Children with Burn Injury Have Impaired Cardiac Output during Submaximal Exercise

Inter-individual variability of aerobic capacity after rehabilitation exercise training in children with severe burn injury

INTRODUCTION

Severe burn trauma damages resting and exercise cardiac function that may affect long term cardiovascular health. The implementation of rehabilitation exercise training (RET) soon after hospital discharge improves cardiorespiratory fitness; however, it does not fully restore aerobic capacity and presents large inter-individual variability. We tested the hypothesis that the inter-individual variability of aerobic capacity for responders (R) compared to nonresponders (NR) would differ for exercise frequency and intensity.

METHODS

Thirty-three children (11 female, [mean±SD] 12 ± 3 years, 145 ± 18 cm, 40 ± 11 kg, 49 ± 31 BMI percentile) with severe burns (49 ± 15 % total body surface area burned, with 35 ± 22 % third-degree burns) completed a 6-week RET program. Cardiorespiratory fitness (peak VO2) was measured before and after RET. Frequency (session days/week), intensity (% peak heart rate), time (min/session), and volume (min/week) were compared between responders and non-responders. Significance was set at p < 0.05.

RESULTS

Sixty-four percent of the study population improved peak VO2 after RET whereas 36 % showed no improvements. Using a 2-way factorial ANOVA (group [G] × week [WK]), we found that exercise frequency and session time were similar and increased slightly over 6 weeks between R and NR (main effect for WK; P < 0.002). Exercise volume was significantly lower on week 2 for NR compared to R (G × WK interaction, P < 0.028). Exercise intensity over 6-weeks was significantly lower in the NR compared to the R group (G × WK interaction, P < 0.022).

CONCLUSIONS

Exercise intensity and volume may be important contributors for improving the interindividual response to exercise training for peak VO2. These data suggest that the appropriate dose-response requirement for exercise intensity may be > 80 % peak heart rate and exercise volume of > 150 min per week. Further understanding of the exercise prescription will provide insights important for cardiovascular rehabilitation in children with severe burns.

SUBJECT CODE

Inter-individual Variability, Exercise, Pediatrics, Exercise Training.

[Research advances on the application of rehabilitation exercise training in pediatric burn rehabilitation]

The sequelae of pediatric burn seriously affect the physical function and quality of life of children with burns. Rehabilitation exercise training mainly based on aerobic and resistance exercise can effectively alleviate the negative effects. This article reviews the effects of rehabilitation exercise training on cardiopulmonary function, muscle function, and quality of life of children with burns, and introduces the latest rehabilitation exercise training prescription for children with burns based on type, mode, intensity, frequency, and time of exercise, so as to improve the level of rehabilitation treatment for children with burns.

Beyond the acute phase: understanding relationships among cardio-respiratory response to exercises, physical activity levels, and quality of life in children after burn injuries

The long-term cardiorespiratory function in burn-injured children can be jeopardized due to complications brought on by the injury. This study sought to assess the cardio-respiratory responses to maximal exercise in children who sustained a burn injury and explore the relationships among cardio-respiratory response, physical activity levels (PALs), and health-related quality of life (HRQL). Forty-five burn-injured children (age:13.89±2.43 years; duration since burn-injury: 3.13±0.93 years) and 52 age- and gender-matched healthy children (14.15±2.27 years) participated in this study. Both cohorts were evaluated for the maximal exercise capacity [defined by peak oxygen uptake (VO2peak), maximum heart rate (HRmax), minute ventilation (VE), ventilatory equivalent (VEq), respiratory rate (RR), and respiratory exchange ratio (RER)], PALs, and HRQL. The burn-injured children had significantly lower VO2peak (P=.0001) and VE (P=.003) and higher VEq (P<.0001) and RR (P=.007) than their healthy controls, indicating less efficient cardio-respiratory capacity. However, the HRmax (P=.092) and RER (P=.251) were similar. The burn-injured children reported significantly lower PALs (P=.014) and HRQL (P<.0001). The PALs [r (95%CI) = 0.411 (0.132 to 0.624); P = .005] and HRQL [r (95%CI) = 0.536 (0.284 to 0.712); P = .0001] were significantly correlated with the cardio-respiratory capacity represented by VO2peak in burn-injured group. The variations in VO2peak explained ⁓ 17% and 28.7% of the variations in PALs and HRQL, respectively. In conclusion, the cardio-respiratory efficiency of the burn-injured children may remain limited, even up to a few years following the injury. The limited cardio-respiratory capacity account in part for the reduced PALs and HRQL.

