Abstract
The pillars of comprehensive pulmonary rehabilitation program for chronic obstructive pulmonary disease (COPD) patients include physical exercise and good nutrition. The aim of this study was to evaluate the efficacy of pulmonary rehabilitation, which included physical exercise and chicken egg white supplementation, on the quality of life (QoL) and functional capacity among patients with stable COPD. The COPD patients were enrolled prospectively in this quasi-experimental study and completed a 12-week smartphone-guided home-based physical exercise program that comprised strength and resistance training three times per week for 30 minutes each session. Participants were divided into two groups: the control group who underwent physical exercise only, and the intervention group who had physical exercise and chicken egg white supplementation as a protein source. Patient characteristics including sex, age, nutritional status, comorbidities, smoking status, and obstruction severity, were evaluated. The COPD assessment test (CAT) score and six-minute walk test (6MWT) were used as the parameters to evaluate QoL and functional capacity, respectively. Of the total 50 patients included in the study, 12 were excluded due to follow-up and adherence problems. Our data indicated there were significant CAT score reduction and 6MWT improvement in both control and intervention groups after 12 weeks compared to baseline data. However, reduction of mean CAT score was higher in intervention compared to control group (-13.47±6.49 vs -5.42±5.07, p<0.001). In addition, the improvement of 6MWT was also higher in intervention group compared to control group (145.47±69.2 vs 32.42±17.3 meters, p<0.001). In conclusion, chicken egg white supplement to male patients with stable COPD who exercise with resistance and strength training could improve the QoL and functional capacity.
Keywords: COPD, physical exercise, chicken egg white, 6MWT, CAT score
Introduction
Patients with chronic obstructive pulmonary disease (COPD), the majority of whom are elderly, experience a negative cycle of physical inactivity, decreasing muscle mass, and increasing shortness of breath. The key element required to stop the cycle is a comprehensive pulmonary rehabilitation program. Exercise has been shown to be beneficial in all stages of COPD as part of pulmonary rehabilitation programs, improving exercise tolerance, muscular strength, quality of life (QoL), and lowering levels of exhaustion and shortness of breath [1-3].
Despite the benefits, the number of COPD patients who carry out pulmonary rehabilitation programs routinely is very low due to various problems, including the inability to carry out physical activity due to muscle weakness, shortness of breath, transportation problems, schedule discrepancies, and difficulty accessing the pulmonary rehabilitation center [4-7]. Currently, exercise programs for COPD patients conducted outside of medical institutions, such as gyms, private homes, and online, may represent a new approach that will draw in more patients and ensure that these programs are implemented for a longer period of time and are more satisfactory. Several studies have been done to evaluate the efficacy of pulmonary rehabilitation programs run outside of medical facilities [4-7]. This program was specifically created for each patient based on their own requirements. Furthermore, it is anticipated that the use of smartphone applications will facilitate and make it simpler for COPD patients to engage in physical exercise whenever they decide, in accordance with their level of comfort and time availability, in order to increase their participation and further maximize the advantages of physical exercise on functional capacity [3-9].
Providing protein supplements to elderly, particularly COPD patients, has been linked to weight gain, improved muscular function, lower risk of hospitalization and mortality, and higher nutritional status [10-12]. Protein supplementation significantly increased muscle mass and exercise capacity [13]. The aim of this study was to simultaneously assess the effect of independent smartphone-guided physical exercise along with the effect of adding chicken egg white in stable COPD patients.
Methods
Study setting
A quasi-experimental study was conducted among COPD patients throughout January 2021 to December 2022 at Prof. dr. Chairuddin Panusunan Lubis Universitas Sumatera Utara Hospital and Siti Hajar Hospital, Medan, Indonesia. After selected, the study participants, who were divided into control and intervention groups, completed the COPD assessment test (CAT) questionnaire and the six-minute walk test (6MWT) as baseline data. The control group performed independent physical exercise three times per week for a length of 30 minutes over a 12-week period utilizing the "PARU SEHAT" application guidance on an Android smartphone. In addition to participating in physical exercise, the intervention group consumed egg white supplementation of 10 eggs/exercise. After 12 weeks of study, CAT score and 6MWT were reassessed to determine the QoL and functional capacity, respectively.
