Exercise Performance in Tetralogy of Fallot: The Impact of Primary Complete Repair in Infancy

Primary complete repair (PCR) of tetralogy of Fallot (TOF) is now routinely performed in infancy. Although operative results are excellent, the impact on exercise performance is incompletely understood. We reviewed data of all children with TOF who underwent PCR at our institution and had subsequent maximal cycle ergometer exercise testing between January 1995 and December 2000. Of the 193 patients with TOF who underwent PCR, 57 (30%) underwent exercise testing; maximal tests were available for 50 of 57 (88%). Exercise performance of subjects who underwent PCR at <1 year of age was compared to that of those who underwent repair at >l year of age. The median age at PCR was 10.9 months; 28 subjects (56%) underwent PCR in infancy (<1 year). A transannular incision was employed in the repair in 41 subjects (82%). The mean age at exercise testing was 12.5 +/- 3.2 years. The mean maximal VO2 was 94.9 +/- 18.8% predicted and the mean maximal work rate was 98.0 +/- 20.8% predicted. In multivariate analysis PCR in infancy (age <1 year) was not associated with maximal VO2, peak work rate, peak heart rate, or arrhythmias. Only older age at testing and male gender were significantly associated with higher maximal VO2 (p = 0.005 and p = 0.002, respectively). Intermediate-term exercise performance in subjects who undergo PCR of TOF in early childhood is near normal. Performing PCR in the first year of life does not impact subsequent exercise performance.     

Noninvasive Cardiac Output Measurement at Rest and During Exercise in Pediatric Patients After Interventional or Surgical Atrial Septal Defect Closure

In the majority of patients, secundum atrial septal defects (ASDs) are treated interventionally or surgically, before the onset of clinical symptoms, between 3 and 6?years of age. Because right-ventricular dimensions usually normalize after ASD closure, it has been assumed that cardiac function and exercise performance also normalize at long-term follow-up. The aim of our study was to determine cardiac index (CI) at rest and during exercise at medium-term follow-up of children who had undergone surgical or interventional closure of ASD because no such reports have been published thus far. Seventeen patients (age range 8.8-17.3?years) who underwent surgical correction were included together with 17 subjects who received an interventional procedure with Amplatzer and Helex occluders (age range 12.2-17.3?years). The study was performed after a median interval of 8.6?years (range 6.5-11.6) after the procedure. Twelve healthy children of comparable age served as controls. CI measurements were performed based on the inert gas-rebreathing method with the Innocor system. For exercise testing, the standard treadmill protocol of the German Society of Pediatric Cardiology was used. CI, stroke volume (SV), and heart rate (HR) were determined at rest and at two standardized submaximal exercise levels (levels 3 and 6). CI increased in all subjects under exercise conditions. Neither SV nor HR displayed significant differences between the three groups either at rest or under exercise conditions. Although HR increased continuously, no increase of indexed SV occurred beyond level 3. Noninvasive determination of CI at rest and during exercise with the IGR method is feasible in the pediatric age group. At medium-term follow-up, we found no significant differences between patients who underwent surgical or interventional ASD closure compared with normal controls.     

Cardiopulmonary exercise performance in prematurely born children

Prematurely born children have reduced peak VO2 compared with their peers, inferentially attributed to ventilatory limitation. The primary purpose of this study was to compare exercise ventilation and cardiac output in a sample of childhood survivors of lung disease of prematurity with those of a control group to elucidate reasons for lower peak VO2. A secondary aim was to describe and compare the ventilatory response to incremental exercise. Thirty-two children, aged 8-9 y, were recalled for lung function and progressive exercise tests. Fifteen of them also performed submaximal exercise with measurement of cardiac output (indirect [CO2] Fick) and physiologic dead space. Results were compared with those of term-born, age- and sex-matched, control children. Pulmonary function tests showed mild airflow limitation. Peak VO2 was lower in prematurely born children compared with control children, and was correlated with lean body mass. Their heart rate-VO2 relationship and stroke volume were similar to that of term-born control children. Children with a history of bronchopulmonary dysplasia and hyaline membrane disease as infants exhibited greater exercise hyperpnea than did healthy control children, because of higher breathing frequency, and maintained lower end-tidal PCO2 during submaximal exercise. Physiologic dead space normalized for body weight was similar in preterm and term-born children. Lower peak VO2 in this population is not caused by cardiopulmonary factors, but is best predicted by lean body mass. Ventilation did not limit exercise performance, although it appears that breathing during exercise is regulated differently in prematurely born children than in term-born children.     

