Heart rate variability at rest and during exercise in persons with Down syndrome.
OBJECTIVE
To determine whether autonomic dysfunction explains chronotropic incompetence observed in persons with Down syndrome (DS) and to measure heart rate variability (HRV) at rest and during exercise in persons with mental retardation with and without DS.


METHODS
Comparative study.


METHODS
University exercise science laboratory.


METHODS
Thirty-one subjects with mental retardation (age, 20.2 y) with DS (n=16; 10 men, 6 women) and without DS (n=15; 8 men, 7 women).


METHODS
Not applicable. Main outcome measures HRV was determined at rest and at 2 steady-state exercise intensities on the treadmill in both time (standard deviation of the R-R interval, percentage of R-R intervals deviating by more than 50 ms from the previous R-R interval [deviation >50], square root of the mean squared differences of successive differences) and frequency (low-frequency power [LF]), high-frequency power [HF], the LF/HF ratio) domains.


RESULTS
The DS group demonstrated a statistically lower peak heart rate (161 beats/min vs 178 beats/min, P<.05), and peak oxygen consumption (27.4 mL.kg(-1).min(-1) vs 34.3 mL. kg(-1).min(-1), P<.05) than did the group with mental retardation without DS. At rest, all time domain measures of HRV and absolute HF power were significantly higher in the DS group (P<.05). Yet, LF power and LF/HF values did not differ between groups. All HRV variables decreased significantly at both exercise intensities, with no differences between groups during exercise (P<.05).


CONCLUSIONS
People with DS have greater parasympathetic activity at rest, but group differences disappear with the onset of exercise, which suggests that other variables are responsible for chronotropic incompetence in persons with DS.
Exercise Science Department, Syracuse University, Syracuse, NY 13244-5040, USA. tbaynard@syr.edu
Tracy
T
Baynard
Ken H
KH
Pitetti
Myriam
M
Guerra
Bo
B
Fernhall
D000328:Adult; D000704:Analysis of Variance; D001342:Autonomic Nervous System Diseases / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology*; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D016022:Case-Control Studies; D004314:Down Syndrome / Q000150:complications*; D004562:Electrocardiography; D015444:Exercise; D005080:Exercise Test / Q000379:methods; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D010366:Peak Expiratory Flow Rate; D011237:Predictive Value of Tests; D012146:Rest; D012815:Signal Processing, Computer-Assisted; D012849:Sinoatrial Node / Q000503:physiopathology; D014938:Work Capacity Evaluation