Patient selection and criteria
Using a non-probability sampling technique with consecutive sampling, COPD patients who were diagnosed according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD)/Indonesian Society of Respirology (ISR) were recruited from the outpatient respiratory clinic at Prof. dr. Chairuddin Panusunan Lubis Universitas Sumatera Utara Hospital and Siti Hajar Hospital, Medan, Indonesia. All subjects who arrived sequentially and met the eligibility requirements were included in the study.
The inclusion criteria in this study were: (a) age range of 40 to 80 years old; (b) receiving appropriate therapy provided by outpatient clinic based on COPD groups; (c) absence of malignancy, severe cardiovascular disease such as acute coronary syndrome or acute chronic heart failure, neuromusculoskeletal disorders such as stroke, severe osteoarthritis, or other illnesses that affect the movement, renal diseases, impaired cognitive; (d) not having a history of egg allergy; and (e) able to utilize Android smartphone application. Patients who did not implement the intervention as advised, experienced interference preventing subjects from performing the intervention, passed away during the study, or withdrew from participation were excluded from the study. All patients provided their informed consent before participating in this study.
Procedure and variables
The patients were divided into two groups: the control group performed physical exercise only, and the intervention group did physical exercise and provided with chicken egg white supplementation. At the time of admission, the patient characteristics including sex, age, nutritional status based on body mass index (BMI), and comorbidities were collected. Smoking status was calculated by multiplying years of smoking by the daily cigarette consumption (Brinkmann index) and obstruction severity was classified according to Global Initiative for Chronic Obstructive Lung Disease (GOLD). The endpoints (functional capacity and quality of life (QoL)) were measured at the time of admission and at the end of the study.
Interventions
Physical exercise included strength and resistance training guided by Android smartphone application “PARU SEHAT”. Physical exercise adopted in this study were adjusted to patients’ individual capabilities based on recommendations for resistance (Table 1) and strength trainings (Table 2).
Table 1. Endurance training recommendation adopted in the study.
| Component | Continuous endurance training | Interval resistance training |
|---|---|---|
| Frequency Mode | 3-4 days/week Continuous | 3-4 days/week Interval mode: 30 seconds of exercise, 30 seconds of rest, or 20 seconds of exercise, 40 seconds of rest |
| Intensity | Initially 60-70% of peak work rate Increase workload by 5-10% as tolerated Progressively tried up to 80-90% of baseline peak work rate | Initially 80-100% of peak work rate for the first three to four sessions Increase workload by 5-10% as tolerated Gradually try to reach 150% of baseline peak work rate |
| Duration | Initially 10-15 minutes for the first three to four sessions Progressively increase the duration of the exercise to 30-40 minutes | Initially 15-20 minutes for the first three to four sessions Progressively increase exercise duration to 45-60 minutes (including rest time) |
| Borg scale Breathing techniques | 4-6 Recommend pursed lip breathing or use of a positive expiratory pressure device to prevent dynamic hyperinflation and to reduce respiratory rate | 4-6 Recommend pursed lip breathing or use of a PEP device to prevent dynamic hyperinflation and to reduce respiratory rate |
Adapted from Ambrosino and Strambi [14].
Table 2. Strength training recommendation adopted in the study.
| Component | Description |
|---|---|
| Frequency Objective | 2-3 days/week Targets fatigue in muscle groups, especially the upper and lower extremities through a certain number of repetitions of movements |
| Mode Intensity | Two to four sets of 6 to 12 repetitions while lifting load of 0.5 kg in both hands 50-85% of 1RM (one repetition maximum) as a reference point Increase workload by 2-10% if one or two repetitions above the desired number is still possible on two consecutive training sessions |
| Tempo | Medium (1-2 seconds concentric and 1-2 seconds eccentric) |
Adapted from Nici et al. [15].
