Prepubescents' ventilatory responses to exercise with reference to sex and body size

Oxygen uptake efficiency slope in 8- to 12-year-old boys and girls

BACKGROUND

Oxygen uptake efficiency slope (OUES) is an objective physiological measure that can be obtained from a standard graded exercise test. However, there is conflicting evidence regarding sex differences in OUES values in children. Therefore, this study investigated potential sex differences in absolute, ratio-scaled, and allometrically scaled OUES in 8.0- to 12.0-year-old children.

METHODS

Retrospective and prospective data of 18 boys and 22 girls were utilized. All participants had undergone familiarization before performing a maximal cycle ergometer test to determine OUES. These values were also ratio-scaled and allometrically scaled to mass and body surface area (BSA). Group differences were tested via independent sample t-tests (or Mann-Whitney U if not normally distributed).

RESULTS

Absolute OUES values (VO2 mL∙min-1/log10VE L∙min-1) were significantly higher in boys compared to girls (1860.8±359.3 vs. 1514.3±212.6). When scaled to mass (VO2 mL∙kg-1∙min-1/log10VE L∙kg-1∙min-1), OUES was no longer significantly different between groups, but when scaled to BSA (VO2 mL∙m-2∙min-1/log10VE L∙m-2∙min-1), OUES was significantly higher in the boys than the girls (1414.4±204.2 vs. 1268.9±134.6). When allometry was applied for mass (OUES/mass0.444) boys had significantly higher value than girls (350.8±46.7 vs. 305.0±31.5).

CONCLUSIONS

The present study demonstrated that boys had greater OUES values scaled to BSA and allometrically scaled to body mass. These findings provide further evidence of sex differences with OUES values in preadolescent children and implies the need for sex-specific reference values prior to using OUES for the assessment of cardiorespiratory pathology in children.

Ventilatory responses at submaximal exercise intensities in healthy children and adolescents during the growth spurt period: a semi-longitudinal study

PURPOSE

To identify the changes of ventilation ([Formula: see text]_E), tidal volume (V_T) and respiratory frequency (fr) at different incremental step test intensities during maturation of children and adolescents.

METHODS

A semi-longitudinal study was conducted on 68 healthy untrained boys and girls aged 11-17 years. The subjects were separated into three distinct age groups. [Formula: see text]_E, V_T and fr parameters were evaluated annually during 3 years by modifying incremental step test intensities according to ventilatory threshold (V_Th) level (30, 60 and 90% of [Formula: see text]O_2max). Absolute and relative values of ventilatory responses were analyzed and compared according to age and developmental phase.

RESULTS

(1) Height, weight, lean body mass and vital capacity increased significantly from 11 to 17 years of age. (2) [Formula: see text]O_2max, [Formula: see text]_E, and V_T increased during maturation even when exercise intensity changed, especially from 11 to 15 years of age. On the other hand, fr showed a decreasing trend.

CONCLUSION

Increases of V_T are the main reason for [Formula: see text]_E increases during maturation of children. fr decreased independently of total body mass during maturation. [Formula: see text]_E.kg^-1 was stable despite intensity variations. V_T.kg^-1 increased significantly from 11 to 15 years then stabilized at 17 years. Lean body mass seems to explain the evolution of V_T.kg^-1 during maturation.

Aerobic Capacity of Preterm Children with Very Low Birth Weight at School Age and its Associated Factors

INTRODUCTION

Respiratory morbidities of preterm infants can cause significant ventilatory impairment thus compromising the aerobic capacity in childhood and adolescence. Therefore, the present study was conducted to evaluate the aerobic capacity in school age preterm children with VLBW and its associated factors.

METHODS

A cross-sectional study was conducted among preterm born with VLBW and term children, both aged 6-9 years. An individualized symptom-limited treadmill testing protocol performed aerobic capacity. Measured variables: oxygen pulse (PuO₂), percentage of maximum heart rate for age (%HR max), tidal volume/inspiratory capacity ratio (TV/IC), oxygen consumption (VO₂) peak, and the ratio of the anaerobic threshold of gas exchange to the predicted percentage of maximum VO₂ (VO₂@LA/%VO₂ max.pred.) were compared between groups. Univariate and multiple linear regression analyses were used to determine the factors associated with aerobic capacity.

RESULTS

Thirty-four preterm and 32 term children were included. Similar VO₂ peak and the other variables were observed. The development of bronchopulmonary dysplasia (BPD) and being obese/overweight was positively associated with %HR max. The Z-score for height/age and birth weight <1000g was positively associated with PuO₂ and peak VO₂, and negatively associated with overweight/obesity and female sex.

