Hemodynamic Responses to Submaximal Cycle Ergometry in Individuals with Down Syndrome

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.