Cardiac Structure and Function in Well-Healed Burn Survivors

Attrition of Well-Healed Burn Survivors to a 6-Month Community-Based Exercise Program: A Retrospective Evaluation

The purpose of this study was to evaluate whether burn survivors have lower adherence compared to non-burned control individuals during a 6-month community-based exercise program. In burn survivors, we sought to answer if there was a relation between the size of the burn injury and dropout frequency. Fifty-two burn survivors and 15 non-burned controls (n = 67) were recruited for a 6-month community-based (ie, non-supervised), progressive, exercise training program. During the exercise program, 27% (ie, 4 of the 15 enrolled) of the non-burned individuals dropped out of the study, while 37% (ie, 19 of the 52) of the burn survivors dropped out from the study. There was no difference in the percentage of individuals who dropped out between groups (P = .552). There was no difference in size of the burn injury, expressed as percent body surface area burned (%BSA) between the burn survivors that dropped out versus those who completed the exercise regimen (P = .951). We did not observe a relation between %BSA burned and dropouts (log odds = -0.15-0.01(%BSA), B = -0.01, SE = 0.015, P = .541). There was no effect of %BSA burned on the probability of dropout [Exp (B) = 0.991, 95% CI (0.961, 1.020)] and there were no differences in the percentage of individuals who dropped out of the study based on %BSA burned (χ2(1) = 0.44, P = .51). These data demonstrate that burn survivors have similar exercise adherence relative to a non-burned group and the extent of a burn injury does not affect exercise program adherence.

Evidence for Chronotropic Incompetence in Well-healed Burn Survivors

Due to various pathophysiological responses associated with a severe burn injury, we hypothesized that burn survivors exhibit chronotropic incompetence. To test this hypothesis, a graded peak oxygen consumption (V̇O2peak) test was performed in 94 adults (34 nonburned, 31 burn survivors with 14-35% body surface area grafted, and 29 burn survivors with >35% body surface area grafted). The threshold of 35% body surface area grafted was determined by receiver operating characteristic (ROC) curve analysis. Peak exercise heart rates (HRmax) were compared against age-predicted HRmax within each group. The proportion of individuals not meeting their age-predicted HRmax (within 5 b/min) were compared between groups. Age-predicted HRmax was not different from measured HRmax in the nonburned and moderate burn groups (P = .09 and .22, respectively). However, measured HRmax was 10 ± 6 b/min lower than the age-predicted HRmax in those with a large burn injury (P < .001). While 56 and 65% of individuals in the nonburned and moderate burn group achieved a measured HRmax within 5 b/min or greater of age-predicted HRmax, only 21% of those in the large burn group met this criterion (P < .001). These data provide preliminary evidence of chronotropic incompetence in individuals with severe burn injury covering >35% body surface area.

Cardiac remodeling in well-healed burn survivors after 6 months of unsupervised progressive exercise training

Aerobic exercise is important in the rehabilitation of individuals with prior burn injuries, but no studies have examined whether adult burn survivors demonstrate cardiac remodeling to long-term aerobic exercise training. In this study, we tested the hypothesis that 6 months of progressive exercise training improves cardiac magnetic resonance imaging-based measures of cardiac structure and function in well-healed burn survivors. Secondary analyses explored relations between burn surface area and changes in cardiac structure in the cohort of burn survivors. V̇o2peak assessments and cardiac magnetic resonance imaging were performed at baseline and following 6 months of progressive exercise training from 19 well-healed burn survivors and 10 nonburned control participants. V̇o2peak increased following 6 months of training in both groups (Control: Δ5.5 ± 5.8 mL/kg/min; Burn Survivors: Δ3.2 ± 3.6 mL/kg/min, main effect of training, P < 0.001). Left ventricle (LV) mass (Control: Δ1.7 ± 3.1 g/m2; Burn survivors: Δ1.8 ± 2.7 g/m2), stroke volume (Control: Δ5.8 ± 5.2 mL/m2; Burn Survivors: Δ2.8 ± 4.2 mL/m2), and ejection fraction (Control: Δ2.4 ± 4.0%; Burn Survivors: Δ2.2 ± 4.3%) similarly increased following 6 months of exercise training in both cohorts (main effect of training P < 0.05 for all indexes). LV end-diastolic volume increased in the control group (Δ6.5 ± 4.5 mL/m2) but not in the cohort of burn survivors (Δ1.9 ± 2.7 mL/m2, interaction, P = 0.040). Multiple linear regression analyses revealed that burn surface area had little to no effect on changes in ventricular mass or end-diastolic volumes in response to exercise training. Our findings provide initial evidence of physiological cardiac remodeling, which is not impacted by burn size, in response to exercise training in individuals with well-healed burn injuries.NEW & NOTEWORTHY Aerobic exercise is important in the rehabilitation of individuals with prior burn injuries, but no studies have examined whether adult burn survivors demonstrate cardiac remodeling to long-term aerobic exercise training. In this study, we tested the hypothesis that 6 months of progressive exercise training would improve cardiac magnetic resonance imaging-based measures of cardiac structure and function in well-healed burn survivors. Our findings highlight the ability of exercise training to modify cardiac structure and function in well-healed burn survivors and nonburned sedentary controls alike.