Afterload reduction therapy in patients following intraatrial baffle operation for transposition of the great arteries

Patients with intraatrial baffle procedure for transposition of the great arteries (TGA) have diastolic dysfunction, decreased exercise capacity, stroke volume response and elevated systemic vascular resistance (SVR) during exercise. Angiotensin-converting enzyme (ACE) inhibitors improve exercise capacity in adults with congestive heart failure by improving diastolic function and decreasing SVR. We tested the hypothesis that ACE inhibitors decrease SVR and improve exercise capacity in patients after intraatrial baffle procedure for TGA. We studied the effects of enalapril in nine patients with TGA s/p intraatrial switch (mean age, 13.8 ± 3 years) 7 to 21 years (mean, 12 ± 4 years) after intraatrial baffle procedure. Enalapril (0.5 mg/kg/day, maximum dosage 20 mg bid) was administered for 12 months. Patients exercised using a cycle ergometer ramp protocol (0.25 W/kg/min) before enalapril (baseline), 1 month, 6 months, and 12 months after treatment initiation. Heart rate, blood pressure, cardiac output, respiratory rate, minute ventilation, oxygen consumption (VO2), total exercise time, work, and power were measured. SVR, cardiac index, and stroke volume index (SVI) were calculated. Two-tailed paired Student's t-test was used to compare data to those of normal control patients and the patients' baseline data. Patients had lower resting heart rate, cardiac index, maximum heart rate, cardiac index (CI), SVI, VO2, exercise time, work, and power and higher maximal SVR at baseline compared to normal control patients. There was no significant difference in total exercise time, work, power, VO2 (rest/peak), SVR, SVI, and CI after 12 months of therapy compared to patients' baseline values. We conclude that short-term (<1 year) use of enalapril does not improve exercise performance in patients with TGA in whom the intraatrial baffle procedure has been performed.     

Pulmonary function and oxygen uptake during exercise in 11-year-old patients with cystic fibrosis

Ten patients with cystic fibrosis (CF), 5 girls and 5 boys, 11 years of age, underwent pulmonary function and bicycle exercise testing. The material includes all but 2 CF patients in this age group in southern and eastern Norway. The CF children had a moderately reduced pulmonary function, the girls more pronounced than the boys. The mean maximal oxygen uptake (max VO2) in the CF boys was 55 ml/kg/min (94% of age predicted value; range 79-105%), and the CF girls 42 ml/kg/min (79% of age predicted value; range 67-89%). The mean maximal peak heart rate was 195 beats/min. Only one CF girl showed apparent pulmonary limitation during exercise. Increased ventilatory equivalent for oxygen was found during both rest and exercise for the CF girls, but only during rest for the CF boys. Max VO2 was fairly well related to the habitudinal physical activity of the children (r = 0.79).     

Coupling of ventilation and CO2 production during exercise in children

The purpose of this study was to determine how ventilation (VE) and CO2 production (VCO2) in response to exercise change during the growth process in children and teenagers. Dynamic gas exchange responses were measured in two types of studies: 128 healthy children ranging in age from 6 to 18 yr performed progressive exercise tests ("ramp" type protocol) for measurement of the slope of the relationship between VE and VCO2--delta VE/delta VCO2; and the response characteristics of VE and VCO2 in the transition between rest and exercise were measured in 11 teenagers and 11 younger children. Gas exchange was measured breath by breath. We found a small but significant decrease in delta VE/delta VCO2 with increasing body weight (r = -0.46, p less than 0.05), height, or age (mean slope of 27 in the youngest in 21 in the oldest subjects). The response characteristics of VE and VCO2 (measured as the time constant of the best-fit exponential response) were longer than for VO2 in both younger children and teenagers; but the time constants for VE and VCO2 were each approximately 30% faster in younger children compared to teenagers. In addition, end-tidal PCO2 during exercise was significantly lower in the younger subjects (mean value of 39.6 torr) compared to the teenagers (mean value of 43.5 torr). The results suggest that the process of respiratory control in exercise matures to a small degree during childhood in that PCO2 may be regulated at lower levels in younger children and there may be growth-related differences in the relative amounts of CO2 that can be stored in tissues.     