CONCLUSIONS

Aerobic capacity was similar in both groups. Sex, development of BPD, birth weight <1000g and factors related to body growth, such as Z-score for height/age and overweight/obesity, were associated with aerobic capacity in preterm children with VLBW.

Ventilatory Limitation of Exercise in Pediatric Subjects Evaluated for Exertional Dyspnea

Purpose: Attribution of ventilatory limitation to exercise when the ratio of ventilation (V˙E) at peak work to maximum voluntary ventilation (MVV) exceeds 0.80 is problematic in pediatrics. Instead, expiratory flow limitation (EFL) measured by tidal flow-volume loop (FVL) analysis – the method of choice – was compared with directly measured MVV or proxies to determine ventilatory limitation.

Methods: Subjects undergoing clinical evaluation for exertional dyspnea performed maximal exercise testing with measurement of tidal FVL. EFL was defined when exercise tidal FVL overlapped at least 5% of the maximal expiratory flow-volume envelope for > 5 breaths in any stage of exercise. We compared this method of ventilatory limitation to traditional methods based on MVV or multiples (30, 35, or 40) of FEV₁. Receiver operating characteristic curves were constructed and area under curve (AUC) computed for peak V˙E/MVV and peak V˙E/x⋅FEV₁.

Results: Among 148 subjects aged 7–18 years (60% female), EFL was found in 87 (59%). Using EFL shown by FVL analysis as a true positive to determine ventilatory limitation, AUC for peak V˙E/30⋅FEV₁ was 0.84 (95% CI 0.78–0.90), significantly better than AUC 0.70 (95% CI 0.61–0.79) when 12-s sprint MVV was used for peak V˙E/MVV. Sensitivity and specificity were 0.82 and 0.70 respectively when using a cutoff of 0.85 for peak V˙E/30⋅FEV₁ to predict ventilatory limitation to exercise.

Conclusion: Peak V˙E/30⋅FEV₁ is superior to peak V˙E/MVV, as a means to identify potential ventilatory limitation in pediatric subjects when FVL analysis is not available.

The Use of a Wheelchair Propulsion Field Test to Determine Peak Heart Rate in Children and Adolescents With Myelomeningocele

PURPOSE

We analyzed the evolution and pattern of heart rate (HR) during the 12-minute wheelchair propulsion field test (WPFT) and compared the peak HR (HR_peak) from the WPFT to the HR_peak obtained in the progressive cardiopulmonary exercise test on arm cranking ergometer (ACT). We aimed to determine if the field test detects the HR_peak consistently and could be used in clinical practice.

METHODS

Eleven wheelchair-using children and adolescents with myelomeningocele (aged 8-15 y) performed a maximal ACT and a 12-minute WPFT. HR was recorded continuously at rest, during each minute of the tests, and at recovery. Mixed analysis of variance was used to compare the variables at rest and peak. Bland-Altman plot and Lin's concordance correlation coefficient were used to show agreement between the tests.

RESULTS

During minute 2 of the WPFT, participants reached 73%-96% of the HR_peak values recorded in the ACT. From minutes 4 to 12, participants reached HR_peak values ranging 86%-109% of the values recorded in the ACT. There is agreement between the ACT and the WPFT tests.

CONCLUSION

WPFT with minimal duration of 4 minutes may be an alternative tool to obtain HR_peak in children and adolescents with myelomeningocele.

A Systematic Review of Reference Values in Pediatric Cardiopulmonary Exercise Testing

Cardiopulmonary exercise testing (CPET) is used for the diagnosis and prognosis of cardiovascular and pulmonary conditions in children and adolescents. Several authors have published reference values for pediatric CPET, but evaluation of their validity is lacking. The aim of this study was to review pediatric CPET references values published between 1980 and 2014. We specifically assessed the adequacy of the normalization methods used to adjust for body size. Articles that proposed references values were reviewed. We abstracted information on exercise protocols, CPET measurements and normalization methods. We then evaluated the studies' methodological quality and assessed them for potential biases. Thirty-four studies were included. We found important heterogeneity in the choice of exercise protocols and in the approach to adjustment for body size or other relevant confounding factors. Adjustment for body size was principally done using linear regression for age or weight. Assessment of potential biases (residual association, heteroscedasticity and departure from the normal distribution) was mentioned in only a minority of studies. Our study shows that contemporary pediatric reference values for CPET have been developed based on heterogeneous exercise protocols and variable normalization strategies. Furthermore, assessment of potential bias has been inconsistent and insufficiently described. High-quality reference values with adequate adjustment for confounding variables are needed in order to optimize CPET's specificity and sensitivity to detect abnormal cardiopulmonary response to exercise.