Six months of unsupervised exercise training lowers blood pressure during moderate, but not vigorous, aerobic exercise in adults with well-healed burn injuries

Exercise training reduces cardiovascular disease risk, partly due to arterial blood pressure (BP) lowering at rest and during fixed-load exercise. However, it is unclear whether exercise training can reduce BP at rest and during exercise in adults with well-healed burn injuries. Therefore, the purpose of this investigation was to test the hypothesis that 6 mo of unsupervised exercise training reduces BP at rest and during lower-body cycle ergometry in adults with well-healed burn injuries. Thirty-nine adults (28 with well-healed burn injuries and 11 controls) completed 6 mo of unsupervised, progressive exercise training including endurance, resistance, and high-intensity interval components. Before and after exercise training, we measured BP at rest, during fixed-load submaximal exercise (50 and 75 W), during fixed-intensity submaximal exercise (40% and 70% of V̇o2peak), and during maximal exercise on a lower-body cycle ergometer. We compared cardiovascular variables using two-way ANOVA (group × pre/postexercise training [repeated factor]). Adults with well-healed burn injuries had higher diastolic BP at rest (P = 0.04), which was unchanged by exercise training (P = 0.26). Exercise training reduced systolic, mean, and diastolic BP during fixed-load cycling exercise at 75 W in adults with well-healed burn injuries (P ≤ 0.03 for all), but not controls (P ≥ 0.67 for all). Exercise training also reduced mean and diastolic BP during exercise at 40% (P ≤ 0.02 for both), but not at 70% (P ≥ 0.18 for both), of V̇o2peak. These data suggest that a 6-mo unsupervised exercise training program lowers BP during moderate, but not vigorous, aerobic exercise in adults with well-healed burn injuries.NEW & NOTEWORTHY Adults with well-healed burn injuries have greater cardiovascular disease morbidity and all-cause mortality compared with nonburn-injured adults. We found that exercise training reduced blood pressure (BP) during fixed-load cycling at 75 W and during moderate, but not vigorous, intensity cycling exercise in adults with well-healed burn injuries. These data suggest that 6 mo of unsupervised exercise training provides some degree of cardioprotection by reducing BP responses during submaximal exercise in well-healed burn-injured adults.

Edward F. Adolph Distinguished Lecture. It's more than skin deep: thermoregulatory and cardiovascular consequences of severe burn injuries in humans

Each year, within the United States, tens of thousands of individuals are hospitalized for burn-related injuries. The treatment of deep burns often involves skin grafts to accelerate healing and reduce the risk of infection. The grafting procedure results in a physical disruption between the injured and subsequently debrided host site and the skin graft placed on top of that site. Both neural and vascular connections must occur between the host site and the graft for neural modulation of skin blood flow to take place. Furthermore, evaporative cooling from such burn injured areas is effectively absent, leading to greatly impaired thermoregulatory responses in individuals with large portions of their body surface area burned. Hospitalization following a burn injury can last weeks to months, with cardiovascular and metabolic consequences of such injuries having the potential to adversely affect the burn survivor for years postdischarge. With that background, the objectives of this article are to discuss 1) our current understanding of the physiology and associated consequences of skin grafting, 2) the effects of skin grafts on efferent thermoregulatory responses and the associated consequences pertaining to whole body thermoregulation, 3) approaches that may reduce the risk of excessive hyperthermia in burn survivors, 4) the long-term cardiovascular consequences of burn injuries, and 5) the extent to which burn survivors can "normalize" otherwise compromised cardiovascular responses. Our primary objective is to guide the reader toward an understanding that severe burn injuries result in significant physiological consequences that can persist for years after the injury.

Burn-Induced Cardiac Dysfunction: A Brief Review and Long-Term Consequences for Cardiologists in Clinical Practice

BACKGROUND

Severe burn injury is a specific type of trauma, which induces a unique complex of responses in the body and leads to an extreme increase in stress hormones and proinflammatory cytokines. These hypermetabolic and stress responses are desirable in the acute phase but can persist for several years and lead - due to several mechanisms - to many late complications, including myocardial dysfunction.

METHODS

The databases of PubMed, ScienceDirect, National Institutes of Health (NIH) of the United States, and Google Scholar were searched. Studies relevant to the topic of late cardiovascular dysfunction after burn injury were compiled using key words.

RESULTS

Burn-induced heart disease significantly increases morbidity and mortality and contributes to the reduction in the quality of life of patients after severe burn trauma. A variety of mechanisms causing myocardial dysfunction after burn trauma have been detailed but understanding all of the exact consequences is limited, especially regarding chronic cardiovascular changes.

