Cardiopulmonary exercise test (CPET)
The CPET was performed using the Vyntus CPX (Carefusion, Germany) linked
to a gas analysis system (CardiO2 System; Medical
Graphics Corporation, MN, USA). The adolescents performed a
ramp-symptom-limited CPET consisting of 2 minutes (min) of rest, 3 min
of warm-up (unloaded pedaling), and an incremental work period (15 W/min
for height < 150 cm and 20 W/min for height ≥ 150 cm) (7).
During the test, the adolescents were instructed to continue pedaling at
60 rpm. The test was set to last from 8 to 12 minutes until 90% of the
maximal heart rate (HR) predicted was reached, and 1.10 of the
respiratory exchange rate (RER) was considered available (7). Oxygen
saturation (SpO2) was measured via pulse oximetry (Onyx,
model 9500; Nonin, Plymouth, MN), and the electrocardiography signals
(Welch Allyn CardioPerfect, Inc., NY) were monitored continuously during
the tests. The following variables were recorded: power, peak oxygen
uptake (VO2peak), minute ventilation (VE), carbon
dioxide production (VCO2), RER, and HR. Additionally,
blood pressure, the Borg score for leg discomfort, and severity of
dyspnea were measured at rest and every 2 min during the test until the
end of the test (19). Males and females were considered to have aerobic
fitness when they reached VO2peak ≥ 43.4 and ≥ 35.6
ml/kg/min, respectively. If these thresholds were not met, they were
considered to have low aerobic fitness (20). The tests were performed in
accordance with the American Thoracic Society recommendations. The
predicted CPET values were calculated for a Brazilian population (21).