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Pulmonary function, exercise capacity and physical activity participation in adults following burn
burns 37 (2011) 1326–1333
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Pulmonary function, exercise capacity and physical activity participation in adults following burn C.E. Willis a, T.L. Grisbrook a, C.M. Elliott b, F.M. Wood c, K.E. Wallman a, S.L. Reid a,* a
School of Sport Science, Exercise and Health, The University of Western Australia, 35 Stirling Hwy, Crawley, Perth, 6009 Western Australia, Australia b School of Paediatrics and Child Health, The University of Western Australia, Perth, Western Australia, Australia c Royal Perth Hospital Burns Unit, Perth, Western Australia, Australia
article info
abstract
Article history:
Purpose: To determine the relationship between pulmonary function, aerobic exercise
Accepted 24 March 2011
capacity and physical activity participation in adults following burn. Methods: Eight burn injured males aged 20–55 years (%TBSA 33.3 18.7, 5.1 years 1.8 post
Keywords:
injury), and 30 healthy adult controls participated. Pulmonary function was assessed during
Aerobic exercise
rest via spirometry. A graded exercise test measuring peak oxygen consumption (VO2peak)
Oxygen saturation
and oxygen saturation (SpO2) was conducted, and physical activity was assessed via the
Physical Activity
Older Adult Exercise Status Inventory (OA-EI).
Pulmonary function
Results: No significant correlation was observed between resting pulmonary function, aerobic capacity and physical activity participation for burn injured patients or controls. Two burn injured patients presented with obstructive ventilatory defects, and one displayed a restrictive ventilatory defect. Burn injured patients had a significantly lower VO2peak ( p < 0.001) and time to fatigue ( p = 0.026), and a greater degree of oxygen desaturation ( p = 0.063, Effect Size = 1.02) during a graded exercise test. Burn injured patients reported significantly less participation in leisure-related activity > 9 METs ( p = 0.01), and significantly greater participation in work-related activity ( p = 0.038), than healthy controls. Conclusion: Compromised lung function, decreased aerobic capacity and reduced participation in leisure-related physical activity may still exist in some adults, even up to 5 years post injury. Limitations and long term outcomes of cardiopulmonary function and physical fitness need to be considered in the prescription of exercise rehabilitation programmes following burn. # 2011 Elsevier Ltd and ISBI. All rights reserved.
Burn injuries is a catastrophic event that can result in significant impairments to physical function and health [1]. The increase in the survival rate following burn injuries has resulted in a greater number of patients with extensive functional impairments, activity limitations and participation restrictions living beyond the acute phase of injury [2]. As a result, the primary concern of burn rehabilitation has shifted from survival issues, to maximising functional outcome and quality of life [3]. * Corresponding author. Tel.: +61 8 6488 8781; fax: +61 8 6488 1039. E-mail address: [email protected] (S.L. Reid). 0305-4179/$36.00 # 2011 Elsevier Ltd and ISBI. All rights reserved. doi:10.1016/j.burns.2011.03.016
There is growing evidence that the pathophysiological responses that occur immediately or early after burn injuries can affect the long term outcome of severely injured patients [4]. Pulmonary function can be compromised as a result of complications caused by smoke inhalation, direct thermal damage to the respiratory tract, pulmonary oedema and respiratory tract infection [5]. It has been documented that patients who encounter acute lung injury are at further risk of
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long term respiratory complications from the combination of injury, intubation, infection and chronic inflammation [6], having been reported in both children [7] and adults [5]. Compromised pulmonary function and decreased functional capacity indicate the need for rehabilitative interventions to target all aspects of physical function and health in this population [2]. Current burn rehabilitation strategies aim to assist an individual in achieving optimal function and independence, with the ultimate goal being community reintegration [8]. Exercise of various forms is a common component of rehabilitation treatments following burn injuries [9], as patients may experience increased skeletal muscle catabolism, which can lead to a loss of lean body mass, decreased aerobic capacity and decreased functional ability [10]. As a result, the inclusion of aerobic training is increasingly being recommended as a fundamental component of the multidisciplinary rehabilitation programmes [2,11–14]. Physiological insults that occur as a result of thermal injury may limit the patient’s aerobic capacity [15]. Previous research investigating limitations of the endurance capabilities of paediatric burn survivors is inconclusive [15,16]. One report suggests that children with burns were limited in terms of exercise endurance [15], while another reports no effect of the burn injury on exercise tolerance in children and suggests that even extensive injuries are compatible with normal levels of activity in these patients [16]. However, there is with limited literature available in reference to the adult burns population [12]. Cardiopulmonary complications resulting from burn and smoke inhalation injury can limit the body’s ability to meet the energy needs required during exercise, which can further contribute to decreased aerobic capacity [16] and reduced participation in physical activity. While it is well established that respiration and pulmonary function generally do not limit maximal oxygen consumption in healthy individuals [17–19], endurance exercise has been proposed to be limited by respiration in children recovering from burn and inhalation injuries, even up to 2.5 years following the initial injury [15]. Encouragingly, Suman et al. reported improvements in pulmonary function following a 12-week exercise program in children with severe burns [2]. Significant improvements were also reported in both treadmill time to fatigue and VO2peak following exercise training [2]. With little information relating to adults available – is it possible that impairments in resting respiratory function impact the ability of burn injured adults to perform activities that involve aerobic exercise? The positive relationship between exercise and health is well recognised, with associated benefits between exercise and physical function widely accepted by medical professionals. However, low physical work capacity is a major obstacle in allowing burn injured patients to engage in physical activity [2]. In addition, compromised pulmonary function may contribute to increased fatigue and loss of stamina [20]. Although conflicting data exists in healthy individuals [21–23], it is well documented that physical activity has significant benefits for pulmonary function in patient populations characterised by an underlying pulmonary disease [2,24,25], which may also be true for burn injured adults. While decreased physical activity [26] and compromised pulmonary function [5] have been independently reported in long-term survivors with burn injuries, it is
yet to have been established whether a relationship exists between these parameters, or how these factors may impact aerobic capacity. Despite the extensive amount of literature regarding the impairment of the structure and function of the cardiopulmonary system following severe burn injuries, there has been minimal research pertaining to the long term effect of these impairments on patients’ exercise tolerance and physical activity participation. To restore all aspects of physical function, fitness and health, the functional limitations of the pulmonary system need to be quantified to ensure the appropriate prescription of exercise rehabilitation for this population. Accordingly, this study aimed to assess pulmonary function in relation to aerobic exercise capacity and physical activity participation in adult patients following burn injury. It was hypothesised that burn injured patients would display compromised pulmonary function, reduced physical activity levels and a reduced aerobic exercise capacity when compared to matched healthy controls.
1.
Methods
1.1.
Participants
Eight males who had sustained a burn injury and thirty healthy male controls were recruited for this study (Table 1). Burn injured participants were recruited from via outpatient services at Royal Perth Hospital. Patients who met the inclusion criteria (aged between 20 and 55 years, had sustained an injury of greater than 15% total body surface area (TBSA defined using the Rule of Nines method [3]) and were at least 1 year post injury) were contacted via telephone and invited to participate in the study. Exclusion criteria included open or unhealed wounds or presence of neurological deficit. Apart from the consequences of the burns trauma, individuals were healthy. Characteristics of individual burn injured participants are displayed in Table 2. Control participants were recruited via advertising leaflets. The sample of 30 healthy controls were matched based on age, height and body mass index (BMI) with the burn injured participants. All healthy control participants were asymptomatic, lifelong nonsmokers, with no past or present respiratory disease that may have affected pulmonary function [27].
1.2.
Procedures
Human Ethics approval was obtained from the University of Western Australia’s (UWA) Human Research Ethics Committee and participants provided written consent.
Table 1 – Demographics of burned patients (N = 8) and healthy control participants (N = 30) (mean W standard deviation).