Using the conversion of daily protein requirement for people over the age of 40, 30 grams of chicken egg white supplementation, up to 10 eggs per day, was provided. Physical exercise was practiced three times per week for a minimum of 30 minutes per day for 12 weeks. The consumption of chicken egg whites was done on the same day as the exercise day. By requesting the patients to provide videos of themselves exercising, consuming chicken egg whites, and filling out a timetable for their physical exercise, an evaluation of the intervention's implementation was carried out on a daily basis.
Endpoints
The endpoints evaluated in this study were functional capacity and QoL. Six-minute walk test (6MWT), conducted in accordance with American Thoracic Society (ATS) recommendations, was used to evaluate functional capacity while COPD assessment test (CAT) score was used to evaluate QoL. At the time of admission and at the end of the study, the CAT score and 6MWT were evaluated. The CAT scales from 0 to 40. A higher score denotes a more serious disease impact.
Statistical analyses
All variables were calculated for the arithmetic mean, percentage, and standard deviation (SD). Fisher's Exact test was used to examine the homogeneity between group. The Shapiro-Wilk test was used to determine normality and revealed the data were distributed normally. The independent Student t-test was used to assess the association between intervention and outcomes. A two-tailed p<0.05 was considered to be statistically significant.
Results
Subject characteristics
Throughout the course of the study, 50 patients were enrolled. However, 12 participants discontinued the study due to follow-up and adherence problems. This made a total of 38 patients with stable COPD were involved with a mean age of 66.97±6.25 years (range 54–80 years) (Table 3). All of the patients were male. The majority of the control and intervention groups were >60 years old (84.2% and 89.5%, respectively); 68.4% and 94.7% had a smoking history with a severe Brinkman index, respectively. Overall, there was no difference in characteristics between the control and intervention groups (Table 3).
Table 3. Characteristics of stable chronic obstructive pulmonary disease (COPD) patients included in this study.
| Characteristics | Control group | Intervention group | Total | p-value | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (n=19) | (n=19) | n (%) | |||||||||
| n (%) | n (%) | ||||||||||
| Sex | |||||||||||
| Male | 19 (100.0) | 19 (100.0) | 38 (100.0) | 1.00 | |||||||
| Female | 0 (0.0) | 0 (0.0) | 0 (0.0) | ||||||||
| Age (years) | |||||||||||
| 51-60 | 3 (15.8) | 2 (10.5) | 5 (13.1) | 0.62 | |||||||
| 61-70 | 8 (42.1) | 13 (68.4) | 21 (55.2) | ||||||||
| 71-80 | 8 (42.1) | 4 (21.1) | 12 (31.5) | ||||||||
| Nutritional status (BMI, kg/m2) | |||||||||||
| Underweight (<18.5) | 2 (5.3) | 2 (5.3) | 4 (10.5) | 0.45 | |||||||
| Normal (18.5-24.9) | 7 (18.4) | 8 (21.1) | 15 (39.5) | ||||||||
| Overweight (25.0-29.9) | 2 (5.3) | 5 (13.2) | 7 (18.4) | ||||||||
| Obese (>30) | 8 (21.1) | 4 (10.5) | 12 (31.6) | ||||||||
| Comorbidity | |||||||||||
| None | 3 (13.6) | 5 (22.7) | 8 (18.1) | 0.43 | |||||||
| Hypertension | 13 (59.1) | 7 (31.8) | 20 (45.5) | ||||||||
| Pulmonary tuberculosis | 4 (18.2) | 6 (27.3) | 10 (22.7) | ||||||||
| Type 2 diabetes mellitus | 1 (4.5) | 2 (9.1) | 3 (6.8) | ||||||||