Impact of Kinect-based virtual reality training on physical fitness and quality of life in severely burned children: a monocentric randomized controlled trial

BACKGROUND

Pediatric burns lead to persistent and detrimental muscle breakdown, weakness and poor quality of life, so rehabilitation is integral for improving physical and psychological outcomes. However, children with burns are a major challenge to a rehabilitation team. To overcome these challenges, enjoyable and interesting interventions are suggested.

OBJECTIVE

We aimed to determine the impact of the Xbox Kinect on cardiopulmonary fitness, muscle strength, lean mass, quality of life and enjoyment in severely burned children after hospital discharge.

METHODS

This was a randomized controlled trial in a single centre. Participants (n= 40 children) with burn injuries were randomized to the Xbox training group (n=20) or control group (n=20) during 12 weeks. All children received a home programme rehabilitation and Xbox training children received Xbox training. Outcomes included cardiopulmonary fitness (VO2peak), muscle strength (peak torque), lean mass (whole-body and regional), quality of life and physical activity enjoyment at baseline, immediately after hospital discharge, and 12 weeks after the intervention.

RESULTS

The mean (SD) age of the 40 children was 12.97 (1.42) years and total body surface area of burn was 51% (5). The groups did not differ in characteristics at baseline (P < 0.05). After 12 weeks of the intervention, the groups significantly differed in VO2peak, peak torque, quality of life (p<0.001), lean mass and leg lean mass (p<0.05) in favour of Xbox training. The mean difference in VO2peak, peak torque, lean mass and leg lean mass was 3.25 (2.1; 4.5) ml/kg/min, 7.5 (5.8; 9.2) Nm, 1.81 (0.5; 3.1) kg, and 1.1 (0.1; 2.1) kg, respectively. Lean trunk mass did not significantly differ between groups (p=0.07). The Xbox training group reported significantly more enjoyment than did the control group (p<0.001).

CONCLUSION

Xbox Kinect training can increase cardiopulmonary fitness, muscle strength, lean mass and quality of life in burned children. It is one of the most enjoyable, motivated and efficient treatment modalities that should be widely introduced into the pediatric burn rehabilitation.

Quantification of an Exercise Rehabilitation Program for Severely Burned Children: The Standard of Care at Shriners Hospitals for Children®-Galveston

Currently, there are no clear guidelines for the implementation of rehabilitative exercise training (RET) in burned individuals. Therefore, we quantified the training logs for exercise intensity, frequency, and duration of 6 weeks of this program to develop a basic framework for outpatient RET in patients recovering from severe burns. Thirty-three children (11 female, [mean ± SD] 12 ± 3 years, 145 ± 18 cm, 40 ± 11 kg, 49 ± 31 BMI percentile) with severe burns (49 ± 15% total body surface area burned, with 35 ± 22% third-degree burns) completed our 6-week resistance and aerobic exercise training program. Cardiorespiratory fitness (peak VO2), strength, power, and lean body mass (LBM) were measured before and after RET. Outcome measures were analyzed as a relative percentage of values in age- and sex-matched nonburned children (11 female, 12 ± 3 years, 154 ± 20 cm, 49 ± 22 kg, 56 ± 25 BMI percentile). At discharge, burned children had lower LBM (77% of age-sex-matched nonburn values), peak torque (53%), power (62%), and cardiorespiratory fitness (56%). After 6 weeks of training, LBM increased by 5% (82% of nonburn values), peak torque by 18% (71%), power by 20% (81%), and cardiorespiratory fitness by 18% (74%; P < .0001 for all). Quantification of data in exercise training logs suggested that physical capacity can be improved by aerobic exercise training performed at five metabolic equivalents (>70% of peak VO2) at least 3 days/week and 150 minutes/week and by resistance training performed at volume loads (reps × sets × weight) of 131 kg for the upper body and 275 kg for the lower body for 2 days/week. We present for the first time the quantification of our RET and provide clear exercise prescription guidelines specific to children with severe burn injury.