Age (years) Height (cm) Body mass (kg) BMI (kg/m2)
Burn
Control
37.7 11.6 178.7 7.7 80.6 11.3 25.2 2.4
32.9 7.9 182.5 7.0 81.0 10.1 24.3 2.7
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Table 2 – Characteristics of burn injured patients (N = 8). Age (years)
TBSA (%)
Time post Ventilated Inhalation burn (years) (days) injury (Y/N)
B 37.7 11.6 33.3 18.7 5.1 1.8 Individual patient characteristics 75 2.1 B1 24.0
5.6 7.2 21
Y
B2 44.0
30
7.0
7
Y
B3 32.0
36
6.6
0
N
B4 B5 B6 B7
55.0 42.1 46.8 37.3
22 18 35 35
5.3 4.7 3.0 7.1
0 1 5 10
N Y Y Y
B8 20.8
15
4.8
1
N
Location of burn
Torso, face, bilateral upper and lower limb Torso, face, neck, bilateral upper limb Back, face, bilateral upper and lower limb Torso, bilateral upper limb Face, neck, arm (R), thigh (R) Torso, bilateral upper limb Face, neck, bilateral upper limb Neck, bilateral upper limb, knee (R)
Burn depth Smoker Medication (S/PT/FT) (# per day)
FT
12
Nil
FT
–
Nil
FT/PT
–
Nil
S/PT S/PT FT/PT FT
– – 4 –
Nil Nil LIPITOR Nil
FT
–
Nil
TBSA, total body surface area; Y, yes; N, no; R, right; S, superficial; PT, partial thickness; FT, full thickness. B: Group mean (SD) burn injured patients. B1–B8: Individual patient characteristics.
1.2.1.
Pulmonary function assessment
Spirometry measures how an individual inhales or exhales volumes of air as a function of time [28]. In accordance with the American Thoracic Society (ATS), forced vital capacity (FVC) and forced expiratory volume (FEV1.0) were measured at rest from a series of forced expiratory curves [28]. Participants completed the spirometry assessment in the standard seated position using a portable spirometer (Datospir Micro A, Sibelmed, Spain), with a nose clip attached performing three acceptable efforts. Standardised instruction was given and correct technique was demonstrated before the completion of the FVC manoeuvre [28]. The largest FVC and FEV1.0 for each participant were recorded after examining all values, even if they did not come from the same trial [28]. Pulmonary function results were expressed as both observed values and as a percentage of the predicted value [(observed/predicted) 100] [29]. Lower limits of normal (LLN) were derived from the prediction equations to produce the lower 5% tolerance limits [29,30]. Maximum voluntary ventilation (MVV) was calculated indirectly from FEV1.0 values (FEV1.0 37.5) [30,31].
1.2.2.
Graded exercise test
Participants completed a standardised graded exercise test (GXT) using the Bruce protocol [32] to assess aerobic capacity. The Bruce protocol is the most widely employed treadmill protocol used to assess maximal oxygen uptake in clinical populations [35], with both the speed and the inclination grade of the treadmill increased incrementally every 3 min. At the conclusion of each 3-min stage heart rate was recorded, and ratings of perceived exertion (RPE) were measured using the Borg scale [33] in order to assess the participant’s subjective feeling of effort. Communication with participants was continuous, both to encourage a maximal effort and to ensure they were not experiencing any difficulties. The test was terminated once participants indicated that they could no longer continue [34]. During the GXT, expired air was continuously analysed for O2 and CO2 concentrations using Ametek oxygen analysers (Applied Electrochemistry, SOV S-3A/1, Pittsburgh, PA) and
carbon dioxide analysers (Applied Electrochemistry, COV CD3A, Pittsburgh, PA). The gas analysers were calibrated prior to and verified after each exercise test using a certified gravimetric beta-grade gas mixture (BOC gases, Chatswood, Australia). Ventilation was measured with a Morgan ventilometer Mark II 225A (Morgan, Kent, United Kingdom), which was calibrated pre-exercise and verified post-exercise using a 1-l syringe in accordance with manufacturer’s instructions. The sum of the four highest consecutive 15 s VO2 values was recorded as the participants’ VO2peak.
1.2.3.
Arterial oxygen saturation (SaO2) assessment
Pulse oximetry was utilised to provide a continuous estimate of the oxyhaemoglobin saturation of arterial blood. Participants were fitted with a finger probe (Prince-100H wrist oximeter, Shenzhen Creative Industry Co. Ltd., China) to determine arterial oxygen saturation (SpO2). Continuous oxygenation data was taken at 1-s intervals from the finger probe, and was simultaneously uploaded to a wrist watch worn by the participants during the GXT.
1.2.4. Physical activity quantification assessment: Older Adult Exercise Status Inventory (OA-ESI) The OA-ESI is a questionnaire designed to assess the frequency, duration, type and intensity of a wide range of physical activities performed over a seven day period that do not include sitting or lying down [35]. The OA-ESI is scored by multiplying the total minutes of a specific activity performed by the appropriate MET (basal metabolic unit) value to attain gross kilocalorie expenditure for the week.
1.3.
Data analysis
Within group correlations were conducted to determine a relationship between measures of pulmonary health, aerobic fitness and physical activity habits in both burn injured patients and healthy individuals. Independent t-tests were used assess the differences between measures of pulmonary health, aerobic fitness and physical activity habits of burn
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injured patients compared with healthy controls. The alpha level was set to p 0.05. Cohen’s d effect sizes (ES) and thresholds (<0.5, small; 0.5–0.79, moderate; >0.8, large) were also used to identify the magnitude in the difference in mean values of performance scores between healthy control participants and burn injured patients [42]. Only moderate and large ES were reported in the analysis of results.
2.
Results
No significant differences between the healthy males (CON) and burn injured patients (B) were identified for any demographic characteristics (Table 1).
2.1.
Pulmonary function assessment
2.1.1.
Spirometry
Burn injured patients had significantly lower FEV1.0 values (3.90 0.67 L s 1) than that of the healthy control group (4.76 0.75 L s 1) (t(36) = 2.96, p = 0.005, ES = 1.21) (Table 3). There was no significant difference observed for the FEV1.0/ FVC ratio or FVC between groups, however a moderate effect size (ES = 0.75) was observed for FVC. When expressed as a percentage of the predicted value (specific to individual gender, age and height), burn patients displayed significantly lower percentage predicted FEV1.0 values (89.12 8.96%), compared to that of the control group (101.46 13.31%) (t(36) = 2.46, p = 0.019, ES = 1.09). Following the analysis of individual lower limits of normal of FEV1.0/FVC (%), two of the eight burn injured patients (B2 and B3) exhibited ratios below their 5% tolerance limit, indicative of an obstructive ventilatory defect (Table 3). Furthermore, one patient (B6) displayed an FVC < 80% of the predicted value, suggestive of a restrictive ventilatory defect. Predicted MVV differed significantly between groups (t(36) = 2.96, p = 0.005, ES = 1.58), with burn patients showing considerably lower values (146.16 7.49 L min 1) than that of healthy controls (178.43 27.94 L min 1).
2.2.
Assessment of aerobic exercise tolerance
2.2.1.
Graded exercise test (GXT)
Significant differences were observed in peak oxygen consumption (VO2peak) (t(36) = 4.86, p < 0.001, ES = 1.98) and time to fatigue on a GXT (t(36) = 2.32, p = 0.026, ES = 0.91) between groups (Table 4). Burn injured patients displayed a significantly lower VO2peak (36.9 7.0 ml kg 1 min 1) and time to fatigue compared to healthy controls (12.2 2.3 min), (51.4 7.6 ml kg 1 min 1; 14.2 2.1 min). While burn patients reported a significantly lower RPE (17 1.9) compared to the healthy control group (18.8 0.8) (t(7.7) = 2.74, p = 0.027, ES = 1.23), final scores for both groups represented an effort that rated as ‘Very Hard’. No significant difference was observed in resting heart rate (t(36) = 0.20, p = 0.984) or maximum heart rate (t(36) = 1.75, p = 0.088, ES = 0.65) between the groups.
2.2.2.
Arterial oxygen saturation
Resting SpO2 levels were all within the normal range (97–99%) [43] (Table 4). Although no significant difference was observed between groups in SpO2 values at VO2peak (t(7.7) = 2.17, p = 0.063), a large effect size was detected (ES = 1.02). Furthermore, SpO2 values in three patients (B2, B3 and B7) were recorded to drop below 80% at VO2peak. SpO2 did not return to resting levels within the standardised recovery time (120 s) for five of the eight burned patients (%SpO2 94 3.9), with these participants assigned the maximum ‘time to recover’ result of 120 s. The SpO2 values of burn injured patients took significantly longer to return to, and remain stable at, normal saturation levels (110.5 20.8 s) than did the healthy controls (85.9 23.7 s) following exercise (t(36) = 2.66, p = 0.012, ES = 1.10).