CONCLUSION

A detailed understanding of the pathophysiology of chronic cardiac changes can contribute to a comprehensive and preventive treatment plan and improve long-term outcomes of burn patients.

Exercise Training Improves Microvascular Function in Burn Injury Survivors

INTRODUCTION

Vasodilator function is impaired in individuals with well-healed burn injuries; however, therapeutic interventions that lessen or reverse this maladaptation are lacking. The purpose of this study was to test the hypothesis that a 6-month community-based exercise training program would increase microvascular dilator function in individuals with well-healed burn injuries, irrespective of the magnitude of the injured body surface area. Further, we hypothesize that macrovascular dilator function would remain unchanged posttraining.

METHODS

Microvascular function (forearm reactive hyperemia), macrovascular function (brachial artery flow-mediated dilation), and the maximal vasodilatory response after ischemic handgrip exercise (an estimate of microvascular remodeling) were assessed before and after exercise training in nonburned control subjects (n = 11) and individuals with burn injuries covering a moderate body surface area (26% ± 7%; n = 13) and a high body surface area (59% ± 15%; n = 19).

RESULTS

Peak vascular conductance and area under the curve during postocclusive reactive hyperemia increased from pretraining to posttraining in control and burn injury groups (both P < 0.05), the magnitude of which did not differ between groups (both P = 0.6). Likewise, the maximal vasodilatory response after ischemic handgrip exercise increased in all groups after exercise training (P < 0.05). Macrovascular dilator function did not differ across time or between groups (P = 0.8).

CONCLUSIONS

These data suggest that a community-based exercise training program improves microvascular function in individuals with well-healed burn injuries, which may be due in part to vascular remodeling.

The benefits of an unsupervised exercise program in persons with well-healed burn injuries within the International Classification of Functioning, Disability and Health (ICF)

Vast improvements in the survival rates following burn injuries has led to a greater number of patients living with a wide range of long-term impairments, activity limitations, and participation constraints. Therefore, long-term care is critical in this clinical population and necessitates appropriate rehabilitation strategies to maximize an individual's overall health. The purpose of this study was to test the hypothesis that the extent to which outcomes within the International Classification of Functioning, Disability, and Health (ICF) framework are improved following 6 months of unsupervised exercise training is influenced by the severity of a burn injury (i.e., percent body surface area injured). Outcome variables representing the dimensions of the ICF, body functions & structure, activity, and participation, were collected pre- and post- 6 months of exercise training in three groups of participants: non-injured control subjects (N = 11), subjects with moderate-level well-healed burn injuries (N = 13, 26 ± 6% body surface area burned), and subjects with high-level well-healed burn injuries (N = 20, 58 ± 15% body surface area burned). Exercise training improved lower extremity strength (changes in peak torque/kg body mass at 90 degrees/sec flexion: 30 ± 5% and extension: 36 ± 4%, p < 0.05) and functional activities (changes in sit to stand: -9 ± 4% and ascend stairs: -4 ± 1%; p < 0.05) in all groups. For outcome variables representing ICF levels of body functions & structure and activity, there were no differences at baseline or improvements made between the groups after training. That said, with the exception of the domain of functional activity (reported 17 ± 34% improvement in the high-level burn cohort, p < 0.05), no changes were revealed in the participation level of ICF indexed by health-related quality of life questionnaires. These findings support the utilization of a 6-month unsupervised exercise training program in the long-term rehabilitation of individuals with burn injuries; that is, improvements in body functions & structure and activity can be achieved with an exercise regimen regardless of the severity of burn injury.

Progressive exercise training improves maximal aerobic capacity in individuals with well-healed burn injuries

Long-term rehabilitative strategies are important for individuals with well-healed burn injuries. Such information is particularly critical because patients are routinely surviving severe burn injuries given medical advances in the acute care setting. The purpose of this study was to test the hypothesis that a 6-mo community-based exercise training program will increase maximal aerobic capacity (V̇o_2max) in subjects with prior burn injuries, with the extent of that increase influenced by the severity of the burn injury (i.e., percent body surface area burned). Maximal aerobic capacity (indirect calorimetry) and skeletal muscle oxidative enzyme activity (biopsy of the vastus lateralis muscle) were measured pre- and postexercise training in noninjured control subjects (n = 11) and in individuals with well-healed burn injuries (n = 13, moderate body surface area burned; n = 20, high body surface area burned). Exercise training increased V̇o_2max in all groups (control: 15 ± 5%; moderate body surface area: 11 ± 3%; high body surface area: 11 ± 2%; P < 0.05), though the magnitude of this improvement did not differ between groups (P = 0.7). Exercise training also increased the activity of the skeletal muscle oxidative enzymes citrate synthase (P < 0.05) and cytochrome c oxidase (P < 0.05), an effect that did not differ between groups (P = 0.2). These data suggest that 6 mo of progressive exercise training improves V̇o_2max in individuals with burn injuries and that the magnitude of body surface area burned does not lessen this adaptive response.