Resting β-Adrenergic Blockade Does Not Alter Exercise Thermoregulation in Children With Burn Injury: A Randomized Control Trial

The objective of this study was to test the hypothesis that propranolol, a commonly prescribed β-blocker to burned children, in combination with exercise-heat stress, increases the risk of heat illness and exercise intolerance. In a randomized double-blind study, propranolol was given to 10 burned children, and placebo was given to 10 additional burned children (matched for TBSA burned; mean ± SD, 62 ± 13%), while nonburned children served as healthy controls. All groups were matched for age and body morphology (11.2 ± 3.0 years; 146 ± 19 cm; 45 ± 18 kg; 1.3 ± 0.4 m2). All children exercised in hot conditions (34.3 ± 1.0°C; 26 ± 2% relative humidity) at 75% of their peak aerobic capacity. At the end of exercise, none of the groups differed for final or change from baseline intestinal temperature (38.0 ± 0.5°C; 0.02 ± 0.01Δ°C·min-1), unburned (37.0 ± 0.6°C) and burned skin temperatures (36.9 ± 0.7°C; nonburn group excluded), heat loss (21 ± 18 W m-2), whole-body thermal conductance (118 ± 113 W m-2), or physiological strain index (5.6 ± 1). However, burn children exercised less than nonburn group (21.2 ± 8.6 vs 30 ± 0.0 min; P < .001) and had a lower calculated exercise tolerance index (1.0 ± 0.0 vs 6.7 ± 4.3; P < .01). Burned children had lower peak heart rates than nonburned children (173 ± 13 vs 189 ± 7 bpm; P < .01), with greater relative cardiac work rates at the end of exercise (97 ± 10 vs 85 ± 11% peak heart rate; P < .01). Resting β-adrenergic blockade does not affect internal body temperature of burned children exercising at similar relative intensities as nonburn children in the heat. Independent of propranolol, a suppressed cardiac function may be associated to exercise intolerance in children with severe burn injury.

Predictability of exercise capacity following pediatric burns: a preliminary investigation

PURPOSE

Describe the course of exercise capacity in pediatric burn patients during the initial 6 months after hospital discharge, and examine whether its recovery can be predicted from burn characteristics, sociodemographic characteristics, and/or prior assessment.

MATERIALS AND METHODS

Exercise capacity was assessed at discharge, and 6 weeks, 3 months, and 6 months after discharge using the Steep Ramp Test (SRT).

RESULTS

Twenty-four pediatric patients with burns affecting 0.1-34% of total body surface area were included. At group level, exercise capacity was low at discharge and did not reach healthy reference values within 6 months, despite significant improvement over time. At individual level, the course of exercise capacity varied widely. Six months after discharge, 48% of participants scored more than one standard deviation below healthy age- and sex-specific reference values. SRT outcomes at 6 weeks and 3 months were the best predictors of exercise capacity 6 months after discharge, explaining, respectively, 76% and 93% of variance.

CONCLUSIONS

Forty-eight percent of participants did not achieve healthy reference values of exercise capacity and were therefore considered "at risk" for diminished functioning. Our preliminary conclusion that early assessment of exercise capacity with the SRT can timely identify those patients, needs to be strengthened by further research.IMPLICATIONS FOR REHABILITATIONPediatric burns can be considered as a chronic medical condition because of the lifelong consequences.Exercise capacity is reduced following- even minor -pediatric burns.Recovery patterns vary widely: some pediatric burn patients achieve healthy levels of exercise capacity without specific intervention, while others do not.The Steep Ramp Test can be used to assess exercise capacity, identifying those "at risk" for adverse outcomes at an early stage.Patients "at risk" should be encouraged to play sports and adopt an active lifestyle.

Burn Injury May Have Age-Dependent Effects on Strength and Aerobic Exercise Capacity in Males

Whether burn injury affects boys and men differently is currently unknown. To test the hypothesis that burned boys have lower exercise capacity and exercise training-induced responses compared with burned men, 40 young boys (12 ± 4 years, 149 ± 20 cm, 46 ± 18 kg) were matched to 35 adult men (33 ± 9 years, 174 ± 10 cm, 84 ± 16 kg) based on extent of burn injury (total body surface area burned, boys 46 ± 14% vs men 47 ± 30, P = .85) and length of hospital stay (boys 33 ± 23 vs men 41 ± 32 days, P = .23). Strength (peak torque) and cardiorespiratory fitness (peak VO2) were normalized to kg of lean body mass for group comparisons. Each group was also compared with normative age-sex matched values at discharge and after an aerobic and resistance exercise training (RET) program. A two-way factorial analysis of covariance assessed interaction and main effects of group and time. We found that boys and men showed similar pre-RET to post-RET increases in total lean (~4%) and fat (7%) mass (each P ≤ .008). Both groups had lower age-sex matched norm values at discharge for peak torque (boys 36%; men 51% of normative values) and peak VO2 (boys: 44; men: 59%; each P ≤ .0001). Boys strength were 13-15 per cent lower than men at discharge and after RET (main effect for group, P < .0001). Cardiorespiratory fitness improved to a greater extent in men (19%) compared with boys (10%) after the RET (group × time interaction, P = .011). These results show that at discharge and after RET, burn injury may have age-dependent effects and should be considered when evaluating efficacy and progress of the exercise program.