2.3.
Reported physical activity
2.3.1.
OA-ESI
There was no significant difference in total physical activity between burn injured patients (3085 1749.1 kcal) and
Table 3 – Mean (WSD) observed spirometric parameters, percentage of predicted values and LLN for burn injured patients (N = 8) and healthy controls (N = 30). FEV1.0 (L s 1) % Predicted Control Burn Individual B1 B2 B3 B4 B5 B6 B7 B8
4.76 0.75 3.90 0.67* patient data 4.02 4.30 4.93 3.89 3.60 2.70 3.45 4.29
LLN (L s 1)
101.46 13.31 89.12 8.96* 85.62 97.10 100.8 88.00 96.70 74.20 80.90 89.64
FVC (L)
% Predicted LLN FEV1.0/FVC (L) (%)
5.93 0.98 102.28 12.59 5.12 1.17 94.39 14.6 3.89 3.63 4.09 3.62 2.92 2.84 3.46 3.99
4.94 6.73 6.71 5.43 4.39 3.27 4.58 4.92
89.59 119.51 110.50 91.47 95.51 72.23 87.78 88.59
Control: group mean (SD) healthy control participants. Burn: group mean (SD) burn injured patients. B1–B8: Individual patient observed values. All predicted values and equations for LLN derived from Gore et al. [29]. * Significance at p < 0.05 level. ** Significance at p < 0.01 level.
4.48 4.60 5.04 4.90 3.56 3.49 4.18 4.52
% Predicted LLN (%) MVV (L min 1)
80.56 6.12 77.2 7.49
97.94 7.4 94.59 7.44
81.38 63.89 73.47 71.73 82.03 82.49 75.38 87.20
96.00 80.38 89.53 93.31 100.79 102.43 92.49 101.78
178.43 27.94 146.16 7.49** 77.00 71.74 74.32 69.13 73.65 72.80 73.76 77.93
150.8 161.3 184.9 145.9 135.0 101.3 129.4 160.9
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Table 4 – Mean (WSD) values of physiological variables of burn injured patients (N = 8) and healthy controls (N = 30) obtained from graded exercise test. Resting HR (bpm)
Max HR (bpm)
Control
76.0 12.1
184.5 10.1
Burn
76.1 8.8
177 12.9
VO2peak (ml kg 1 min 1)
Time to fatigue (min)
51.4 7.6 (34.3–64.6) 36.9 7.0** (26.6–46.8)
14.2 2.1 (10.0–19.0) 12.2 2.3** (9.0–16.0)
RPE
SpO2 (Rest) (%)
SpO2 (VO2peak) (%)
Time to recover (s)
18.8 0.8
98.1 0.9
17 1.9*
98.0
92.1 2.9 (84.0–97.0) 86.5 7.2 (78.0–97.0)
85.9 23.7 (34.0–120.0) 110.5 20.8* (60.0–120.0)
HR, heart rate; VO2peak, maximal oxygen consumption; RPE, rate of perceived exertion; SpO2, oxygen saturation measured by pulse oximetry. Significance at p < 0.05 level. ** Significance at p < 0.01 level. *
healthy male controls (3560.9 1970.5 kcal) (Fig. 1). However, burn patients reported significantly higher participation in work-related physical activity (2296.3 1814.2 kcal) compared to the control group (652.3 854.3 kcal) (t(7.9) = 2.49, p = 0.038, ES = 1.12). Additionally, burn injured patients report less participation in leisure activity significantly than that of healthy males (951.3 785.2 kcal) (2916.0 2023.2 kcal) (t(36) = 2.67, p = 0.011, ES = 1.28). No significant difference between participation in mild (B, 1136.3 1806.7 kcal; CON, 569.1 695.1 kcal), moderate (B, 470 941.5 kcal; CON, 418.2 711.4 kcal) or vigorous intensity (B, 1641.3 1389.4 kcal; CON, 2573.8 2103.9 kcal) physical activity was reported between burn injured patients and healthy controls (Fig. 2). However, a moderate ES (ES = 0.52) was observed for physical activity of vigorous intensity. The category of vigorous intensity physical activity was further analysed based on MET values (6.0–8.9 METs, >9.0 METs) (Fig. 2). There was no significant difference between burn (1341.3 1413.5 kcal) and healthy controls patients (1568.7 1736.3 kcal) in participation in vigorous intensity exercise that ranged from 6.0 to 8.9 METs. However, burn injured patients reported significantly less participation in
physical activity > 9 METs (300.0 431.5 kcal) than healthy controls (1028.9 1193.4 kcal) (t(32.3) = 2.7, p = 0.01, ES = 0.81).
2.4.
A moderate positive relationship existed between FEV1.0/FVC and VO2peak (r = 0.427), MVV and VO2peak (r = 0.402) and between FEV1.0/FVC and physical activity (r = 0.410) in burn injured patients, however these results did not reach significance. There was no relationship between measures of pulmonary function, VO2peak and total physical activity participation in the healthy controls. There was however, a significant moderate positive relationship between physical activity of vigorous intensity (>6 MET) and VO2peak in healthy control participants (r = 0.516, p = 0.004). There was no relationship between these variables in burn injured patients (r = 0.102, p = 0.811).
3.
Discussion
This study aimed to assess pulmonary function in relation to aerobic exercise capacity and physical activity participation in adults who had sustained a burn injury. Although no
6000 Burn
5000
Control
4500
ES=0.52
Burn Control
5000
* 4000
3000
*
2000
Energy Expenditure (kcal)
Energy Expenditure (kcal)
Relationships between variables
4000 3500 3000 2500 2000 1500 1000 500
1000
0 0 Total
Work
Leisure
Physical Activity (Type) Fig. 1 – Mean (+SD) physical activity scores for burn injured patients (N = 8) and healthy controls (N = 30) calculated from the OA-ESI. The sum of work and leisure scores calculates total kilocalorie (kcal) expenditure of a typical week.
Mild (<4MET)
Moderate (4 -5.9 MET)
Vigourous (>6 MET)
Physical Activity (Intensity) Fig. 2 – Mean (+SD) physical activity intensity scores for burn injured patients (N = 8) and healthy controls (N = 30) calculated from the OA-ESI. The sum of mild, moderate and vigorous scores calculates the total kilocalorie (kcal) expenditure of a typical week.
