Chronotropic incompetence in persons with down syndrome

OBJECTIVE: To investigate the chronotropic response to exercise through peak heart rate and the Chronotropic Response Index (CRI) in participants with Down syndrome (DS) and in nondisabled control participants. DESIGN: Comparative study describing the acute exercise heart rate response. SETTING: University sports medicine facility. PARTICIPANTS: Twenty participants with DS (mean age +/- standard deviation, 24.2+/-3.5y) and 20 control participants without disabilities (age, 21.2+/-2.8y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Maximal treadmill exercise tests with metabolic and heart rate measurements. Maximal heart rate and the CRI were considered main outcomes. RESULTS: The peak oxygen consumption (41.7 vs 31.8mL. kg(-1).min(-1)) and peak heart rate (165+/-14.7 vs 192+/-7.7 beats/min) were significantly lower in participants with DS than in controls (P<.05). The CRI was below normal (.84+/-.25) in participants with DS and was normal (.97+/-.07) in controls. CONCLUSION: Both the CRI and the peak heart rates were indicative of chronotropic incompetence in participants with DS, but not in controls. The CRI of the participants with DS was similar to that reported for nondisabled populations who have a true chronotropic response to exercise. The CRI indicated that the low peak heart rate in our participants with DS was a true chronotropic response.