Blunted heart rate response to upright tilt in people with Down syndrome

Objectives: To determine whether heart rate and blood pressure responses to upright tilt would be lower in subjects with Down syndrome (DS) than in control subjects with no disabilities. Design: Comparative study. Setting: University research laboratory. Participants: Nineteen people with DS (mean age, 25.1±7.3y) and 17 control subjects without disabilities (mean age, 28.4±5.6y). Interventions: Not applicable. Main Outcome Measures: Heart rate and blood pressure recordings were obtained at rest and during a 2-minute period of passive head up tilt to 80°. Results: Heart rate and blood pressure increased significantly during the first 30 seconds of upright tilt in both groups (P<.05) and then stabilized for the remainder of the test. The initial heart rate response to head up tilt (first 30s) was significantly higher in controls compared with subjects with DS (P<.05), whereas the blood pressure response did not differ between groups (P>.05). Controlling for heart rate reserve showed a blunted heart rate response through the tilt period in subjects with DS. Conclusions: These data show a blunted heart rate response to upright tilt in people with DS, despite similar changes in blood pressure, consistent with reduced sympathoexcitation and possibly altered baroreceptor function in these people with DS.