Cardiorespiratory fitness, respiratory function and hemodynamic responses to maximal cycle ergometer exercise test in girls and boys aged 9-11 years: the PANIC Study

PURPOSE

We aimed to provide comprehensive data on and reference values for cardiorespiratory fitness, respiratory function and hemodynamic responses during and after maximal cycle ergometer test in children.

METHODS

The participants were a population sample of 140 children (69 girls) aged 9-11 years. Heart rate (HR) and systolic blood pressure (SBP) were measured from pre-exercise rest to the end of recovery. Respiratory gases were measured directly by the breath-by-breath method. Peak workload, HR changes, peak oxygen uptake (VO2), peak oxygen pulse (O2 pulse), peak respiratory exchange ratio (RER) and the lowest ratio of ventilation and carbon dioxide output (VE/VCO2) during the exercise test in girls and boys were presented according to their distributions in 5 categories.

RESULTS

HR decreased more during 4-min recovery in boys than in girls (76 vs. 67 beats/min, p < 0.001), whereas SBP decrease was similar in boys and girls (30 vs. 22 mmHg, p = 0.66). Boys had a higher peak VO2 per weight [51.9 vs. 47.6 ml/kg/min, p < 0.001] and per lean mass [67.3 vs. 63.0 ml/kg/min, p < 0.001] than girls. Peak O2 pulse per lean mass was higher in boys than in girls (0.34 vs. 0.31 ml/kg/beat, p < 0.001). There was no difference in the lowest VE/VCO2 during the test between boys and girls (28 vs. 29, p = 0.18).

CONCLUSIONS

The indicators of cardiorespiratory fitness were better in boys than in girls. These data enable the evaluation of cardiorespiratory function during and after maximal exercise test and the detection of children with abnormal values.

Comparison of mechanical ventilatory constraints between continuous and intermittent exercises in healthy prepubescent children

BACKGROUND

The aim of this study was to evaluate the occurrence and severity of mechanical ventilatory constraints in healthy prepubescent children during continuous and intermittent exercise.

METHODS

Twelve prepubescent children (7-11 years old) performed 7 exercises on a treadmill: one graded test for the determination of maximal aerobic speed (MAS), three continuous exercises (CE) at 60, 70, and 80% of MAS and three intermittent exercises (IE), alternating 15 sec of exercise with 15 sec of passive recovery, at 90, 100, and 110% of MAS. During each CE and IE, tidal flow/volume loops were plotted within a maximal flow/volume loop (MFVL) measured at rest before each exercise. Expiratory flow limitation (expFL expressed in %Vt) was defined as the part of exercise tidal volume (Vt) meeting the boundary of MFVL. Breathing strategy was estimated by measuring inspiratory capacity relative to forced vital capacity and tidal volume relative to inspiratory capacity. Other breathing pattern parameters (ventilation VE, Vt, respiratory frequency f) were continuously recorded during exercise.

RESULTS

An "intensity" effect was found for VE during CE (P < 0.001) but not during IE (P = 0.08). The increase in VE was predominantly assumed by an increase in f for both exercise modalities. During each exercise, several children heterogeneously experienced expFL ranging between 10 and 90%Vt. For all exercises, Vt was predominantly regulated by an increase in Vt/IC with no change in IC/FVC from rest to exercise. Finally, no significant "modality" effect was found for mechanical ventilatory constraint parameters (expFL, Vt/IC, and IC/FVC).

DISCUSSION

We could conclude that neither of the modalities studied induced more mechanical ventilatory constraints than the other, but that exercise intensities specific to each modality might be greater sources of exacerbation for mechanical ventilatory constraints.

Expiratory flow limitation during exercise in prepubescent boys and girls: prevalence and implications