burns 37 (2011) 1326–1333
statistically significant relationships were identified between these parameters, compromised pulmonary function, decreased aerobic capacity and reduced participation in vigorous leisure–time physical activity were observed in burn injured patients. Although there was no significant difference in FEV1.0/FVC ratios between burn injured patients and control participants, the evaluation of individual results identified ventilatory defects in three patients. These patients had injuries to 30% TBSA, including burns to the torso. Two of these patients displayed an obstructive ventilatory defect (B2 and B3), one of which had suffered inhalation injury at the time of burn trauma and was ventilated for seven days (B2). A pattern of restrictive ventilatory function was indicated in one patient (B6). Examination of patient records substantiates the likelihood of restrictive abnormalities existing in this patient, due to evidence of inhalation injury, ventilation and a history of an acute respiratory infection while an inpatient. However, as this patient was a smoker at the time of assessment, the abnormalities in pulmonary function cannot be exclusively attributed to the burn. The five patients with no indication of pulmonary dysfunction either displayed burns <30% TBSA, no injury over the torso, and an absence of inhalation injury and/ or ventilation. It is important to note that regardless of whether a disease pattern was suggested by pulmonary function tests (PFTs) in the present study, the pulmonary function values recorded for burn injured patients were distinctly lower than those of matched healthy controls. In contrast to Whitner et al. (1980) and Bourbeau et al. (1996), who reported pulmonary function to have returned to within normal limits between 5 months [5] and 3.8 years [36] post injury, results from this study indicate a more prolonged impairment in pulmonary function may exist in some patients. Significantly lower MVV values were observed in burn injured patients compared to those of healthy controls. Of importance, three patients displayed MVV values below normal limits. Two of these patients also displayed FEV1.0 values below the LLN (one of whom restrictive abnormalities had been proposed from PFTs (B6)). This data is consistent with that of Suman et al., who reported MVV to be significantly lower in burn injured children compared to age matched peers [2]. This is of particular significance, as MVV is reflective of respiratory muscle endurance, and has previously been reported to correlate well with exercise capacity in burn injured children [2]. Although it is well accepted in healthy individuals that pulmonary function does not limit maximal oxygen consumption [18,19], a respiratory limitation to exercise has been reported in the paediatric burns population [15,37]. The current results concur with that of Bourbeau et al. [36], indicating that pulmonary function, as defined by FEV1.0/FVC measured at rest, does not limit exercise tolerance in burn injured adults. Although partial pressure of oxygen (PaO2) was not measured as part of this protocol, the SpO2 values <88% may be suggestive of severe exercise-induced arterial hypoxemia (EIAH), which may impact energy dynamics during exercise. Although burn injured patients displayed normal SpO2 values at rest, the mean percentage saturation for this group dropped to 86.5% when VO2peak was reached compared
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to 92% in the control group. Furthermore, the SpO2 values of three burns patients were recorded to drop below 80% at VO2peak, two of whom also presented with an obstructive ventilatory defect (B2 and B3). Patterns of obstructive pulmonary function in children 2.5 years post burn have been reported to result in a ventilation-perfusion mismatch, both at rest and during a graded exercise test [37]. Thus, the presence of possible EIAH observed in patients of the present study may be reflective of pulmonary impairments at the level of gas exchange. Additionally, as low SaO2 affects the oxygen saturation of tissue [38], impairments of the cardiopulmonary system may have limited the ability of burn patients to meet the energy needs required during maximal exercise. In addition to, and possibly as a result of, the potential severe hypoxemia exhibited at VO2peak, burn injured patients also required a significantly greater amount of time for SpO2 levels to return to resting levels. Of interest, SpO2 did not return to baseline values within the standardised recovery time of 120 s for five patients. Examination of patient records showed evidence of inhalation injury and ventilation in four of these five patients. Of relevance, burn and smoke inhalation injury have been reported to result in widespread necrosis of alveolar epithelium [39], decreasing the surface area available for gas exchange. Furthermore, mechanical ventilation can result in the overstretching of non-occluded alveoli, contributing to additional tissue injury and alterations in the gas exchange process [40]. Therefore, sufficient recovery time between exercise efforts may need to be considered in the adult population, to allow for adequate re-saturation of arterial blood, potentially delaying the onset of fatigue. Decreased aerobic capacity is increasingly being recognised as a common sequelae following burn [12]. Results from this study demonstrate that aerobic capacity, as defined by VO2peak and time to fatigue on a GXT, was significantly lower in burn injured patients. This is of particular concern, as low cardiorespiratory fitness is a health-related concern for all people [41], whether or not they have a major burn. Encouragingly, there was no difference between the groups in terms of total physical activity, suggesting that despite their injuries, adults who have sustained a burn are able to remain as physically active as healthy males of the same demographics. However, burn injured patients reported significantly less participation in leisure-related physical activity than the control group. Therefore, the reduction in aerobic capacity potentially reflects their significantly lower participation in high intensity, leisure-related exercise (>9 METs e.g. jogging, competitive team sports). The significant, positive relationship between participation in vigorous intensity physical activity and VO2peak observed within the healthy control group adds further support to this contention.
3.1.
Clinical implications for exercise prescription
Cardiopulmonary exercise testing identifies patterns of cardiovascular and respiratory abnormalities and limitations during exercise, offers an objective determination of functional capacity and exercise tolerance, and provides information to be used in designing an exercise rehabilitation program in burn injured individuals [42]. As shown by the results of this study, physiological impairments and functional limitations
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following burn need to be considered in the prescription of frequency, intensity, mode and duration of aerobic exercise. Aerobic exercise three times a week for 20–40 min at 70–85% VO2peak over 12 weeks has been reported to improve pulmonary function and exercise tolerance in burn injured children [2]. Promoting participation in physical activity in adults beyond the acute phase of burn could assist in improving long term impairments in pulmonary function and low aerobic capacity that may exist in these patients, potentially enhancing quality of life. Ideally, SpO2 should be monitored to assess the degree of arterial desaturation and the severity of any impairment, which may help to determine the effectiveness of exercise interventions in adults who have sustained a burn. Although prolonged exercise at moderate intensities only very rarely causes EIAH in healthy males [43], significant desaturation during submaximal exercise has been reported in females [44]. Therefore, progressive interval training should be considered in the aerobic exercise prescription of burn injured adults, as this type of exercise includes a recovery component in addition to the training stimulus, which may allow for sufficient recovery of SaO2.
4.
Conclusion
Despite extensive literature detailing structural and functional impairments of the cardiopulmonary system following severe burn injuries, this is one of few studies that have investigated the long term effect of these impairments on exercise tolerance and physical activity participation in these patients. Results from this study demonstrate that compromised pulmonary function may still exist in some individuals, even up to 5 years post injury, which may lead to significant oxygen desaturation during exercise. When compared to a healthy control group, burn injured patients displayed a significantly lower aerobic capacity, and reported significantly less participation in high intensity, leisure-related physical activity. Findings of this research outline specific limitations of the cardiopulmonary system in adults who have sustained a burn, which may need to be considered in the prescription of aerobic exercise to ensure interventions elicit the best possible functional outcome in this patient population.
Conflict of interest statement All authors concur that there are no financial or personal relationships with other people or organisations that may inappropriately influence the content of the work submitted for publication.
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[3] Johnson M, Richard R. Clinical management extra. Partialthickness burns: identification and management. Adv Skin Wound Care 2003;16(4):178–87. [4] Jeschke MG, Chinkes DL, Finnerty CC, Kulp G, Suman OE, Norbury WB, et al. Pathophysiologic response to severe burn injury. Ann Surg 2008;248(3):387. [5] Whitener DR, Whitener LM, Robertson KJ, Baxter CR, Pierce AK. Pulmonary function measurements in patients with thermal injury and smoke inhalation. Am Rev Respir Dis 1980;122(5):731. [6] Cancio LC. Airway management and smoke inhalation injury in the burn patient. Clin Plast Surg 2009;36(4):555–67. [7] Mlcak R, Desai MH, Robinson E, Nichols R, Herndon DN. Lung function following thermal injury in children—an 8year follow up. Burns 1998;24(3):213–6. [8] Spires C, Brian MK, Percival HP. Rehabilitation methods for the burned individual. Phys Med Rehab Clin N Am 2007;18(4):925–48. [9] Esselman PC, Thombs BD, Magyar-Russell G, Fauerbach JA. Burn rehabilitation: state of the science. Am J Phys Med Rehab 2006;85(4):383. [10] Esselman PC. Burn rehabilitation: an overview. Arch Phys Med Rehab 2007;88(12):S3–6. [11] Celis MM, Suman OE, Huang TT, Yen P, Herndon DN. Effect of a supervised exercise and physiotherapy program on surgical interventions in children with thermal injury. J Burn Care Res 2003;24(1):57. [12] de Lateur BJ. Augmented exercise in the treatment of deconditioning from major burn injury. Arch Phys Med Rehab 2007;88:S18–23. [13] Cucuzzo NA, Ferrando A, Herndon DN. The effects of exercise programming vs traditional outpatient therapy in the rehabilitation of severely burned children. J Burn Care Res 2001;22(3):214. [14] Fairclough TP. Outcomes of exercise training for individuals with burn injury: an international classification of functioning approach. In: School of sport science, exercise and health. Perth: University of Western Australia; 2009. [15] Desai MH, Micak RP, Robinson E, McCauley RL, Carp SS, Robson MC, et al. Does inhalation injury limit exercise endurance in children convalescing from thermal injury? J Burn Care Res 1993;14(1):12. [16] McElroy K, Alvarado M, Hayward PG, Desai MH, Herndon DN, Robson MC. Exercise stress testing for the pediatric patient with burns: a preliminary report. J Burn Care Res 1992;13(2):236. [17] Dempsey JA. Is the lung built for exercise? Med Sci Sport Exer 1986;18(2):143. [18] di Prampero PE, Ferretti G. Factors limiting maximal oxygen consumption in humans. Respir Physiol 1990;80(2–3):113– 28. [19] Ferretti G, Di Prampero PE. Factors limiting maximal O2 consumption: effects of acute changes in ventilation. Respir Physiol 1995;99(2):259–71. [20] Latenser BA, Kowal-Vern A. Paediatric burn rehabilitation. Dev Neurorehab 2002;5(1):3–10. [21] Holmen TL, Barrett-Connor E, Clausen J, Holmen J, Bjermer L. Physical exercise, sports, and lung function in smoking versus nonsmoking adolescents. Eur Respir J 2002;19(1):8. [22] MacAuley D, McCrum E, Evans A, Stott G, Boreham C, Trinick T. Physical activity, physical fitness and respiratory function – exercise and respiratory function. Irish J Med Sci 1999;168(2):119–23. [23] Biersteker MWA, Biersteker PA. Vital capacity in trained and untrained healthy young adults in the Netherlands. Eur J Appl Physiol 1985;54(1):46–53. [24] Vogiatzis I, Williamson AF, Miles J, Taylor IK. Physiological response to moderate exercise workloads in a pulmonary