Cardiovascular responses to submaximal treadmill running in 11 to 13 year olds

The influence of age, sex, maturity, body size and body fatness on cardiac output (Q) and stroke volume (SV) during treadmill running at 2.22 m x s(-1) was examined longitudinally. Mass, stature, triceps and subscapular skinfold thickness, and oxygen uptake (VO2) were recorded and Q was estimated using the CO2 rebreathing technique on each of three annual measurement occasions. Maturity was assessed using the indices for pubic hair described by Tanner. At the onset, subjects were 11.3 (0.4) y of age and data were available from a total of 274 Q determinations with equal numbers from boys and girls. Age-, sex- and maturity-associated changes in Q and SV adjusted for differences in body size and fatness were examined using multilevel regression modelling within an allometric framework. Changes in Q in both sexes were essentially in direct proportion to body surface area but, even with anthropometric variables controlled for, girls demonstrated a lower SV than boys, which was compensated for by a higher heart rate (HR) at each observation. CONCLUSION: At a given level of submaximal exercise over the age range 11-13 y Q is directly related to body size in both sexes. With body size and fatness controlled for, boys have greater SVs than girls when exercising at the same absolute VO2, Q and treadmill running speed. Age and maturation do not exert independent effects on either Q or SV.     

Cardiorespiratory response to exercise after the Fontan procedure for tricuspid atresia

Noninvasive exercise testing was used to assess gas exchange in 13 patients age 6-25 yr who had undergone Fontan procedures for tricuspid atresia, five of whom had preexisting Glenn shunts. The results were compared to 28 age- and sex-matched controls. Oxygen saturation was measured by ear oximetry at rest and after exercise. Ventilation, oxygen consumption (VO2), carbon dioxide production (VCO2), and heart rate were measured during progressive exercise. The ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2), mixed expired pCO2 (PECO2) end-tidal pCO2 (PETCO2), and dead space to tidal volume ratio (VD/VT) were determined during steady state exercise on a cycle ergometer. Heart rate was higher for VO2 by 15% (p less than 0.02) and ventilation was higher for both VO2 (by 37%, p less than 0.001) and VCO2 (by 27%, p less than 0.002) in the patients than the controls. Mean VE/VO2 was 35.4 +/- 7.8 (SD) compared to 25.8 +/- 3.1 (p less than 0.001) and mean VE/VCO2 was 41.7 +/- 9.0 compared to 31.6 +/- 4.3 (p less than 0.001). Mean PECO2 was 21.4 +/- 4.4 torr with controls at 27.9 +/- 3.8 (p less than 0.001) and mean PETCO2 was 33.0 +/- 5.3 torr compared to 40.0 +/- 3.3 (p less than 0.001). The patients had a mean oxygen saturation of 92 +/- 5% at rest and abnormal saturation after exercise (87 +/- 9, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Why is exercise capacity reduced in subjects with pectus excavatum?

