Cardiopulmonary exercise testing in children following surgery for tetralogy of Fallot

The purpose of this study was to compare the cardiopulmonary responses at rest and during exercise of children following surgical correction of tetralogy of Fallot. The physiologic measurements assessed at rest and during maximal treadmill exercise included diffusing capacity of the lung for carbon monoxide, heart rate, oxygen consumption, minute ventilation, and cardiac output. Twenty children with repaired tetralogy of Fallot served as the study group, and 20 normal boys and girls served as controls. Subjects with tetralogy of Fallot had significantly lower values than those of control subjects for maximal cardiac output and somewhat lower values for diffusing capacity of the lung for carbon monoxide and heart rate. We conclude that the exercise cardiac function of children with surgically corrected tetralogy of Fallot is somewhat diminished compared with that of control children. This information is necessary to establish safe, yet effective exercise guidelines for this select population.     

Longitudinal Changes in Heart Rate-Corrected Measures of Exercise Performance in Children

Interpretation of change in exercise performance over time in children with repaired congenital heart disease is often hampered by poor effort that limits the maximum heart rate; this is often difficult to distinguish from chronotropic impairment, a common finding in these children. In an attempt to address this limitation, we sought to examine measures of exercise performance that are corrected for heart rate in healthy children and to determine if these change with somatic growth. We studied two serial graded exercise tests in 24 healthy children at an interval of >3 years. Paired comparisons revealed that maximum oxygen pulse (O₂ pulse), O₂ pulse at ventilatory anaerobic threshold, O₂ pulse at a heart rate of 140 beats per minute, and slope of the VO₂–heart rate relationship all increased with age. However, when indexed to somatic growth, there was no change in the mean values of these parameters over time. We conclude that O₂ pulse and slope of the VO₂–heart rate relationship during exercise increase in proportion to somatic growth in children so that optimal oxygen delivery to the exercising muscles is ensured. This study provides the “normative” response of exercise parameters to growth, against which responses of children with repaired congenital heart disease may be compared.     

Responses of non-obese white children to treadmill exercise

OBJECTIVE: To determine the response to maximal treadmill exercise with the Bruce protocol in a cohort of healthy non-obese American children and adolescents. STUDY DESIGN: A retrospective review of treadmill exercise studies on 347 white American children (188 boys, 159 girls) aged 5 to 18 years was performed with metabolic criteria to verify maximal exercise effort. Data on exercise endurance time, heart rate, blood pressure, and metabolic variables were assessed and compared between age groups and sexes by unpaired t testing and analysis of variance. RESULTS: Exercise endurance time was lower in all age groups when compared with earlier published data. Girls had a lower endurance time than boys at all ages. There was no significant difference in maximum heart rate with respect to age or sex. The maximum systolic blood pressure and diastolic blood pressure increased with increasing age in both boys and girls. Boys had significantly higher maximum systolic blood pressure and diastolic blood pressure after 13 years of age. The maximum absolute oxygen consumption and indexed oxygen consumption showed similar trends for both sexes. CONCLUSION: Lower exercise endurance times are seen despite physiologic evidence of maximal effort, raising the possibility that cardiovascular conditioning is reduced in contemporary American children.     

Hemodynamic Correlates of Clinical Severity in isolated ventricular septal defect

Summary To test the hypothesis that the clinical assessment of severity in ventricular septal defect would be more related to variables which define tissue oxygen delivery than variables which define the left-to-right shunt, cardiac catheterization data from 40 children <3 years of age were assessed. Variables which were considered indicative of clinical severity included the need for digoxin and diuretics, resting heart rate, and severity of growth failure. Variables measured at cardiac catheterization, including those which related to oxygen transport, and assessment of left-to-right shunt, were considered independently. Patients receiving digoxin and diuretics were more tachycardic (142±18 vs. 111±26 beats/min, p<0.001) and had lower superior vena cava oxygen saturation (64±6 vs. 69±5%, p<0.01). Variation in heart rate (r ²=0.46) was best explained by oxygen consumption, hemoglobin concentration, cardiac index, and pulmonary vascular resistance. Variation in growth failure (r ²=0.15) was related only to the left ventricular forward stroke index. These data suggest that variables related to oxygen delivery, including oxygen consumption, hemoglobin concentration, cardiac index, forward stroke index, and superior vena cava oxygen saturation, are the major contributors to the clinical assessment of severity in ventricular septal defect.     