The purpose of this study was to compare the prevalence and implications of expiratory flow limitation (EFL) during exercise in boys and girls. Forty healthy, prepubescent boys (B; n = 20) and girls (G; n = 20) were tested. Subjects completed pulmonary function tests and an incremental cycle maximal oxygen uptake (V̇o2max) test. EFL was recorded at the end of each exercise stage using the % tidal volume overlap method. Ventilatory and metabolic data were recorded throughout exercise. Arterial oxygen saturation (SpO2) was determined via pulse oximetry. Body composition was determined using dual-energy X-ray absorptiometry. There were no differences ( P > 0.05) in height, weight, or body composition between boys and girls. At rest, boys had significantly higher lung volumes (total lung capacity, B = 2.6 ± 0.5 liters, G = 2.1 ± 0.5 liters) and peak expiratory flow rates (B = 3.6 ± 0.6 l/s; G = 1.6 ± 0.3 l/s). Boys also had significantly higher V̇o2max (B = 46.9 ± 5.9 ml·kg lean body mass−1·min−1, G = 41.7 ± 6.6 ml·kg lean body mass−1·min−1) and maximal ventilation (B = 49.8 ± 8.8 l/min, G = 41.2 ± 8.3 l/min) compared with girls. There were no sex differences ( P > 0.05) at V̇o2max in VE /Vco2, end-tidal Pco2, heart rate, respiratory exchange ratio, or SpO2. The prevalence (B = 19/20 vs. G = 18/20) and severity (B = 58 ± 7% vs. G = 43 ± 8% tidal volume) of EFL was not significantly different in boys compared with girls at V̇o2max. A significant relationship existed between % EFL at V̇o2max and the change in end-expiratory lung volume from rest to maximal exercise in boys ( r = 0.77) and girls ( r = 0.75). In summary, our data suggests that EFL is highly and equally prevalent in prepubescent boys and girls during heavy exercise, which led to an increased end-expiratory lung volume but not to decreases in arterial oxygen saturation.

Late cardiopulmonary and musculoskeletal exercise performance after repair for total anomalous pulmonary venous connection during infancy

OBJECTIVES

We evaluated cardiopulmonary function at rest and during exercise in children after surgical repair for total anomalous pulmonary venous connection.

BACKGROUND

Long-term assessment of cardiopulmonary function during exercise in children after repair for total anomalous pulmonary venous connection during infancy is limited.

METHODS

Resting lung function and cardiopulmonary function during maximal ramp cycle ergometry were evaluated in 27 patients (age = 11 +/- 4 years, 20 were male). Peak oxygen consumption, ventilatory anaerobic threshold, and physical working capacity were compared with normal reference values. Neurologic assessment included neuromuscular function, inattentiveness, and hyperactivity. Patient- and procedure-related variables were assessed for association with peak oxygen consumption, ventilatory anaerobic threshold, and physical working capacity.

RESULTS

Compared with healthy children, peak oxygen consumption (88% +/- 16% of predicted) and ventilatory anaerobic threshold (91% +/- 21% of predicted) were mildly reduced. Chronotropic impairment was observed in 7 patients (32%). Patients with impaired resting lung mechanics were more likely to have impairment in peak oxygen consumption (P < .05). Breathing reserve was normal. Specific anatomy and all operative factors did not have a significant impact on overall exercise performance. Composite score for fine and gross motor function was associated with lower ventilatory anaerobic threshold (P < .05).

CONCLUSIONS

Exercise performance is mildly impaired at long-term follow-up after total anomalous pulmonary venous connection repair during infancy. Residual pulmonary abnormalities are common and associated with lower exercise performance. Neurologic abnormalities are evident in a subgroup, but the impact on late exercise performance is inconclusive.

Cardiopulmonary responses of asthmatic children to exercise: analysis of systolic and diastolic cardiac function

The aim of this study was to evaluate aerobic exercise capacity, cardiac features and function in a group of asthmatic children who underwent medical treatment. Dynamic exercise testing was done to evaluate aerobic exercise capacity. Echocardiography was performed to identify the effects that asthma-induced pulmonary changes have on respiratory and cardiac function in these patients. The study involved 20 asthmatic children (aged 7-16 years) who were followed at our hospital and 20 age- and sex-matched, healthy control subjects. Sixteen of the asthma cases were moderate and four were severe. All 40 subjects underwent similar series of assessments: multiple modes of echocardiography, treadmill stress testing, pulmonary function testing. The means for forced expiratory volume in 1 sec, forced expiratory flow 25-75%, maximal voluntary ventilation and inspiratory capacity were all significantly higher in the control group. The patient group had significantly lower mean maximal oxygen uptake and mean endurance time than the controls but there were no significant differences between the groups with respect to respiratory exchange ratio or the ventilatory threshold. The control group means for ejection fraction, fractional shortening, left ventricular mass, and left ventricular mass index were significantly higher than the corresponding patient group results. Children with moderate or severe asthma have lower aerobic capacity than healthy children of the same age. The data suggest that most of these children have normal diastolic cardiac function, but exhibit impaired systolic function and have lower LVM than healthy peers of the same age.