BACKGROUND: Exercise capacity is often limited in subjects with pectus excavatum (PE), but the mechanism is unknown. OBJECTIVES: We attempted to quantify exercise capacity and to investigate whether limitation of venous return to the heart contributes to exercise intolerance in PE. METHODS: A total of 13 patients with PE (mean age, 19 +/- 6 years) and 20 control subjects (mean age, 25 +/- 11 years) underwent sitting and supine incremental cycling and exercise Doppler stroke volume (SV) measurements. RESULTS: Supine peak oxygen uptake (V'O(2)max) for the patients (1351 +/- 345 mL/min) and control subjects (1505 +/- 330 mL/min) was not different. In contrast, sitting V'O(2)max was lower in the patients than in the control subjects, 1480 +/- 462 and 1994 +/- 581 mL/min, respectively (P =.02). Supine exercise SV was not different between groups. Moreover, only in the patients with PE was supine exercise SV, 70 +/- 18 mL, higher than sitting exercise SV, 55 +/- 14 mL (P =.015). The corresponding values for the control subjects were 70 +/- 18 mL and 65 +/- 19 mL (P = NS). CONCLUSIONS: Patients with PE exercising in the sitting position have reduced V'O(2)max and SV, whereas during supine exercise they approached the control values. The supine advantage in PE suggests that upright exercise capacity in this disease is affected by reduced filling of the heart in the non-supine position.     

Effect of two aerobic training regimens on the cardiorespiratory response of prepubertal boys and girls

The aim of this study was to examine the effect of two endurance training regimens of varying duration and frequency on maximal oxygen uptake (VO2max) of prepubertal boys and girls. The subjects consisted of 84 prepubertal children, aged 10-11 y. Two groups, EG1 (n = 36) and EG2 (n = 20), were involved in a 13 wk endurance training programme (intensity: higher than 80% of maximal heart rate for both groups; frequency: 3 and 2 sessions per week: duration: 25-35 min and 15-20 min per session in the target zone, for EG1 and EG2, respectively). Another group of 28 children served as a control group. Each subject performed a continuous and progressive exercise test to exhaustion on a cycle ergometer to evaluate VO2max before and after the 13 wk study period. The main findings of this study were: (i) there was no improvement in VO2max after a training programme with the following characteristics: 2 sessions per week with 15-20 min of exercise performed at an intensity higher than 80% of maximal heart rate; (ii) a VO2max enhancement (on average +7%) was seen only in children who participated in a training programme organized on the basis of three sessions per week during which exercise intensities higher than 80% of maximal heart rate were sustained for at least 25 min per session; and (iii) there was no gender difference in the training response. Conclusion: It appeared from this longitudinal study that only a programme with continuous activity, organized on the basis of three sessions per week, with 25-35 min at an intensity higher than 80% of maximal heart rate at each session, enhanced VO2max in prepubertal boys and girls.     

Pulmonary Function and Oxygen Uptake during Exercise in 11-Year-Old Patients with Cystic Fibrosis

ABSTRACT. Ten patients with cystic fibrosis (CF), 5 girls and 5 boys, 11 years of age, underwent pulmonary function and bicycle exercise testing. The material includes all but 2 CF patients in this age group in southern and eastern Norway. The CF children had a moderately reduced pulmonary function, the girls more pronounced than the boys. The mean maximal oxygen uptake (max VO₂) in the CF boys was 55 ml/kg/min (94% of age predicted value; range 79-105%), and the CF girls 42 ml/kg/min (79% of age predicted value; range 67-89%). The mean maximal peak heart rate was 195 beats/min. Only one CF girl showed apparent pulmonary limitation during exercise. Increased ventilatory equivalent for oxygen was found during both rest and exercise for the CF girls, but only during rest for the CF boys. Max VO₂ was fairly well related to the habitudinal physical activity of the children ( r =0.79).     

Does carbon dioxide retention during exercise predict a more rapid decline in FEV1 in cystic fibrosis?