Noninvasive Measurement of Cardiac Output During Exercise in Children with Tetralogy of Fallot

In patients with surgically repaired tetralogy of Fallot (TOF), reported peak oxygen consumption (VO(2)) is decreased compared with control subjects. The measurement of exercise cardiac output (CO) could be a useful adjunct for assessing cardiovascular fitness. There are few data assessing noninvasive CO, cardiac index (CI), and stroke volume (SV) during exercise for these patients. This study sought to measure noninvasive CI and SV during rest and exercise in children with repaired TOF. The authors compared 21 asymptomatic children with repaired TOF ages 11-17?years during rest and exercise and 42 gender- and age-matched healthy control children without structural heart disease. Using a Bruce exercise protocol, exercise data were measured noninvasively by a novel inert gas rebreathing technique including peak duration and heart rate, as well as VO(2), CO, CI, and SV measured at 90?% of peak predicted theoretical heart rate (90 % ppHR). Statistical correlation between peak VO(2) and CI was performed. At baseline, there was no statistically significant difference in any of the measures between the groups. At 90 % ppHR, there was an increase in CI during exercise of 140 % in the TOF children and 180 % in the control children. During exercise, SV changed minimally in the patient group, whereas it increased more than 30 % in the control children. At 90 % ppHR, the patient group showed an increase in VO(2) during exercise similar to that of their healthy peers. The patients had a significantly shorter peak exercise duration than normal control subjects. The patients had a lower CI during exercise because they were less able to increase SV. Therefore, at similar heart rates, patients who have had TOF repair must rely on increased peripheral muscle extraction, with a higher arteriovenous oxygen difference (SaO(2)-MvO(2)) during exercise, which may limit peak exercise capacity. In this cohort of TOF patients, noninvasive CI measurement was feasible, and correlation with VO(2) was good.     

The relationship between autonomic nervous activity and physical activity in children

BACKGROUND: There have been few studies that have reported on heart rate variability and the development of autonomic nervous function in children. This study investigated the relationship between heart rate variabilities at night and physical activity in children. METHODS: The study subjects were 29 children, including 17 boys and 12 girls. The daily activity product and heart rate variabilities during sleep at night (00.00-05.00 hours) were measured and several aspects of these parameters were analyzed. In one child (an 8-year-old girl), heart rate variability and the physical activity product were measured for 12 days. RESULTS: There was a negative correlation between the mean R-R interval and the duration (min) of heavy exercise per day (r = -0.39, P < 0.05). In the 8-year-old girl, from whom data was obtained for 12 days, the duration of heavy exercise per day was negatively correlated with the mean R-R interval (r = -0.63, P < 0.05), the number of changes in successive R-R intervals greater than 50 msec (RR50) (r = -0.74, P < 0.01), and the high frequency (HF) component (r = -0.66, P < 0.05). Furthermore, the daily number of steps was negatively correlated with the mean R-R interval (r = -0.66, P < 0.05), RR50 (r = -0.71, P < 0.05) and the HF component (r = -0.66, P < 0.05). There was a negative correlation between the amounts of energy consumption and the mean R-R interval (r = -0.69, P < 0.05). There was a negative correlation between the amounts of energy consumption and RR50 (r = -0.76, P < 0.01). Moreover, there was also a negative correlation between the amount of energy consumption and the HF component (r = -0.71, P < 0.05). CONCLUSION: These findings suggested that physical activities increase heart rate during sleep, but reduce parasympathetic nervous activity at night. Because both the HF component and RR50 reduce with growth, the exercise-related inhibition of parasympathetic nervous activity may be a developmental stimulus to reach a balanced autonomic nervous pattern in adults.     

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.     