Ventilatory efficiency and rate of perceived exertion in obese and non-obese children performing standardized exercise

Sixty children, in the age span 6-17 years originally divided into two groups, matched by age, sex and height--30 obese subjects [15 girls/15 boys; body mass index (BMI) = 27.4 +/- 4.5 m kg-2; ideal body weight (IBW) range = 122-185%] and 30 controls (BMI = 18.8 +/- 2.7 m kg-2) performed incremental treadmill exercise test. Perceived exertion was assessed by means of Category-Ratio Borg scale. The duration of the exercise for the children in the obesity group was significantly shorter than controls (P = 0.010) but obese children have greater absolute values for oxygen uptake (VO2peak ml min-1 = 1907 +/- 671 versus 1495 +/- 562; P = 0.013) and ventilatory variables (VE, VT), which adjusted for body mass decrease significantly (VO2/kg ml min-1 kg-1 = 29.2 +/- 3.8 versus 33.6 +/- 3.5; P < 0.001). Among the various methods for 'normalizing' absolute values of VO2peak for body size, dividing it by body surface area (BSA) yielded the best results (VO2/BSA ml min-1 m-2 = 43.5 +/- 4.6 versus 44.7 +/- 5.6; P = 0.335). The ventilatory efficiency determined either as a slope of VE versus VCO2 or as a simple ratio at anaerobic threshold did not differ between obese and non-obese children in the incremental and recovery periods of exercise. There was a negative correlation of VE/VCO2 slope with age and anthropometric parameters. Obese children rated perceived exertion significantly higher than controls despite the standard workload (Borg score = 6.2 +/- 1.2 versus 5.2 +/- 1.1; P = 0.001). In conclusion, the absolute metabolic cost of exercise is higher in the obesity group compared with the control subjects. Both groups have similar ventilatory efficiency but an increased awareness of fatigue that furthermore limits their physical capacity.

Predicted maximal oxygen uptake in normal Hong Kong Chinese schoolchildren and those with respiratory diseases

To assess the maximum oxygen uptake (V'O2 max) of Hong Kong Chinese children and to explore its association with respiratory illnesses, we conducted the Multistage Fitness Test (MFT), a 20-m shuttle run test, in 1,427 schoolchildren aged between 8-12 years. Information on respiratory symptoms in the previous year, cumulative respiratory illnesses, and habitual physical activities were collected. Spirometry was carried out to derive forced expiratory volume in 1 sec (FEV1). The V'O2max was 30.3 mL x kg( - 1) x min( - 1) for boys, and 28.6-mL x kg( - 1) x min( - 1) for girls; these values were low by Western standards. V'O2max was significantly reduced in children with asthma ( - 1.3 mL x kg( - 1) x min( - 1)) and bronchitis ( - 0.7.mL x kg( - 1) x min( - 1)) when adjusted for other covariates. A significant decrease in FEV1 was also observed in these children. The correlation between V'O2max and FEV1 was significant but weak. Habitual physical activity was an independent predictor of V'O2max, but not of FEV1. The low V'O2 max in Hong Kong children may be explained in part by ethnic differences and possibly a low level of physical activity.

Maximising the clinical use of exercise gaseous exchange testing in children with repaired cyanotic congenital heart defects: the development of an appropriate test strategy

Implicit in deciding upon an exercise test strategy to elucidate cardiopulmonary function in children with congenital heart disease are appropriate application of gas exchange techniques and the significance of the data collected to the specific congenital heart disorder. Post-operative cardiopulmonary responses to exercise in cyanotic disorders are complex and, despite a large body of extant literature in paediatric patients, there has been much difficulty in achieving quality and consistency of data. Maximal oxygen uptake is widely recognised as the best single indicator of cardiopulmonary function and has therefore been the focus of most clinical exercise tests in children. Many children with various heart anomalies are able to exercise to maximum without adverse symptoms, and it is essential that test termination is based on the same criteria for these children. Choosing appropriate, valid indicators of maximum in children with congenital heart disease is beset by difficulties. Such maximal intensity exercise testing procedures have been challenged on the grounds that they do not give a good indication of cardiopulmonary function that is relevant to real life situations. Furthermore, they are prone to much interindividual variability and error in the definition of maximal exertion. Alternative strategies have been proposed which focus upon dynamic submaximal and kinetic cardiopulmonary responses, which are thought to be less dependent on maximal voluntary effort and more suited to the daily activity patterns of children. These methods are also not without problems. Variability in anaerobic threshold measurements and controversy regarding its physiological meaning have been debated. It is recommended that an appropriate cardiopulmonary exercise gas exchange test strategy, which provides clinically useful information for children with cyanotic congenital heart disease, should include both maximal and submaximal data. The inclusion of oxygen uptake kinetics and ventilatory data are encouraged, since they may allow the distinction between a pulmonary, cardiovascular or inactivity related exercise limitation.