BACKGROUND: Carbon dioxide (CO2) retention during exercise is uncommon in mild to moderate lung disease in cystic fibrosis (CF). The ability to deal with increased CO2 is dependent on the degree of airflow limitation and inherent CO2 sensitivity. CO2 retention (CO2R) can be defined as a rise in P(ET)CO2 tension of > or =5 mm Hg with exercise together with a failure to reduce P(ET)CO2 tension after peak work by at least 3 mm Hg by the termination of exercise. AIM: To ascertain if carbon dioxide retention during exercise is associated with more rapid decline in lung function. METHODS: Annual spirometric and exercise data from 58 children aged 11-15 years, with moderate CF lung disease between 1996 and 2002 were analysed. RESULTS: The mean FEV1 at baseline for the two groups was similar; the CO2R group (n = 15) was 62% and the non-CO2 retention group (CO2NR) was 64% (n = 43). The decline in FEV1 after 12 months was -3.2% (SD 1.1) in the CO2R group and -2.3% (SD 0.9) in the CO2NR group. The decline after 24 months was -6.3% (SD 1.3) and -1.8% (SD 1.1) respectively. After 36 months, the decline in FEV1 was -5.3% (SD 1.2) and -2.6% (SD 1.1) respectively. The overall decline in lung function was 14.8% (SD 2.1) in the CO2R group and 6.7% (SD 1.8) in the CO2NR group. Using the primary outcome measure as a decline in FEV(1) of >9%, final multivariate analysis showed that the relative risks for this model were (95% CIs in parentheses): DeltaP(ET)CO2 11.61 (3.41 to 24.12), peak VO2 1.23 (1.10 to 1.43), and initial FEV(1) 1.14 (1.02 to 1.28). CONCLUSION: Results show that the inability to defend carbon dioxide during exercise is associated with a more rapid decline in lung function.     

Effect of training on peak oxygen uptake and blood lipids in 13 to 14-year-old girls

The aim of this study was to investigate the effects of exercise training on the peak oxygen uptake (peak VO2) and blood lipid profile of 13 to 14-y-old postmenarcheal girls. Treadmill determined peak VO2, total cholesterol, high density lipoprotein cholesterol, low density cholesterol, and triglycerides were the outcome measures assessed at baseline and following exercise training. Twenty girls completed a 20-wk programme of exercise training which involved maintaining the heart rate at 75-85% maximum for 20 min, three times per week. Heart rate was rigorously monitored using telemetry throughout each training session. Eighteen girls acted as the control group. There were no significant (p > 0.05) changes in the outcome measures following the training programme. Conclusions: These findings suggest that exercise training of this frequency, intensity and duration for a period of 20 wk has no significant effect on either the peak VO2 or blood lipid and lipoprotein profile of normolipidaemic, postmenarcheal girls.     

Rationale and Design of an International Multicenter Registry of Patients With Repaired Tetralogy of Fallot to Define Risk Factors for Late Adverse Outcomes: The INDICATOR Cohort

Although early survival after tetralogy of Fallot (TOF) repair in the modern era is excellent, studies on late outcomes have shown increasing rates of mortality and morbidity. Despite multiple publications on factors associated with late complications, risk factors for major outcomes (death and sustained ventricular tachycardia [VT]) remain poorly defined. Consequently, the International Multicenter TOF Registry (INDICATOR) was established. This article describes the development, structure, and goals of this registry and characterizes the initial cohort derived from four large congenital heart centers in the United States, Canada, and Europe. A data coordinating center with a core cardiac magnetic resonance (CMR) laboratory and statistical core was established. Subjects with repaired TOF who had CMR imaging performed between 1997 and 2010 and ≥1 year follow-up were included. Clinical end points were death and sustained VT. Demographic, electrophysiologic, exercise, and outcome data were collected. A total of 873 subjects fulfilled inclusion criteria (median age at repair 2.9 years and at CMR imaging 22.8 years). Of these, 9 % had QRS duration >180 ms on electrocardiogram (ECG). On CMR imaging, 38 % had severe right-ventricular (RV) dilatation (≥160 mL/m²), and 6 % had severe RV dysfunction (ejection fraction < 35 %). Of the 551 subjects with exercise testing available, 28 % had severely decreased exercise capacity with <50 % predicted peak oxygen consumption. The INDICATOR cohort allows robust statistical analysis to evaluate major clinical outcomes in patients with repaired TOF. Continued follow-up and further expansion of the registry may provide new insights into innovative therapeutic strategies to improve late outcomes.     