Short-term metformin and exercise training effects on strength, aerobic capacity, glycemic control, and mitochondrial function in children with burn injury

Severely burned children experience a chronic state of sympathetic nervous system activation that is associated with hypermetabolic/cardiac stress and muscle wasting. Metformin, a diabetes medication, helps control hyperglycemia in obese diabetic populations, and exercise has been shown to improve exercise strength and aerobic exercise capacity after severe burns. However, whether exercise improves glycemic control in burned children and whether combining exercise and metformin improves outcomes to a greater degree than exercise alone are unknown. We tested the hypothesis that a 6-wk exercise program combined with short-term metformin administration (E + M) improves aerobic and strength exercise capacity to a greater degree than exercise and placebo (E), while improving glucose tolerance and muscle metabolic function. We found that, before exercise training, the metformin group compared with the placebo group had attenuated mitochondrial respiration (pmol·s^-1·mg^-1) for each state: state 2 (-22.5 ± 3), state 3 (-42.4 ± 13), and oxphos (-58.9 ± 19) ( P ≤ 0.02, M vs. E + M group for each state). However, in the E + M group, exercise increased mitochondrial respiration in each state ( P ≤ 0.05), with respiration being comparable to that in the E group (each P > 0.05). In both groups, exercise induced comparable improvements in strength (change from preexercise, Δ1.6 ± 0.6 N-M·kg^LBM) and V̇o_2peak (Δ9 ± 7 mlO₂·kg^LBM) as well as fasting glucose (Δ19.3 ± 13 mg·dl) and glucose AUC (Δ3402 ± 3674 mg·dl^-1·min^-1), as measured by a 75-g OGTT (all P ≤ 0.03). Exercise reduced resting energy expenditure in E + M (Δ539 ± 480 kcal/24 h, P < 0.01) but not E subjects ( P = 0.68). Both groups exhibited reduced resting heart rate (Δ30 ± 23 beats/min, P ≤ 0.02). These data indicate that short-term metformin combined with exercise provides no further improvement beyond that of exercise alone for strength, exercise capacity, and glycemic control.

Children with severe burns display no sex differences in exercise capacity at hospital discharge or adaptation after exercise rehabilitation training

BACKGROUND AND OBJECTIVE

Females have a 50% increased risk of death from burn injury compared to males. However, whether exercise capacity and exercise induced training adaptations differ between burned boys and girls is unknown. This project tested the hypothesis that girls with burns have lower exercise capacity and different exercise induced training adaptations.

METHODS

Twenty-five girls were matched to 26 boys (mean, 95%CI; years 13 [12,14], cm 151 [143,161], kg 54 [45,63]; each P>0.05) for burn injury (% total body surface area burn, 54 [45,62]; P=0.82). Lean body mass (LBM), strength (peak torque) and cardiorespiratory fitness (peak VO₂) were normalized to kg LBM and compared as a percentage of age-sex matched non-burned children (n=26 boys, years 13 [12,14]; n=25 girls, years 13 [12,14]) at discharge (DC) and after aerobic and resistance rehabilitation exercise training (RET).

RESULTS

Using a 2-way factorial ANOVA (group×time), we found both groups had similar 11% change in LBM (87.3% of non-burned values [82.2,92.3]) and after the RET (92.8% [87.2,98.3]; main effect, time P<0.0001). Peak torque increased similarly by 16% in both groups (% of age-sex matched non-burned DC, 55.9 [51.3,60.5]; after RET, 77.5 [72.1,82.9]; main effect, time P<0.0001). Likewise, peak VO₂ increased in both groups by 15% (% of age-sex matched non-burned DC, 56.8 [52.4,61.2] to RET, 72.2 [67.6,76.8]; main effect, time; P<0.0001). Burned children exercise at greater percentage of their peak VO₂ and peak HR compared to non-burned children (Interaction, group×time, P<0.0001).

CONCLUSION

The burn injury does not have sex-dependent effects on LBM or exercise capacity in severely burn injured children. Differences in relative peak VO₂ and peak HR suggest the need for burn specific exercise programs for improving the efficacy of a rehabilitation program.