Normal HR with tilt, yet autonomic dysfunction in persons with Down syndrome

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Down Syndrome Research

Background:

• Individuals with Down syndrome (DS) exhibit distinct autonomic nervous system (ANS) function at rest and during adrenergic stimulation.
• Previous research indicates altered autonomic responses in DS, but a detailed comparison of heart rate variability (HRV) during orthostatic stress is lacking.
• Understanding these autonomic differences is crucial for managing cardiovascular health in persons with DS.

Purpose of the Study:

• To compare cardiac autonomic function between individuals with and without DS during upright tilt using HRV analysis.
• To investigate if HRV responses during tilt differ in persons with DS, particularly when matched for heart rate (HR) changes.
• To elucidate the sympathetic and parasympathetic nervous system balance during orthostatic challenge in DS.

Main Methods:

• A case-control study involving 15 individuals with DS and 15 age- and sex-matched controls.
• Participants underwent a 5-minute passive upright tilt at 80°. A subset of individuals with DS (n=11) were not matched for HR response.
• Heart rate variability (HRV) was analyzed in both time (RMSSD) and frequency domains (LnLF, LnHF, LF/HF ratio, TP) before and during tilt.

Main Results:

• While HR changes were similar in DS-matched and control groups, they were lower in the unmatched DS group.
• Both DS groups showed a reduction in low-frequency power (LnLF), indicating altered sympathetic activity, unlike the control group.
• The increase in the LF/HF ratio, a marker of sympathetic dominance, was attenuated in the unmatched DS group compared to controls.

Conclusions:

• Despite similar heart rate responses to upright tilt in matched groups, individuals with Down syndrome demonstrate reduced sympathetic nervous system dominance.
• These findings highlight persistent alterations in autonomic cardiovascular regulation in persons with DS during orthostatic stress.
• Further research is warranted to explore the clinical implications of these autonomic differences in the DS population.