Noninvasive Cardiac Output Determination for Children by the Inert Gas-Rebreathing Method

Standard methods for determination of cardiac output (CO) are either invasive or technically demanding. Measurement of CO by the inert gas–rebreathing (IGR) method, applied successfully in adults, uses a low-concentration mixture of an inert and a blood-soluble gas, respectively. This study tested the feasibility of this method for determining CO during exercise for pediatric patients with complete congenital atrioventricular block (CCAVB) stimulated with a VVI pacemaker. In this study, 5 CCAVB patients (age 9.2–17.4 years) were compared with 10 healthy age-matched boys and girls. Testing was performed with the Innocor system. The patients were instructed to breathe the test gas from a closed system. Pulmonary blood flow was calculated according to the washout of the soluble gas component. During standardized treadmill testing, CO was determined at three defined levels. The CO measurements were successful for all the study participants. The patients reached a lower peak CO than the control subjects (5.9 l/min/m² vs 7.3 [boys] and 7.2 [girls]). The stroke volume increase under exercise also was reduced in the patients compared with the control subjects. The feasibility of the IGR method for exercise CO testing in children was documented. Application of the IGR method for children requires careful instruction of the patients and appears restricted to subjects older than 8 years. The method offers new insights into mechanisms of cardiovascular adaptation in children with congenital heart disease.     

Predictors of VO2Peak in children age 6- to 7-years-old

This study investigated the predictors of aerobic fitness (VO2PEAK) in young children on a population-base. Participants were 436 children (229 boys and 207 girls) aged 6.7 ± 0.4 yrs. VO2PEAK was measured during a maximal treadmill exercise test. Physical activity was assessed by accelerometers. Total body fat and total fat free mass were estimated from skinfold measurements. Regression analyses indicated that significant predictors for VO2PEAK per kilogram body mass were total body fat, maximal heart rate, sex, and age. Physical activity explained an additional 4-7%. Further analyses showed the main contributing factors for absolute values of VO2PEAK were fat free mass, maximal heart rate, sex, and age. Physical activity explained an additional 3-6%.     

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??Objective??To evaluate the chronotropic competence in children with vasovagal syncope ??VVS??. Methods??Thirty-nine patients??17 males??22 females??age ranging from 8-16 years?? with syncope were included in the study??and 28 were diagnosed with VVS??including 15 cases of vasodepressor type??9 cases of mixed type??and 4 cases of cardioinhibitory type??11 were with unexplained cause of syncope. A treadmill test was performed and heart-rate response during exercise was evaluated by the chronotropic reserve. Demographic data and change of heart rate??blood pressure during test and CRI were compared between the 2 groups and different types of VVS. Furthermore??based on CRI??patients with VVS were divided into the normal chrontropic group??n??10?? and CI group??n??17??. By following the recurrence of syncope of 2 groups??the effect of CI on the prognosis of VVS in children was observed. Results??There were no significant differences between children with VVS and with unexplained syncope in sex??age??BMI??baseline heart rate??MaxMET or baseline blood pressure. But during exercise test??peak heart rate and CRI were significantly lower in children with VVS than in unexplained syncope. The incidence of CI in children with VVS was significantly higher than that in children with unexplained syncope??64.3% vs. 27.3%??P??0.05??. The incidence of CI in VVS with vasodepressor-type in children was significantly lower than those with cardioinhibitory-type and mixed-type. During following-up period??the recurrence rate of syncope in VVS children with CI was significantly higher than that of children without CI. Patients with CI had significantly worse prognosis compared to those without CI??Log-rank??P??0.028??. Conclusion??Chrontropic competence is significantly altered in children with VVS??especially in cardioinhibitory-type and mixed-type in children. CI is the significant predictor for poor prognosis in children with VVS.     