Oxygen Pulse Kinetics in Fontan Patients During Treadmill Ramp Protocol Cardiopulmonary Exercise Testing

After single-ventricle palliation, patients have variable long-term functional outcomes. Cardiopulmonary exercise testing (CPET) is an assessment tool used to quantify functional outcome. Oxygen pulse kinetics during CPET, which can be an important indicator of dynamic changes in stroke volume reserve, has not been systematically studied in this population. This study aimed to analyze oxygen pulse kinetics during a treadmill ramp protocol among patients with Fontan physiology compared with that of normal subjects and to explore the ability of oxygen pulse kinetics to define functional status further. Peak oxygen pulse and change in oxygen pulse during ramp treadmill CPET were retrospectively collected and compared between 44 Fontan patients and 85 age- and sex-matched control subjects. The peak oxygen pulse was significantly lower in the Fontan group (9.80?±?4.11?ml/beat) than in the control group (13.62?±?4.7?ml/beat) (p????0.001). The resting oxygen pulse did not differ between the two groups (3.13?±?1.23 vs. 3.09?±?1.33?ml/beat; p?=?0.88). The oxygen pulse was higher in the patients with chronotropic insufficiency, but the difference was not statistically significant (11.11?±?4.97 vs. 9.25?±?3.63?ml/beat; p?=?0.17). Regression analysis showed a significant difference in the slope of the oxygen pulse-to-workload relationship. The Fontan group showed no relation between degree of reduction in the oxygen pulse from peak to end of exercise and the underlying defect, peak heart rate, peak oxygen consumption, ventilatory anaerobic threshold (VAT), expired volume (VE)/carbon dioxide output (VCO₂) at the VAT, maximum heart rate, or minimum oxygen saturation. Analysis of oxygen pulse kinetics in Fontan patients suggests that there is an early and progressive limitation in stroke volume compared with control subjects. This limitation may be partially masked by increased oxygen extraction. In patients with chronotropic insufficiency, absolute or body surface area-indexed oxygen pulse may be higher than in those with a normal heart rate response. A composite assessment of the oxygen pulse and oxygen pulse kinetics, including the oxygen pulse slope and the percentage of reduction in oxygen pulse from peak to end of exercise, may allow a more comprehensive assessment of the degree of cardiac limitation in this group of patients.     

Anaerobic threshold and the determination of training target heart rates in premenarchal girls

Summary The capability of children to respond to endurance training with increased aerobic capacity is unclear. Prepubertal subjects may require higher target heart rates than adults to increaseV o ₂ max, and previous studies failing to demonstrate aerobic trainability in children may have involved inadequate exercise intensity. In this study, heart rates at the anaerobic threshold, measured noninvasively as the ventilatory breakpoint (VBP), were determined during treadmill testing of 12 premenarchal girls to establish a metabolic-based target rate. The mean heart rate at VBP was 171 beats/min (±12 SD) with a range from 147 to 194 beats/min. Although a wide intersubject variability was observed, the rates at VBP exceeded those predicted by standard formulas for calculating target heart rates in adults by over 10 beats/min in a majority of the girls. These data indicated that target heart rate guidelines designed for training older individuals may not adequately stress oxygen delivery systems in prepubertal subjects.     

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).     

Exercise testing in children with congenital heart disease before and after surgical treatment

Summary Pre- and postoperative exercise tests were performed on 12 children with severe congenital heart disease (CHD) (age, 4–12 years). Oxygen uptake, blood pressure, and heart rate responses to exercise were measured. Exercise test time and the tolerable speed of the treadmill increased significantly after the operation. When pre- and postoperative values were compared, exercise heart rates did not change in most of the children, while delta systolic blood pressure rose significantly. The significant increase in peak oxygen consumption (VO₂/Kg) values also revealed that there was an improvement in their exercise capacity after the operation.     

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).     

Lack of physical activity in young children is related to higher composite risk factor score for cardiovascular disease

Aim: This study evaluates whether accelerometer‐measured physical activity is related to higher composite risk factor scores for cardiovascular disease (CVD) in children. Methods: Cross‐sectional study that included 223 children aged 7.9–11.1 years (boys n = 123, girls n = 100). Daily physical activity was assessed by accelerometers for 4 days. Body fat was quantified by dual X‐ray absorptiometry. Maximal oxygen uptake was measured during a maximal exercise test. Resting heart rate and blood pressure were measured. Z‐scores [(value for the individual ? mean value for group)/SD] were calculated for each variable, and the sum of different risk factor z‐scores used as an index of composite risk factors score for CVD. Results: Partial correlations, from General Linear Model, between moderate to vigorous physical activity (MVPA), vigorous physical activity (VPA) and general physical activity versus index of composite risk factor score were in boys 0.29, 0.33 and 0.30 (all p < 0.05), respectively. The corresponding correlations in girls were ?0.28, ?0.32 (both p < 0.05) and ?0.18 (NS), respectively. Conclusion: Low amounts of MVPA and VPA were related to higher composite risk factor scores for CVD in children aged 8–11 years.     