| Hepatitis C | 1 (4.5) | 0 (0) | 1 (2.3) | ||||||||
| Hyperuricemia | 0 (0.0) | 1 (4.5) | 1 (2.3) | ||||||||
| Congestive heart failure | 0 (0.0) | 1 (4.5) | 1 (2.3) | ||||||||
| Smoking status (Brinkman Index) | |||||||||||
| Mild (1-199) | 2 (10.5) | 0 (0.0) | 2 (5.3) | 0.10 | |||||||
| Moderate (200-599) | 4 (21.1) | 1 (5.3) | 5 (13.2) | ||||||||
| Severe (>600) | 13 (68.4) | 18 (94.7) | 31 (81.6) | ||||||||
| Obstruction severity | |||||||||||
| GOLD 1 (mild) | 0 (0.0) | 0 (0.0) | 0 (0.0) | 0.07 | |||||||
| GOLD 2 (moderate) | 12 (63.2) | 5 (26.3) | 17 (44.7) | ||||||||
| GOLD 3 (severe) | 4 (21.1) | 6 (31.6) | 10 (26.3) | ||||||||
| GOLD 4 (very severe) | 3 (15.8) | 8 (42.1) | 11 (28.9) | ||||||||
GOLD: Global Initiative for Chronic Obstructive Lung Disease
COPD assessment test (CAT) score
At the time of admission, the mean CAT scores of control and intervention groups were 16.21±6.27 and 20.32±8.79, respectively (Table 4). After 12 weeks of intervention, the mean CAT scores of control and intervention groups decreased to 10.79±3.71 (p=0.003) and 6.84±3.61 (p=0.020), respectively which shown significant improvement compared to baseline data in both groups (Table 4 and Figure 1A). The mean decrease of CAT scores for control group was 5.42±5.07 and 13.47±6.49 for intervention group (Table 4 and Figure 2A). Analysis of CAT score reduction indicating there was a significant change between control and intervention groups, p<0.001 (Table 4).
Table 4. Comparison of COPD assessment test (CAT) score and six-minute walk test (6MWT) between study groups.
| Outcome | Control group | Intervention group | p-value b | ||
|---|---|---|---|---|---|
| Pre | Post | Pre | Post | ||
| CAT score | |||||
| Mean (±SD) | 16.21±6.27 | 10.79±3.71 | 20.32±8.79 | 6.84±3.61 | <0.001 |
| Mean change (±SD) | -5.42±5.07 | -13.47±6.49 | |||
| p-value a | 0.003 | 0.020 | |||
| 6MWT (meters) | |||||
| Mean (±SD) | 276±85.14 | 308.4±82.66 | 223.8±82.67 | 369.3±99.01 | <0.001 |
| Mean change (±SD) | 32.42±17.26 | 145.47±69.17 | |||
| p-value a | <0.001 | <0.001 | |||
Comparison between mean pre and post within control group or intervention group
Comparison between mean change of two groups (control and intervention groups)
Figure 1. Improvement of COPD assessment test (CAT) score (A) and six-minute walk test (6MWT) (B) among stable COPD patients following physical exercise only or combination with chicken egg white supplementation.
Figure 2. Changes of COPD assessment test (CAT) score (A) and six-minute walk test (6MWT) (B) between control group (physical exercise only) and intervention group (combination of physical exercise and chicken egg white supplementation).
Six-minute walk test (6MWT)
The baseline mean of 6MWT for control and intervention groups was 276±85.1 and 223.8±82.7 meters, respectively (Table 4). Compared to the baseline data, the mean 6MWT for control and intervention groups increased significantly to 308.4±82.7 meters (p<0.001) and 369.3±99 meters (p<0.001), respectively, after 12 weeks (Table 4 and Figure 1B). Participants in intervention group experienced a higher average rise of 6MWT (145.47±69.2 meters) compared to control group (32.42±17.3) (Table 4 and Figure 2B). Our data indicated that the 6MWT improvement was significantly higher in intervention group compared to control group (p<0.001) (Table 4).