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[35] O’Brien-Cousins S. An Older Adult Exercise Status Inventory: reliability and validity. J Sport Behav 1996;19(4). [36] Bourbeau J, Lacasse Y, Rouleau MY, Boucher S. Combined smoke inhalation and body surface burns injury does not necessarily imply long-term respiratory health consequences. Eur Respir J 1996;9(7):1470. [37] Mlcak RP, Desai MH, Robinson E, McCauley RL, Richardson J, Herndon DN. Increased physiological dead space/tidal volume ratio during exercise in burned children. Burns 1995;21(5):337–9. [38] Sowa MG, Leonardi L, Payette JR, Fish JS, Mantsch HH. Near infrared spectroscopic assessment of hemodynamic changes in the early post-burn period. Burns 2001;27(3):241–9. [39] Nash G, Foley FD, Langlinais PC. Pulmonary interstitial edema and hyaline membranes in adult burn patients: electron microscopic observations. Human Pathol 1974;5(2):149–60. [40] Dreyfuss D, Martin-Lefevre L, Saumon G. Hyperinflationinduced lung injury during alveolar flooding in rats. Effect of perfluorocarbon instillation. Am J Respir Crit Care Med 1999;159(6):1752. [41] Blair SN, Kohl Iii HW, Barlow CE, Paffenbarger Jr RS, Gibbons LW, Macera CA. Changes in physical fitness and all-cause mortality: a prospective study of healthy and unhealthy men. Jama 1995;273(14):1093. [42] Mlcak RP, Suman OE, Herndon DN. Respiratory management of inhalation injury. Burns 2007;33(1):2–13. [43] Dempsey JA, Wagner PD. Exercise-induced arterial hypoxemia. J Appl Physiol 1999;87(6):1997. [44] Harms CA, McClaran SR, Nickele GA, Pegelow DF, Nelson WB, Dempsey JA. Exercise induced arterial hypoxaemia in healthy young women. J Appl Physiol 1998;507(2):619–28.
available at www.sciencedirect.com
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Pulmonary function, exercise capacity and physical activity participation in adults following burn C.E. Willis a, T.L. Grisbrook a, C.M. Elliott b, F.M. Wood c, K.E. Wallman a, S.L. Reid a,* a
School of Sport Science, Exercise and Health, The University of Western Australia, 35 Stirling Hwy, Crawley, Perth, 6009 Western Australia, Australia b School of Paediatrics and Child Health, The University of Western Australia, Perth, Western Australia, Australia c Royal Perth Hospital Burns Unit, Perth, Western Australia, Australia
article info
abstract
Article history:
Purpose: To determine the relationship between pulmonary function, aerobic exercise
Accepted 24 March 2011
capacity and physical activity participation in adults following burn. Methods: Eight burn injured males aged 20–55 years (%TBSA 33.3 18.7, 5.1 years 1.8 post
Keywords:
injury), and 30 healthy adult controls participated. Pulmonary function was assessed during
Aerobic exercise
rest via spirometry. A graded exercise test measuring peak oxygen consumption (VO2peak)
Oxygen saturation
and oxygen saturation (SpO2) was conducted, and physical activity was assessed via the
Physical Activity
Older Adult Exercise Status Inventory (OA-EI).
Pulmonary function
Results: No significant correlation was observed between resting pulmonary function, aerobic capacity and physical activity participation for burn injured patients or controls. Two burn injured patients presented with obstructive ventilatory defects, and one displayed a restrictive ventilatory defect. Burn injured patients had a significantly lower VO2peak ( p < 0.001) and time to fatigue ( p = 0.026), and a greater degree of oxygen desaturation ( p = 0.063, Effect Size = 1.02) during a graded exercise test. Burn injured patients reported significantly less participation in leisure-related activity > 9 METs ( p = 0.01), and significantly greater participation in work-related activity ( p = 0.038), than healthy controls. Conclusion: Compromised lung function, decreased aerobic capacity and reduced participation in leisure-related physical activity may still exist in some adults, even up to 5 years post injury. Limitations and long term outcomes of cardiopulmonary function and physical fitness need to be considered in the prescription of exercise rehabilitation programmes following burn. # 2011 Elsevier Ltd and ISBI. All rights reserved.
Burn injuries is a catastrophic event that can result in significant impairments to physical function and health [1]. The increase in the survival rate following burn injuries has resulted in a greater number of patients with extensive functional impairments, activity limitations and participation restrictions living beyond the acute phase of injury [2]. As a result, the primary concern of burn rehabilitation has shifted from survival issues, to maximising functional outcome and quality of life [3]. * Corresponding author. Tel.: +61 8 6488 8781; fax: +61 8 6488 1039. E-mail address: [email protected] (S.L. Reid). 0305-4179/$36.00 # 2011 Elsevier Ltd and ISBI. All rights reserved. doi:10.1016/j.burns.2011.03.016
There is growing evidence that the pathophysiological responses that occur immediately or early after burn injuries can affect the long term outcome of severely injured patients [4]. Pulmonary function can be compromised as a result of complications caused by smoke inhalation, direct thermal damage to the respiratory tract, pulmonary oedema and respiratory tract infection [5]. It has been documented that patients who encounter acute lung injury are at further risk of
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long term respiratory complications from the combination of injury, intubation, infection and chronic inflammation [6], having been reported in both children [7] and adults [5]. Compromised pulmonary function and decreased functional capacity indicate the need for rehabilitative interventions to target all aspects of physical function and health in this population [2]. Current burn rehabilitation strategies aim to assist an individual in achieving optimal function and independence, with the ultimate goal being community reintegration [8]. Exercise of various forms is a common component of rehabilitation treatments following burn injuries [9], as patients may experience increased skeletal muscle catabolism, which can lead to a loss of lean body mass, decreased aerobic capacity and decreased functional ability [10]. As a result, the inclusion of aerobic training is increasingly being recommended as a fundamental component of the multidisciplinary rehabilitation programmes [2,11–14]. Physiological insults that occur as a result of thermal injury may limit the patient’s aerobic capacity [15]. Previous research investigating limitations of the endurance capabilities of paediatric burn survivors is inconclusive [15,16]. One report suggests that children with burns were limited in terms of exercise endurance [15], while another reports no effect of the burn injury on exercise tolerance in children and suggests that even extensive injuries are compatible with normal levels of activity in these patients [16]. However, there is with limited literature available in reference to the adult burns population [12]. Cardiopulmonary complications resulting from burn and smoke inhalation injury can limit the body’s ability to meet the energy needs required during exercise, which can further contribute to decreased aerobic capacity [16] and reduced participation in physical activity. While it is well established that respiration and pulmonary function generally do not limit maximal oxygen consumption in healthy individuals [17–19], endurance exercise has been proposed to be limited by respiration in children recovering from burn and inhalation injuries, even up to 2.5 years following the initial injury [15]. Encouragingly, Suman et al. reported improvements in pulmonary function following a 12-week exercise program in children with severe burns [2]. Significant improvements were also reported in both treadmill time to fatigue and VO2peak following exercise training [2]. With little information relating to adults available – is it possible that impairments in resting respiratory function impact the ability of burn injured adults to perform activities that involve aerobic exercise? The positive relationship between exercise and health is well recognised, with associated benefits between exercise and physical function widely accepted by medical professionals. However, low physical work capacity is a major obstacle in allowing burn injured patients to engage in physical activity [2]. In addition, compromised pulmonary function may contribute to increased fatigue and loss of stamina [20]. Although conflicting data exists in healthy individuals [21–23], it is well documented that physical activity has significant benefits for pulmonary function in patient populations characterised by an underlying pulmonary disease [2,24,25], which may also be true for burn injured adults. While decreased physical activity [26] and compromised pulmonary function [5] have been independently reported in long-term survivors with burn injuries, it is
yet to have been established whether a relationship exists between these parameters, or how these factors may impact aerobic capacity. Despite the extensive amount of literature regarding the impairment of the structure and function of the cardiopulmonary system following severe burn injuries, there has been minimal research pertaining to the long term effect of these impairments on patients’ exercise tolerance and physical activity participation. To restore all aspects of physical function, fitness and health, the functional limitations of the pulmonary system need to be quantified to ensure the appropriate prescription of exercise rehabilitation for this population. Accordingly, this study aimed to assess pulmonary function in relation to aerobic exercise capacity and physical activity participation in adult patients following burn injury. It was hypothesised that burn injured patients would display compromised pulmonary function, reduced physical activity levels and a reduced aerobic exercise capacity when compared to matched healthy controls.