Kidney transplanted child and sport practices]

OBJECTIVE: Evaluation of physical capacity in kidney transplanted children for sport practice adequacy. POPULATION AND METHODS: A retrospective study was carried out in 32 children transplanted at least one year before evaluation. We studied auxology, respiratory function testing, cardiovascular parameters at rest and after exercise, and aerobic capacity performed during a triangular effort test. RESULTS: Kidney transplanted children were smaller and had a higher body mass index (IMC). Breathing parameters and cardiac ultrasound examinations were normal in all but one child. After exercise, four children had high systolic blood pressure requiring a treatment adaptation. Lower values of maximal aerobic power (Pmax) and oxygen maximal uptake (VO2max) were noticed, mainly in girls. CONCLUSION: Kidney transplanted children have a good physical exercise tolerance. Therefore they can be allowed to practise sports at school or in a club after a normal effort test (taking into account the risk of transplant trauma).     

Evidence of α-Adrenoceptor-Mediated Chronotropic Action in Children

We investigated α-adrenoceptor-mediated positive chronotropic action in children using a pharmacological autonomic function test. Under cardiac vagal and sympathetic blockade, chronotropic responses to intravenous infusion of an α-agonist, phenylephrine, were determined in 129 patients with suspected autonomic dysfunction. Heart rate changes to phenylephrine infusion (0.4 μg/kg/min) for 5 minutes ranged from −2 to 50 beats/min (mean ± SD, 13.8 ± 9.7 beats/min). α-Adrenoceptor-mediated chronotropic (APC) action more than 5 beats/min was observed in 88 (68%) subjects. APC was negatively correlated with age. Multivariate analysis showed that APC was correlated negatively with β-sympathetic tone and positively correlated with intrinsic heart rate. These results suggest that the α-adrenoceptor-mediated chronotropic action is a developmental phenomenon and may play an important role in controlling heart rate in response to cardiac sympathetic activation.     

Dexmedetomidine for Patients Undergoing Diagnostic Cardiac Procedures: A Noninferiority Study

When anesthetizing children with congenital heart disease for diagnostic cardiac catheterization, anesthesiologists and cardiologists seek to use anesthetic regimens that yield minimal hemodynamic changes and allow for spontaneous ventilations. Recently, dexmedetomidine has been used as an anesthesia adjunct because of its sedative and analgesic properties and minimal ventilatory depressive effects. We tested the hypothesis that the combination of sevoflurane and dexmedetomidine is non-inferior to sevoflurane alone as it refers to hemodynamic measurements during diagnostic cardiac catheterization in children with a transplanted heart, one ventricle (Fontan procedure), or normal cardiac physiology. Patients were anesthetized with inhalation of sevoflurane in nitrous oxide/oxygen and, after baseline hemodynamic measurements, successive boluses of dexmedetomidine followed by continuous infusion were administered. In this study, non-inferiority was shown when differences at steady-state (dexmedetomidine + sevoflurane) compared to baseline (sevoflurane alone) and its associated 95% confidence interval fell completely within the range of plus or minus 20%. Forty-one (26 normal physiology, 9 cardiac transplantation, and 6 Fontan) patients were enrolled. Non-inferiority of sevoflurane + dexmedetomidine compared with sevoflurane alone was shown for heart rate, but not for arterial blood pressure in patients with normal and cardiac transplant physiology. In patients with normal cardiac physiology, non-inferiority was demonstrated for bispectral index. Therefore, while the lack of depressive respiratory effects and non-inferiority for heart rate are desirable, the lack of non-inferiority of dexmedetomidine + sevoflurane combination for arterial blood pressure do not justify the routine use of this combination compared with sevoflurane alone for children with congenital heart disease undergoing cardiac catheterization.     

