 +/- 2.9 vs 116.5 +/- 3.9 min Hg, P < 0.05) and during IHG (123.9 +/- 4.6 vs 150.1 +/- 5.3 mm Hg, P < 0.001). A significant group-by-task interaction was found for both change in HR and change in SBP with IHG, because of an attenuated HR and SBP response to IHG in participants with DS (P < 0.05). When controlling for resting,SBP, the DS group had a lower BRS at rest (16.0 +/- 1.7 vs 21.2 +/- 4.2 ms(.)mm Hg-1, P < 0.05) and during IHG (7.8 +/- 1.0 vs 12.1 +/- 2.6 ms(.)mm Hg,(-1) P < 0.05). Conclusions: Individuals with DS have lower BRS at rest and during IHG than controls and this may be related to their attenuated HR response during perturbation.