This study examined whether the autonomic response to passive upright tilt as evidenced by changes in measures of heart rate and blood pressure variability differs between individuals with DS and without DS. Beat-to-beat blood pressure was measured in 26 individuals with Down syndrome (DS) and 11 individuals without DS during 5 min of rest and 5 min of upright tilt. Dependent variables included heart rate, blood pressure, frequency component measures of heart rate and blood pressure variability, and baroreflex sensitivity. The normalized high frequency (HF) power, normalized low frequency (LF) power, and LF/HF of heart rate variability, as well as the LF of blood pressure variability were reduced in persons with DS in response to upright tilt (p<0.05). This was accompanied by smaller change in baroreflex sensitivity (p<0.05) in individuals with DS. Blood pressure responses to upright tilt were also reduced in individuals with DS (p<0.05), but the heart rate response did not differ between groups. Individuals with DS show less vagal withdrawal and sympatho-excitation in response to passive upright tilt. These effects may be partially mediated by smaller change in baroreflex sensitivity in individuals with DS. The results support the hypothesis of altered autonomic modulation in people with DS.
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