1.
Methods
1.1.
Participants
Eight males who had sustained a burn injury and thirty healthy male controls were recruited for this study (Table 1). Burn injured participants were recruited from via outpatient services at Royal Perth Hospital. Patients who met the inclusion criteria (aged between 20 and 55 years, had sustained an injury of greater than 15% total body surface area (TBSA defined using the Rule of Nines method [3]) and were at least 1 year post injury) were contacted via telephone and invited to participate in the study. Exclusion criteria included open or unhealed wounds or presence of neurological deficit. Apart from the consequences of the burns trauma, individuals were healthy. Characteristics of individual burn injured participants are displayed in Table 2. Control participants were recruited via advertising leaflets. The sample of 30 healthy controls were matched based on age, height and body mass index (BMI) with the burn injured participants. All healthy control participants were asymptomatic, lifelong nonsmokers, with no past or present respiratory disease that may have affected pulmonary function [27].
1.2.
Procedures
Human Ethics approval was obtained from the University of Western Australia’s (UWA) Human Research Ethics Committee and participants provided written consent.
Table 1 – Demographics of burned patients (N = 8) and healthy control participants (N = 30) (mean W standard deviation).
Age (years) Height (cm) Body mass (kg) BMI (kg/m2)
Burn
Control
37.7 11.6 178.7 7.7 80.6 11.3 25.2 2.4
32.9 7.9 182.5 7.0 81.0 10.1 24.3 2.7
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Table 2 – Characteristics of burn injured patients (N = 8). Age (years)
TBSA (%)
Time post Ventilated Inhalation burn (years) (days) injury (Y/N)
B 37.7 11.6 33.3 18.7 5.1 1.8 Individual patient characteristics 75 2.1 B1 24.0
5.6 7.2 21
Y
B2 44.0
30
7.0
7
Y
B3 32.0
36
6.6
0
N
B4 B5 B6 B7
55.0 42.1 46.8 37.3
22 18 35 35
5.3 4.7 3.0 7.1
0 1 5 10
N Y Y Y
B8 20.8
15
4.8
1
N
Location of burn
Torso, face, bilateral upper and lower limb Torso, face, neck, bilateral upper limb Back, face, bilateral upper and lower limb Torso, bilateral upper limb Face, neck, arm (R), thigh (R) Torso, bilateral upper limb Face, neck, bilateral upper limb Neck, bilateral upper limb, knee (R)
Burn depth Smoker Medication (S/PT/FT) (# per day)
FT
12
Nil
FT
–
Nil
FT/PT
–
Nil
S/PT S/PT FT/PT FT
– – 4 –
Nil Nil LIPITOR Nil
FT
–
Nil
TBSA, total body surface area; Y, yes; N, no; R, right; S, superficial; PT, partial thickness; FT, full thickness. B: Group mean (SD) burn injured patients. B1–B8: Individual patient characteristics.
1.2.1.
Pulmonary function assessment
Spirometry measures how an individual inhales or exhales volumes of air as a function of time [28]. In accordance with the American Thoracic Society (ATS), forced vital capacity (FVC) and forced expiratory volume (FEV1.0) were measured at rest from a series of forced expiratory curves [28]. Participants completed the spirometry assessment in the standard seated position using a portable spirometer (Datospir Micro A, Sibelmed, Spain), with a nose clip attached performing three acceptable efforts. Standardised instruction was given and correct technique was demonstrated before the completion of the FVC manoeuvre [28]. The largest FVC and FEV1.0 for each participant were recorded after examining all values, even if they did not come from the same trial [28]. Pulmonary function results were expressed as both observed values and as a percentage of the predicted value [(observed/predicted) 100] [29]. Lower limits of normal (LLN) were derived from the prediction equations to produce the lower 5% tolerance limits [29,30]. Maximum voluntary ventilation (MVV) was calculated indirectly from FEV1.0 values (FEV1.0 37.5) [30,31].
1.2.2.
Graded exercise test
Participants completed a standardised graded exercise test (GXT) using the Bruce protocol [32] to assess aerobic capacity. The Bruce protocol is the most widely employed treadmill protocol used to assess maximal oxygen uptake in clinical populations [35], with both the speed and the inclination grade of the treadmill increased incrementally every 3 min. At the conclusion of each 3-min stage heart rate was recorded, and ratings of perceived exertion (RPE) were measured using the Borg scale [33] in order to assess the participant’s subjective feeling of effort. Communication with participants was continuous, both to encourage a maximal effort and to ensure they were not experiencing any difficulties. The test was terminated once participants indicated that they could no longer continue [34]. During the GXT, expired air was continuously analysed for O2 and CO2 concentrations using Ametek oxygen analysers (Applied Electrochemistry, SOV S-3A/1, Pittsburgh, PA) and
carbon dioxide analysers (Applied Electrochemistry, COV CD3A, Pittsburgh, PA). The gas analysers were calibrated prior to and verified after each exercise test using a certified gravimetric beta-grade gas mixture (BOC gases, Chatswood, Australia). Ventilation was measured with a Morgan ventilometer Mark II 225A (Morgan, Kent, United Kingdom), which was calibrated pre-exercise and verified post-exercise using a 1-l syringe in accordance with manufacturer’s instructions. The sum of the four highest consecutive 15 s VO2 values was recorded as the participants’ VO2peak.
1.2.3.
Arterial oxygen saturation (SaO2) assessment
Pulse oximetry was utilised to provide a continuous estimate of the oxyhaemoglobin saturation of arterial blood. Participants were fitted with a finger probe (Prince-100H wrist oximeter, Shenzhen Creative Industry Co. Ltd., China) to determine arterial oxygen saturation (SpO2). Continuous oxygenation data was taken at 1-s intervals from the finger probe, and was simultaneously uploaded to a wrist watch worn by the participants during the GXT.
1.2.4. Physical activity quantification assessment: Older Adult Exercise Status Inventory (OA-ESI) The OA-ESI is a questionnaire designed to assess the frequency, duration, type and intensity of a wide range of physical activities performed over a seven day period that do not include sitting or lying down [35]. The OA-ESI is scored by multiplying the total minutes of a specific activity performed by the appropriate MET (basal metabolic unit) value to attain gross kilocalorie expenditure for the week.
1.3.
Data analysis
Within group correlations were conducted to determine a relationship between measures of pulmonary health, aerobic fitness and physical activity habits in both burn injured patients and healthy individuals. Independent t-tests were used assess the differences between measures of pulmonary health, aerobic fitness and physical activity habits of burn
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injured patients compared with healthy controls. The alpha level was set to p 0.05. Cohen’s d effect sizes (ES) and thresholds (<0.5, small; 0.5–0.79, moderate; >0.8, large) were also used to identify the magnitude in the difference in mean values of performance scores between healthy control participants and burn injured patients [42]. Only moderate and large ES were reported in the analysis of results.
2.
Results
No significant differences between the healthy males (CON) and burn injured patients (B) were identified for any demographic characteristics (Table 1).
2.1.
Pulmonary function assessment
2.1.1.