Discussion
Our data indicate that there was an improvement in QoL and functional capacity in COPD patients who engaged in resistance and strength training and consumed chicken egg whites. Patients who completed physical exercise alone shown substantial benefits, and the benefits increased when physical exercise was combined with diet changes that included chicken egg whites. These suggest that chicken egg whites as protein supplements along with physical exercise promote protein anabolism as contrasted to catabolism and preserve muscle physiology and morphology. The CAT scores of control and intervention groups differed significantly. Compared to the control group, who engaged only in physical exercise, CAT score of the intervention group, who received chicken egg white supplementation, was lower. A CAT score reduction of 2 points is considered a minimum clinically important difference (MCID) in individuals with COPD [16]. Hence, supplementing with chicken egg whites can enhance the QoL for COPD patients who exercise.
A comprehensive pulmonary rehabilitation program must include physical exercise as the main element. Physical exercise has shown to be useful at all stages of COPD. This improves exercise tolerance, muscular strength, QoL, and lowering levels of fatigue and shortness of breath [1-3]. There was a substantial improvement in exercise capacity, functional capacity, and QoL in 40 COPD patients who were randomized to the intervention of resistance and strength training three times per week for 12 weeks [17]. This is consistent with the findings of this research.
Apart from physical exercise, diet plays a significant role in pulmonary rehabilitation. With aging, muscle depletion is made worse by COPD, which is frequently accompanied by a rise in the rate of protein breakdown and a reduction in the rate of protein synthesis [18]. In accordance with the results of this present study, other studies have demonstrated that supplying nutrition, particularly protein, can significantly enhance functional capacity and QoL while also lowering morbidity and mortality in COPD patients [10,19]. Khan et al. found a significant improvement in the 6MWT and QoL after consuming a high-protein diet [20]. In COPD patients undergoing pulmonary rehabilitation, high-protein supplementation can reduce clinical symptoms and increase exercise tolerance in a way that is beneficial to and acceptable to the patients [21].
With the help of video guidance, our study participants independently performed physical exercise at home. This shows that, despite the fact that traditionally supervised pulmonary rehabilitation is still the gold standard and first option of treatment, home-based pulmonary rehabilitation is a promising substitution. The degree of shortness of breath in COPD patients can be improved, according to data that is comparable to that found in this study and supports the use of home-based pulmonary rehabilitation programs [7].
Non-compliance and improper physical exercise technique are the challenges in implementing this home-based rehabilitation. This was avoided in this current study by requesting participants to provide recordings of their physical exercise sessions and to report their attendance on a regular basis so that the discipline and precision of their movements could be evaluated. Lethargy, apprehension that shortness of breath would worsen, and physical weakness were common reasons why patients refrained from participation. Healthcare professionals must thus inform patients that physical inactivity genuinely does have negative impacts: it increases morbidity, increases the likelihood of exacerbations, and diminishes QoL [22]. The physical exercise used in this study were relatively simple and performed in a sitting position, allowing COPD patients to tolerate even the most severe degrees of obstruction (GOLD 4).
Eggs are an inexpensive, easy-to-find, and easily digestible source of high-quality protein. The most predominant protein in plasma is albumin, which is found in egg white. Albumin helps to regulate blood osmotic pressure, transports numerous compounds through the circulation, and lowers blood acidity. All of the necessary amino acids that the body requires are present in egg white, which also provides a number of health benefits like boosting the immune system and cell development [23-25]. Egg white comprises 11–12% protein, with ovalbumin, which is regarded as the egg white's primary protein, making up the majority (54%), followed by conalbumin (12%), ovomucoid (11%), lysozyme (3.5%), and ovomucin (3.5%) [26]. Consequently, egg whites are a good source of protein for those who require high amounts of protein, such as elderly COPD patients. The protein found in egg whites is also affordable, accessible, and free of cholesterol. Consuming protein sources from egg whites can improve QoL and functional capacity in COPD patients. Given that COPD is a chronic, progressive, and irreversible disease dietary supplementation with chicken egg white are essential. Our data indicated that combination of home-based exercise under supervision and chicken egg white supplementation was effective to improve the QoL of COPD patients,
There are some limitations of this study. Besides the limited number of study participants, it cannot be conclusively said that the treatments were advantageous for female COPD patients since all study participants were men due to the small number of women with COPD at the study location. Therefore, further study that takes into account more COPD patients is required.
