Abstract
Individuals with Down syndrome (DS) have low maximal heart rate (HR) and oxygen uptake (VO2peak). They also have low blood pressure (BP) and a reduced BP and HR response to isometric exercise. Reduced HR, BP and cardiac output (Q) may contribute to the low VO2peak in this population. PURPOSE: To examine the hemodynamic responses to submaximal cycle exercise in individuals with DS compared to non-disabled control (C) group. METHODS: 22 subjects with DS (age=26.2 yrs; wt=73.7 kg; BMI=30.3) and 12 C (age=25.5 yrs; wt=74.4 kg; BMI=26.7) volunteered for the study. Subjects underwent a submaximal cycle ergometry test, 2 minutes of unloaded (UL) activity, followed by 3 min of steady state exercise at 50% of their body weight in Watts. BP was measured using finger plethysmography and cardiac output was calculated using the Model flow algorithm. Subjects also completed a maximal treadmill test with metabolic measurements on a different day. RESULTS: Subjects with DS had lower (p<.05) VO2peak (25.3 vs 39.1 ml/kg/min) and peak HR (168 vs 191 bpm). Comparing subjects with DS to C, HR increased more (p<.05) from rest to UL exercise (76–85 vs 90–91 bpm) but similarly from UL to 37 W (85–101 vs 91–106 bpm). Mean BP (MAP) increased more (p<.05) in subjects with DS from rest to 37 W (77–90 vs 88–94 mmHg). Q was lower (p<.05) in subjects with DS (rest=5.1, UL=7.1, 37W=8.8 l/min) vs C (rest=7.6, UL=8.7 37W= 11.2 l/min). Q was lower as a result of lower stroke volume. These findings were not altered after controlling for peak HR, VO2peak, and body size. CONCLUSIONS: Individuals with DS exhibit normal HR and MAP responses to submaximal cycle exercise. Q increased similarly in both subjects with DS and C, but Q was significantly lower at each stage in subjects with DS. These data suggest that reductions in both maximal HR and Q (as a result of lower stroke volume) contribute to the low VO2peak in individuals with DS.
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