Spirometry
Burn injured patients had significantly lower FEV1.0 values (3.90 0.67 L s 1) than that of the healthy control group (4.76 0.75 L s 1) (t(36) = 2.96, p = 0.005, ES = 1.21) (Table 3). There was no significant difference observed for the FEV1.0/ FVC ratio or FVC between groups, however a moderate effect size (ES = 0.75) was observed for FVC. When expressed as a percentage of the predicted value (specific to individual gender, age and height), burn patients displayed significantly lower percentage predicted FEV1.0 values (89.12 8.96%), compared to that of the control group (101.46 13.31%) (t(36) = 2.46, p = 0.019, ES = 1.09). Following the analysis of individual lower limits of normal of FEV1.0/FVC (%), two of the eight burn injured patients (B2 and B3) exhibited ratios below their 5% tolerance limit, indicative of an obstructive ventilatory defect (Table 3). Furthermore, one patient (B6) displayed an FVC < 80% of the predicted value, suggestive of a restrictive ventilatory defect. Predicted MVV differed significantly between groups (t(36) = 2.96, p = 0.005, ES = 1.58), with burn patients showing considerably lower values (146.16 7.49 L min 1) than that of healthy controls (178.43 27.94 L min 1).
2.2.
Assessment of aerobic exercise tolerance
2.2.1.
Graded exercise test (GXT)
Significant differences were observed in peak oxygen consumption (VO2peak) (t(36) = 4.86, p < 0.001, ES = 1.98) and time to fatigue on a GXT (t(36) = 2.32, p = 0.026, ES = 0.91) between groups (Table 4). Burn injured patients displayed a significantly lower VO2peak (36.9 7.0 ml kg 1 min 1) and time to fatigue compared to healthy controls (12.2 2.3 min), (51.4 7.6 ml kg 1 min 1; 14.2 2.1 min). While burn patients reported a significantly lower RPE (17 1.9) compared to the healthy control group (18.8 0.8) (t(7.7) = 2.74, p = 0.027, ES = 1.23), final scores for both groups represented an effort that rated as ‘Very Hard’. No significant difference was observed in resting heart rate (t(36) = 0.20, p = 0.984) or maximum heart rate (t(36) = 1.75, p = 0.088, ES = 0.65) between the groups.
2.2.2.
Arterial oxygen saturation
Resting SpO2 levels were all within the normal range (97–99%) [43] (Table 4). Although no significant difference was observed between groups in SpO2 values at VO2peak (t(7.7) = 2.17, p = 0.063), a large effect size was detected (ES = 1.02). Furthermore, SpO2 values in three patients (B2, B3 and B7) were recorded to drop below 80% at VO2peak. SpO2 did not return to resting levels within the standardised recovery time (120 s) for five of the eight burned patients (%SpO2 94 3.9), with these participants assigned the maximum ‘time to recover’ result of 120 s. The SpO2 values of burn injured patients took significantly longer to return to, and remain stable at, normal saturation levels (110.5 20.8 s) than did the healthy controls (85.9 23.7 s) following exercise (t(36) = 2.66, p = 0.012, ES = 1.10).
2.3.
Reported physical activity
2.3.1.
OA-ESI
There was no significant difference in total physical activity between burn injured patients (3085 1749.1 kcal) and
Table 3 – Mean (WSD) observed spirometric parameters, percentage of predicted values and LLN for burn injured patients (N = 8) and healthy controls (N = 30). FEV1.0 (L s 1) % Predicted Control Burn Individual B1 B2 B3 B4 B5 B6 B7 B8
4.76 0.75 3.90 0.67* patient data 4.02 4.30 4.93 3.89 3.60 2.70 3.45 4.29
LLN (L s 1)
101.46 13.31 89.12 8.96* 85.62 97.10 100.8 88.00 96.70 74.20 80.90 89.64
FVC (L)
% Predicted LLN FEV1.0/FVC (L) (%)
5.93 0.98 102.28 12.59 5.12 1.17 94.39 14.6 3.89 3.63 4.09 3.62 2.92 2.84 3.46 3.99
4.94 6.73 6.71 5.43 4.39 3.27 4.58 4.92
89.59 119.51 110.50 91.47 95.51 72.23 87.78 88.59
Control: group mean (SD) healthy control participants. Burn: group mean (SD) burn injured patients. B1–B8: Individual patient observed values. All predicted values and equations for LLN derived from Gore et al. [29]. * Significance at p < 0.05 level. ** Significance at p < 0.01 level.
4.48 4.60 5.04 4.90 3.56 3.49 4.18 4.52
% Predicted LLN (%) MVV (L min 1)
80.56 6.12 77.2 7.49
97.94 7.4 94.59 7.44
81.38 63.89 73.47 71.73 82.03 82.49 75.38 87.20
96.00 80.38 89.53 93.31 100.79 102.43 92.49 101.78
178.43 27.94 146.16 7.49** 77.00 71.74 74.32 69.13 73.65 72.80 73.76 77.93
150.8 161.3 184.9 145.9 135.0 101.3 129.4 160.9
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Table 4 – Mean (WSD) values of physiological variables of burn injured patients (N = 8) and healthy controls (N = 30) obtained from graded exercise test. Resting HR (bpm)
Max HR (bpm)
Control
76.0 12.1
184.5 10.1
Burn
76.1 8.8
177 12.9
VO2peak (ml kg 1 min 1)
Time to fatigue (min)
51.4 7.6 (34.3–64.6) 36.9 7.0** (26.6–46.8)
14.2 2.1 (10.0–19.0) 12.2 2.3** (9.0–16.0)
RPE
SpO2 (Rest) (%)
SpO2 (VO2peak) (%)
Time to recover (s)
18.8 0.8
98.1 0.9
17 1.9*
98.0
92.1 2.9 (84.0–97.0) 86.5 7.2 (78.0–97.0)
85.9 23.7 (34.0–120.0) 110.5 20.8* (60.0–120.0)
HR, heart rate; VO2peak, maximal oxygen consumption; RPE, rate of perceived exertion; SpO2, oxygen saturation measured by pulse oximetry. Significance at p < 0.05 level. ** Significance at p < 0.01 level. *
healthy male controls (3560.9 1970.5 kcal) (Fig. 1). However, burn patients reported significantly higher participation in work-related physical activity (2296.3 1814.2 kcal) compared to the control group (652.3 854.3 kcal) (t(7.9) = 2.49, p = 0.038, ES = 1.12). Additionally, burn injured patients report less participation in leisure activity significantly than that of healthy males (951.3 785.2 kcal) (2916.0 2023.2 kcal) (t(36) = 2.67, p = 0.011, ES = 1.28). No significant difference between participation in mild (B, 1136.3 1806.7 kcal; CON, 569.1 695.1 kcal), moderate (B, 470 941.5 kcal; CON, 418.2 711.4 kcal) or vigorous intensity (B, 1641.3 1389.4 kcal; CON, 2573.8 2103.9 kcal) physical activity was reported between burn injured patients and healthy controls (Fig. 2). However, a moderate ES (ES = 0.52) was observed for physical activity of vigorous intensity. The category of vigorous intensity physical activity was further analysed based on MET values (6.0–8.9 METs, >9.0 METs) (Fig. 2). There was no significant difference between burn (1341.3 1413.5 kcal) and healthy controls patients (1568.7 1736.3 kcal) in participation in vigorous intensity exercise that ranged from 6.0 to 8.9 METs. However, burn injured patients reported significantly less participation in
physical activity > 9 METs (300.0 431.5 kcal) than healthy controls (1028.9 1193.4 kcal) (t(32.3) = 2.7, p = 0.01, ES = 0.81).
2.4.
A moderate positive relationship existed between FEV1.0/FVC and VO2peak (r = 0.427), MVV and VO2peak (r = 0.402) and between FEV1.0/FVC and physical activity (r = 0.410) in burn injured patients, however these results did not reach significance. There was no relationship between measures of pulmonary function, VO2peak and total physical activity participation in the healthy controls. There was however, a significant moderate positive relationship between physical activity of vigorous intensity (>6 MET) and VO2peak in healthy control participants (r = 0.516, p = 0.004). There was no relationship between these variables in burn injured patients (r = 0.102, p = 0.811).
3.