Conclusion
Implementation of independent physical exercise guided by Android smartphone application could improve the QoL and functional capacity of stable COPD patients. In addition, combination of chicken egg white supplementation with physical exercise exhibits even greater advantages. Therefore, besides pharmacological management, non-pharmacological therapy for stable COPD patients in outpatient clinics in the form of implementing independent smartphone-guided physical exercise accompanied by supplementation of chicken egg white diet is strongly recommended, especially for male patients.
Acknowledgments
We acknowledge all of the individuals who took part in the study as well as the staff members at Prof. dr. Chairuddin Panusunan Lubis Universitas Sumatera Utara Hospital and Siti Hajar Hospital in Medan for recruiting the study participants and monitoring the exercise schedule.
Ethics approval
The Universitas Sumatera Utara Health Research Ethics Committee approved this study with the approval number 503/KEPK/USU/2022.
Competing interests
All the authors declare that there are no conflicts of interest.
Funding
This study was financially supported by Directorate of Research and Community Service (DRPM) Ministry of Education, Culture, Research, and Technology Republic of Indonesia.
Underlying data
Derived data supporting the findings of this study are available from the corresponding author on request.
How to cite
Sihombing B, Tarigan AP, Pandia P, et al. Functional capacity and quality of life improvement in stable chronic obstructive pulmonary disease (COPD) patients following physical exercise and chicken egg white supplementation. Narra J 2023; 3 (3): e404 - http://doi.org/10.52225/narra.v3i3.404.
References
- 1.Spruit MA, Burtin C, De Boever P, et al. COPD and exercise: Does it make a difference? Breathe 2016;12(2):e38–e49. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Gloeckl R, Marinov B, Pitta F.. Practical recommendations for exercise training in patients with COPD. Eur Respir Rev 2013;22(128):178–186. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Alkan H, Sarsan A, Topuz O, et al. Effectiveness of home rehabilitation programme in chronic obstructive pulmonary disease. Turk J Phys Med Rehab 2006;52(2):51–54. [Google Scholar]
- 4.Mitchell KE, Johnson-Warrington V, Apps LD, et al. A self-management programme for COPD: A randomised controlled trial. Eur Respir J 2014;44(6):1538–1547. [DOI] [PubMed] [Google Scholar]
- 5.Bourbeau J. Making pulmonary rehabilitation a success in COPD. Swiss Med Wkly 2010;140:w13067. [DOI] [PubMed] [Google Scholar]
- 6.Hansen H, Bieler T, Beyer N, et al. Supervised pulmonary tele-rehabilitation versus pulmonary rehabilitation in severe COPD: A randomised multicentre trial. Thorax 2020;75(5):413–421. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Horton EJ, Mitchell KE, Johnson-Warrington V, et al. Comparison of a structured home-based rehabilitation programme with conventional supervised pulmonary rehabilitation: A randomised non-inferiority trial. Thorax 2018;73(1):29–36. [DOI] [PubMed] [Google Scholar]
- 8.Holland AE, Mahal A, Hill CJ, et al. Home-based rehabilitation for COPD using minimal resources: A randomised, controlled equivalence trial. Thorax 2017;72(1):57–65. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Rassouli F, Boutellier D, Duss J, et al. Digitalizing multidisciplinary pulmonary rehabilitation in COPD with a smartphone application: An international observational pilot study. Int J Chron Obstruct Pulmon Dis 2018;13:3831–3836. