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Tony Reybrouck, Joseph Vinckx and Marc Gewillig

This study analyzes whether cardiorespiratory exercise performance is impaired in obese children when parameters of aerobic exercise function are used that are independent of body mass. Twenty-one obese patients (mean age 11.6 ± 2.5 years) were studied and compared with 22 normal controls of the same age range (11.4 ± 2.2 years; p = .78). All participants underwent square wave exercise testing on a treadmill for 6 min (speed 5 km/hr, inclination 4%). The oxygen deficit, calculated as ml·min·kg−1, was expressed as a percentage of the total oxygen cost for the 6-min exercise bout (also expressed as ml·min·kg−1). Oxygen deficit amounted to 7.2 ± 1.9% in the obese patients and was not significantly different (p = .25) from the normal controls (6.6 ± 1.1%). The similar values for O2 deficit in obese patients compared with normal controls shows that cardiovascular fitness in obese patients is normal when parameters of aerobic exercise function are not normalized per kg of body mass.

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Luc Mertens, Tony Reybrouck, Benedicte Eyskens, Wim Daenen and Marc Gewillig

Peak oxygen consumption and anaerobic threshold are both decreased in patients with a Fontan-type circulation. This study wanted to evaluate oxygen uptake kinetics at the onset and at the end of of a steady-state low-level exercise. The delay in cardiorespiratory response was evaluated by calculating the oxygen deficit at the onset of exercise and the recovery half-time at the end. Twelve patients with Fontan circulation (aged 11.4 − SD 5.1 year; 5.2 − 1.9 year after surgery) and 26 normal controls of comparable age (11.3 − 2.2 year) were submitted to a constant-load exercise test of six minutes on a treadmill (speed 5 km/h, inclination 4%). Gas exchange was measured using a breath-by-breath technique. The normalized oxygen deficit was calculated by subtracting the oxygen uptake (VO2) values measured at the onset of exercise from the steady-state VO2 obtained at the end of exercise. These differences were cumulated and expressed as a percentage of the cumulated oxygen cost for the 6 min exercise test. The half-time recovery time was defined as the time to reach 50% of the end exercise VO2 value. The normalized oxygen deficit was significantly higher in Fontan-patients compared to the control group (10.2 − 4.6% vs. 6.1 − 1.3%; p < .001). Also the recovery half-time was significantly higher in the patient group compared to the control group (74.2 − 25.6 s vs. 51.2 − 10.8 s; p < .05). A blunted heart rate response was present in the patients during the first two minutes of exercise, indicating that a slowed cardiac output response could explain the decreased oxygen kinetics in Fontan-patients.

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Ralph K.L. Rogers, Tony Reybrouck, Maria Weymans, Monique Dumoulin, Marc Gewillig and Paul Vaccaro

This study assessed the relationship between the VO2 measured at ventilatory threshold (VT) and the VO2 measured at the point of deflection from linearity of heart rate (HRD). Twelve children (10 boys and 2 girls) with a mean age of 11.3 years (±4.8) performed a graded exercise test to determine VT and HRD. All children had undergone surgical repair for d-transposition of the great arteries at approximately 13 months of age. Because of failure to demonstrate HRD, the data from 4 patients were excluded from statistical analysis. For the remaining 8 patients there was no significant difference between mean VO2 (ml/kg/min) at VT and HRD (26.6 ± 6.4 vs. 26.3 ± 6.8; p > 0.25). Linear regression analysis revealed a correlation of r = 0.92 between the VO2 measured at VT and the VO2 measured at HRD. Only 8 of the 12 patients (66%) in this study satisfied criteria needed to identify the HRD. Therefore HRD may be an accurate predictor of VT in most but not all children who have had surgery for d-transposition of the great arteries.