Discussion
This study aimed to assess pulmonary function in relation to aerobic exercise capacity and physical activity participation in adults who had sustained a burn injury. Although no
6000 Burn
5000
Control
4500
ES=0.52
Burn Control
5000
* 4000
3000
*
2000
Energy Expenditure (kcal)
Energy Expenditure (kcal)
Relationships between variables
4000 3500 3000 2500 2000 1500 1000 500
1000
0 0 Total
Work
Leisure
Physical Activity (Type) Fig. 1 – Mean (+SD) physical activity scores for burn injured patients (N = 8) and healthy controls (N = 30) calculated from the OA-ESI. The sum of work and leisure scores calculates total kilocalorie (kcal) expenditure of a typical week.
Mild (<4MET)
Moderate (4 -5.9 MET)
Vigourous (>6 MET)
Physical Activity (Intensity) Fig. 2 – Mean (+SD) physical activity intensity scores for burn injured patients (N = 8) and healthy controls (N = 30) calculated from the OA-ESI. The sum of mild, moderate and vigorous scores calculates the total kilocalorie (kcal) expenditure of a typical week.
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statistically significant relationships were identified between these parameters, compromised pulmonary function, decreased aerobic capacity and reduced participation in vigorous leisure–time physical activity were observed in burn injured patients. Although there was no significant difference in FEV1.0/FVC ratios between burn injured patients and control participants, the evaluation of individual results identified ventilatory defects in three patients. These patients had injuries to 30% TBSA, including burns to the torso. Two of these patients displayed an obstructive ventilatory defect (B2 and B3), one of which had suffered inhalation injury at the time of burn trauma and was ventilated for seven days (B2). A pattern of restrictive ventilatory function was indicated in one patient (B6). Examination of patient records substantiates the likelihood of restrictive abnormalities existing in this patient, due to evidence of inhalation injury, ventilation and a history of an acute respiratory infection while an inpatient. However, as this patient was a smoker at the time of assessment, the abnormalities in pulmonary function cannot be exclusively attributed to the burn. The five patients with no indication of pulmonary dysfunction either displayed burns <30% TBSA, no injury over the torso, and an absence of inhalation injury and/ or ventilation. It is important to note that regardless of whether a disease pattern was suggested by pulmonary function tests (PFTs) in the present study, the pulmonary function values recorded for burn injured patients were distinctly lower than those of matched healthy controls. In contrast to Whitner et al. (1980) and Bourbeau et al. (1996), who reported pulmonary function to have returned to within normal limits between 5 months [5] and 3.8 years [36] post injury, results from this study indicate a more prolonged impairment in pulmonary function may exist in some patients. Significantly lower MVV values were observed in burn injured patients compared to those of healthy controls. Of importance, three patients displayed MVV values below normal limits. Two of these patients also displayed FEV1.0 values below the LLN (one of whom restrictive abnormalities had been proposed from PFTs (B6)). This data is consistent with that of Suman et al., who reported MVV to be significantly lower in burn injured children compared to age matched peers [2]. This is of particular significance, as MVV is reflective of respiratory muscle endurance, and has previously been reported to correlate well with exercise capacity in burn injured children [2]. Although it is well accepted in healthy individuals that pulmonary function does not limit maximal oxygen consumption [18,19], a respiratory limitation to exercise has been reported in the paediatric burns population [15,37]. The current results concur with that of Bourbeau et al. [36], indicating that pulmonary function, as defined by FEV1.0/FVC measured at rest, does not limit exercise tolerance in burn injured adults. Although partial pressure of oxygen (PaO2) was not measured as part of this protocol, the SpO2 values <88% may be suggestive of severe exercise-induced arterial hypoxemia (EIAH), which may impact energy dynamics during exercise. Although burn injured patients displayed normal SpO2 values at rest, the mean percentage saturation for this group dropped to 86.5% when VO2peak was reached compared
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to 92% in the control group. Furthermore, the SpO2 values of three burns patients were recorded to drop below 80% at VO2peak, two of whom also presented with an obstructive ventilatory defect (B2 and B3). Patterns of obstructive pulmonary function in children 2.5 years post burn have been reported to result in a ventilation-perfusion mismatch, both at rest and during a graded exercise test [37]. Thus, the presence of possible EIAH observed in patients of the present study may be reflective of pulmonary impairments at the level of gas exchange. Additionally, as low SaO2 affects the oxygen saturation of tissue [38], impairments of the cardiopulmonary system may have limited the ability of burn patients to meet the energy needs required during maximal exercise. In addition to, and possibly as a result of, the potential severe hypoxemia exhibited at VO2peak, burn injured patients also required a significantly greater amount of time for SpO2 levels to return to resting levels. Of interest, SpO2 did not return to baseline values within the standardised recovery time of 120 s for five patients. Examination of patient records showed evidence of inhalation injury and ventilation in four of these five patients. Of relevance, burn and smoke inhalation injury have been reported to result in widespread necrosis of alveolar epithelium [39], decreasing the surface area available for gas exchange. Furthermore, mechanical ventilation can result in the overstretching of non-occluded alveoli, contributing to additional tissue injury and alterations in the gas exchange process [40]. Therefore, sufficient recovery time between exercise efforts may need to be considered in the adult population, to allow for adequate re-saturation of arterial blood, potentially delaying the onset of fatigue. Decreased aerobic capacity is increasingly being recognised as a common sequelae following burn [12]. Results from this study demonstrate that aerobic capacity, as defined by VO2peak and time to fatigue on a GXT, was significantly lower in burn injured patients. This is of particular concern, as low cardiorespiratory fitness is a health-related concern for all people [41], whether or not they have a major burn. Encouragingly, there was no difference between the groups in terms of total physical activity, suggesting that despite their injuries, adults who have sustained a burn are able to remain as physically active as healthy males of the same demographics. However, burn injured patients reported significantly less participation in leisure-related physical activity than the control group. Therefore, the reduction in aerobic capacity potentially reflects their significantly lower participation in high intensity, leisure-related exercise (>9 METs e.g. jogging, competitive team sports). The significant, positive relationship between participation in vigorous intensity physical activity and VO2peak observed within the healthy control group adds further support to this contention.
3.1.
Clinical implications for exercise prescription
Cardiopulmonary exercise testing identifies patterns of cardiovascular and respiratory abnormalities and limitations during exercise, offers an objective determination of functional capacity and exercise tolerance, and provides information to be used in designing an exercise rehabilitation program in burn injured individuals [42]. As shown by the results of this study, physiological impairments and functional limitations
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following burn need to be considered in the prescription of frequency, intensity, mode and duration of aerobic exercise. Aerobic exercise three times a week for 20–40 min at 70–85% VO2peak over 12 weeks has been reported to improve pulmonary function and exercise tolerance in burn injured children [2]. Promoting participation in physical activity in adults beyond the acute phase of burn could assist in improving long term impairments in pulmonary function and low aerobic capacity that may exist in these patients, potentially enhancing quality of life. Ideally, SpO2 should be monitored to assess the degree of arterial desaturation and the severity of any impairment, which may help to determine the effectiveness of exercise interventions in adults who have sustained a burn. Although prolonged exercise at moderate intensities only very rarely causes EIAH in healthy males [43], significant desaturation during submaximal exercise has been reported in females [44]. Therefore, progressive interval training should be considered in the aerobic exercise prescription of burn injured adults, as this type of exercise includes a recovery component in addition to the training stimulus, which may allow for sufficient recovery of SaO2.
4.
Conclusion
Despite extensive literature detailing structural and functional impairments of the cardiopulmonary system following severe burn injuries, this is one of few studies that have investigated the long term effect of these impairments on exercise tolerance and physical activity participation in these patients. Results from this study demonstrate that compromised pulmonary function may still exist in some individuals, even up to 5 years post injury, which may lead to significant oxygen desaturation during exercise. When compared to a healthy control group, burn injured patients displayed a significantly lower aerobic capacity, and reported significantly less participation in high intensity, leisure-related physical activity. Findings of this research outline specific limitations of the cardiopulmonary system in adults who have sustained a burn, which may need to be considered in the prescription of aerobic exercise to ensure interventions elicit the best possible functional outcome in this patient population.
Conflict of interest statement All authors concur that there are no financial or personal relationships with other people or organisations that may inappropriately influence the content of the work submitted for publication.
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