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Chapman I, Oberoi A, Giezenaar C, et al. Rational use of protein supplements in the elderly—relevance of gastrointestinal mechanisms. Nutrients 2021;13(4):1227. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Tieland M, Borgonjen-Van Den Berg KJ, Van Loon LJC, et al. Dietary protein intake in dutch elderly people: A focus on protein sources. Nutrients 2015;7(12):9697–9706. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Baum JI, Kim IY, Wolfe RR. Protein consumption and the elderly: What is the optimal level of intake? Nutrients 2016;8(6):359. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Park Y, Choi JE, Hwang HS. Protein supplementation improves muscle mass and physical performance in undernourished prefrail and frail elderly subjects: A randomized, double-blind, placebo-controlled trial. Am J Clin Nutr 2018;108(5):1026–1033. [DOI] [PubMed] [Google Scholar]
- 14.Ambrosino N, Strambi S.. New strategies to improve exercise tolerance in chronic obstructive pulmonary disease. Eur Respir J 2004;24(2):313–322. [DOI] [PubMed] [Google Scholar]
- 15.Nici L, ZuWallack R, Wouters E, et al. On pulmonary rehabilitation and the flight of the bumblebee: The ATS/ERS statement on pulmonary rehabilitation. Eur Respir J 2006;28(3):461–462. [DOI] [PubMed] [Google Scholar]
- 16.Kon SSC, Canavan JL, Jones SE, et al. Minimum clinically important difference for the COPD Assessment Test: a prospective analysis. Lancet Respir Med 2014;2(3):195–203. [DOI] [PubMed] [Google Scholar]
- 17.Probst VS, Kovelis D, Hernandes NA, et al. Effects of 2 exercise training programs on physical activity in daily life in patients with COPD. Respir Care 2011;56(11):1799–1807. [DOI] [PubMed] [Google Scholar]
- 18.Nguyen HT, Collins PF, Pavey TG, et al. Nutritional status, dietary intake, and health-related quality of life in outpatients with COPD. Int J Chron Obstruct Pulmon Dis 2019;14:215–226. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Barnes PJ, Celli BR. Systemic manifestations and comorbidities of COPD. Eur Respir J 2009;33(5):1165–1185. [DOI] [PubMed] [Google Scholar]
- 20.Khan NA, Kumar N, Daga MK. Effect of dietary supplementation on body composition, pulmonary function and health-related quality of life in patients with stable COPD. Tanaffos 2016;15(4):225–235. [PMC free article] [PubMed] [Google Scholar]
- 21.Aldhahir AM, Aldabayan YS, Alqahtani JS, et al. A double-blind randomised controlled trial of protein supplementation to enhance exercise capacity in COPD during pulmonary rehabilitation: a pilot study. ERJ Open Res 2021;7(1):00077–2021 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Albarrati AM, Gale NS, Munnery MM, et al. Daily physical activity and related risk factors in COPD. BMC Pulm Med 2020;20(1):60. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Kim JH, Song H, Kim HW, et al. Effects of egg white consumption on immune modulation in a mouse model of trimellitic anhydride-induced allergy. Korean J Food Sci Anim Resour 2015;35(3):398–405. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Li-Chan ECY, Kim HO. Structure and chemical compositions of eggs. In: Mine Y, editor. Egg bioscience and biotechnology. New Jersey: John Wiley & Sons; 2008. [Google Scholar]
- 25.Ibrahim HR. Insights into the structure-function relationships of ovalbumin, ovotransferrin, and lysozyme. In: Hen Eggs: Basic and applied science. New York: CRC Press Taylor & Francis; 2000. [Google Scholar]
- 26.Stadelman WJ, Cotterill OJ. Egg science and technology. Fourth Edition. New York: The Haworth Press; 2017. [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Derived data supporting the findings of this study are available from the corresponding author on request.