Effects of exercise training on aerobic fitness in children after open heart surgery

Summary Graded treadmill tests to maximal exercise were given to 24 children 1 year or more after open-heart surgery and to 26 age- and sex-matched controls, before and after 9 weeks of exercise training to test whether or not they could increase their aerobic fitness levels. The corrected cardiac lesions included tetralogy of Fallot, aortic stenosis, transposition of the great arteries and atrioventricular canal (AVC). Maximal exercise variables measured were heart rate (HR), oxygen consumption (VO₂), and workload (stage of exercise and time on treadmill). The results of the pretraining tests indicated that the fitness levels of the 24 patients were significantly less than those of the controls. Of the original groups, 9 controls and 12 patients satisfactorily completed the training (jogging) program. The results of the post-training tests indicated that both the patients and controls significantly improved their fitness levels. Specifically, most subjects improved their maximal workload with little or no increase in maximal HR or VO₂.In conclusion, children after open-heart surgery for complex congenital heart disease can further improve their work capacity by a dynamic exercise program. After training, they are able to do more work at a given VO₂.This project was supported by the Thrasher Research Fund.     

Normality of cardiopulmonary capacity in children operated on to correct congenital heart defects

BACKGROUND: One of the main goals of corrective surgery of congenital heart defects in children is the improvement of quality of life, which in young children is predominantly determined by exercise capacity. It is not known whether this goal can be achieved in school-aged children who have undergone cardiac surgery in infancy. OBJECTIVES: To determine if primary school-aged children who underwent surgery to correct congenital heart defects in infancy are physically as fit as their peers. METHODS: We examined 84 children with congenital heart defects, aged 4 to 11 years, after surgical repair. Fifty-two children had simple defects (ie, atrial or ventricular septal defect, coarctation of the aorta). Thirty-two children had complex defects (ie, tetralogy of Fallot, pulmonary atresia with ventricular septal defect). All patients underwent exercise testing performed on a specially modified bicycle ergometer. Ninety-eight sex- and age-matched healthy children served as the control group. RESULTS: There was no gender difference, either in healthy children or in the group with congenital heart defects, regarding exercise testing and that the healthy children reached a mean +/- SD normalized maximal performance of 2.8 +/- 0.3 W/kg. The same range was found for the children who had undergone surgery to correct simple heart defects. The children operated on to correct complex heart defects showed significantly impaired mean normalized maximal performance, although this tended to be lower in the group that had pulmonary atresia with a ventricular septal defect than in the group with tetralogy of Fallot (mean normalized maximal performance, 1.9 W/kg vs 2.3 W/kg). CONCLUSIONS: The goal of normal exercise capacity in childhood after heart surgery is achieved in those with simple heart defects only. In children with complex heart defects impaired exercise performance persists, depending on the severity of the heart defect and probably on chronotropic incompetence.     

Longitudinal evaluation of cardiopulmonary performance during exercise after bone marrow transplantation in children

OBJECTIVE: Abnormalities in cardiopulmonary performance during exercise have been reported in children after bone marrow transplantation (BMT). We sought to study changes in exercise performance over time in pediatric BMT survivors. STUDY DESIGN: We retrospectively reviewed the results of serial cardiopulmonary exercise tests performed by patients who had undergone BMT at our institution. Four measurements of cardiopulmonary function are reported: maximum cardiac index (MCI), maximal oxygen consumption (Max VO(2)), oxygen consumption at ventilatory threshold (VO(2) at VT), and maximum work (Max Work) performed. A linear mixed-effects model was fitted to assess changes in these parameters over time. RESULTS: Thirty-three patients performed 96 cardiopulmonary exercise tests. MCI and VO(2) at VT were depressed at initial testing and did not change over time. Max VO(2) increased by 4% per year to 69% predicted, and Max Work increased to 77% predicted at 6 years after BMT. CONCLUSIONS: In spite of an impaired cardiovascular response to exercise as indicated by the persistently low MCI, aerobic and physical working capacity increase. Improved Max VO(2) suggests that oxygen extraction at the musculoskeletal level becomes more efficient with recovery from BMT. This may represent a compensatory response to an impaired ability to increase cardiac output.