Exercise Performance in Patients with D-Loop Transposition of the Great Arteries After Arterial Switch Operation: Long-Term Outcomes and Longitudinal Assessment

The first patients to undergo a successful arterial switch operation (ASO) for d-transposition of the great arteries (D-TGA) are now entering their fourth decade of life. Past studies of ASO survivors’ exercise function have yielded conflicting results. We therefore undertook this study to describe the current function of ASO survivors, to identify factors related to inferior exercise performance and to determine whether their exercise function tends to deteriorate over time. A retrospective cohort study was designed examining all patients with D-TGA after the ASO who underwent comprehensive cardiopulmonary exercise testing (CPET). Patients with palliative surgery prior to ASO, ventricular hypoplasia or severe valvar dysfunction were excluded from the study. Data from CPETs in which the peak respiratory exchange ratio was <1.09 were also excluded. We identified 113 patients who met entry criteria and had 186 CPX at our institution between 1/2002 and 1/2013; 41 patients had at least 2 qualifying CPX. Mean age at the time of the initial test was 17 ± 1 year. Peak oxygen consumption (VO2) averaged 84 ± 2 % predicted. Peak VO2 was lower among patients with repaired ventricular septal defects (82 ± 4 vs. 86 ± 3 % predicted; p < 0.05) and among patients with ≥ moderate right-sided obstructive lesions (77 ± 5 vs. 87 ± 3 % predicted; p < 0.05). Surgery prior to 1991 was also associated with a lower peak VO2 (81 ± 3 vs. 87 ± 3 % predicted; p < 0.01). The mean % predicted peak heart rate was 92 ± 1 %, with no significant difference between any of the subgroups. Non-diagnostic exercise-induced STT changes developed in 10 patients (12 studies). In the subgroup with at least 2 exercise tests, the annual decline in % predicted peak VO2 was quite slow (?0.3 % points/year; p < 0.01 vs. expected normal age-related decline). The exercise capacity of ASO survivors is well preserved and is only mildly reduced compared to normal subjects. Moreover, there is only a slight deterioration in exercise capacity over time. VSD repair, residual right-sided obstructive lesions, and earlier surgical era are associated with worse exercise performance. Peak heart rate was preserved with no significant change in follow up testing.     

Effect of hypoxia on ventilatory control during exercise in children and adults

Little is known about maturation of peripheral chemoreceptor tone (PCT) during growth. We recently demonstrated that the increase in PCT was 49% greater during hypoxic (15% O2) exercise in children compared to adults. As the PCT is a major determinant of ventilatory (VE) response at the onset of exercise (measured by the time constant tau), we hypothesized that hypoxia would affect tau VE (and tau VCO2) to a greater extent in children. Nine healthy children (6-10 y old) and nine healthy adults (18-40 y old) performed multiple transitions from rest to constant work rate on the cycle ergometer. Studies were done breathing 21% O2 and 15% O2. Hypoxic breathing quickened the VE responses in all of the adults and children, but the magnitude of the hypoxic effect did not differ between the two groups (in children, tau VE was 50.9 +/- 9.9 s during 21% O2 breathing and 32.6 +/- 6.9 s during hypoxia; in adults, tau VE was 69.4 +/- 17.6 s, which fell to 50.9 +/- 18.4 s during hypoxia). The hypothesized greater ventilatory response to hypoxia in children compared to adults during exercise was not observed. During 21% O2 breathing, the data demonstrated that children stored relatively less CO2 (by 49%) than did adults in the transition between rest and exercise, possibly explaining the faster ventilatory kinetics. We speculate that there must be additional respiratory control differences between adults and children such that for a given increase in PCT-induced by hypoxia, the VE response at the onset of exercise is less in children than in adults.     

Exercise protocols to estimate Fatmax and maximal fat oxidation in children

Consensus on the exercise protocol used to measure Fatmax (exercise intensity corresponding to maximum fat oxidation (MFO)) in children has not been reached. The present study compared Fatmax estimated using the 3 min incremental cycling protocol (3-INC) and a protocol consisting of several 10 min constant work rate exercise bouts (10-CWR) in 26 prepubertal children. Group Fatmax values were the same for 3-INC and 10-CWR (55% VO2peak) and 95% limits of agreement (LoA) were ± 7% VO2peak. Group MFO values were similar between protocols, although 95% LoA were -94 to 113 mg·min-1. While 3-INC provides a valid estimation of Fatmax compared with 10-CWR, caution should be exercised when estimating MFO in prepubertal children.