Original Article Ann Rehabil Med 2017;41(4):659-666 pISSN: 2234-0645 • eISSN: 2234-0653 https://doi.org/10.5535/arm.2017.41.4.659
Annals of Rehabilitation Medicine
Respiratory Muscle Strength in Patients With Chronic Obstructive Pulmonary Disease Nam-Sik Kim, MD1, Jeong-Hwan Seo, MD, PhD1, Myoung-Hwan Ko, MD, PhD1, Sung-Hee Park, MD, PhD1, Seong-Woong Kang, MD, PhD2,3, Yu Hui Won, MD, PhD1 1
Department of Physical Medicine and Rehabilitation, Research Institute of Clinical Medicine of Chonbuk National University–Biomedical Research Institute of Chonbuk National University Hospital, Jeonju; 2 Department of Rehabilitation Medicine and Rehabilitation Institute of Neuromuscular Disease, Yonsei University College of Medicine, Seoul; 3Pulmonary Rehabilitation Center, Gangnam Severance Hospital, Seoul, Korea
Objective To compare the respiratory muscle strength between patients with stable and acutely exacerbated (AE) chronic obstructive pulmonary disease (COPD) at various stages. Methods A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. Patients were subdivided into COPD stages 1–4 according to the Global Initiative for Chronic Obstructive Lung Disease guidelines: mild, moderate, severe, and very severe. A rehabilitation physician reviewed their medical records and initial assessment, including spirometry, maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), COPD Assessment Test, and modified Medical Research Council scale. We then compared the initial parameters in patients with a stable condition and those at AE status. Results The AE group (n=94) had significantly lower MIP (AE, 55.93±20.57; stable, 67.88±24.96; p=0.006) and MIP% (AE, 82.82±27.92; stable, 96.64±30.46; p=0.015) than the stable patient group (n=36). MIP, but not MEP, was proportional to disease severity in patients with AE and stable COPD. Conclusion The strength of the inspiratory muscles may better reflect severity of disease when compared to that of expiratory muscles. Keywords Chronic obstructive pulmonary disease, Respiratory muscles, Rehabilitation, Muscle strength, Dyspnea
INTRODUCTION Chronic obstructive pulmonary disease (COPD) is one of the most common chronic lung diseases, characterized
by airway limitation or obstruction. It is a progressive and partially reversible respiratory disorder which shows a particular chronic inflammatory response caused by toxins or gas inhalation [1-3]. One of the most charac-
Received August 3, 2016; Accepted December 5, 2016 Corresponding author: Yu Hui Won Department of Physical Medicine and Rehabilitation, Chonbuk National University Hospital, 20 Geonji-ro, Deokjin-gu, Jeonju 54907, Korea. Tel: +8263-250-2781, Fax: +82-63-254-4145, E-mail: [email protected] ORCID: Nam-Sik Kim (http://orcid.org/0000-0003-0731-729X); Jeong-Hwan Seo (http://orcid.org/0000-0002-6915-6674); Myoung-Hwan Ko (http:// orcid.org/0000-0002-0566-3677); Sung-Hee Park (http://orcid.org/0000-0002-4743-2551); Seong-Woong Kang (http://orcid.org/0000-0002-72793893); Yu Hui Won (http://orcid.org/0000-0003-2007-9652). This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright © 2017 by Korean Academy of Rehabilitation Medicine
Nam-Sik Kim, et al. teristic symptoms of COPD is dyspnea and many factors are known to be involved in its mechanism, including airflow limitation, gas trapping, gas exchange abnormalities, mucus hypersecretion, respiratory muscle dysfunction, and skeletal muscle dysfunction [4-6]. Among these, skeletal muscle dysfunction is characterized by reduced muscle mass, reduced strength and endurance, atrophy of type I and IIa muscle fibers, and decreased oxidative enzyme capacity [7,8]. In terms of skeletal muscle dysfunctions, the quadriceps muscle has been primarily studied. Patients with COPD demonstrated increased ventilatory stress even with the same amount of exercise due to the accumulation of carbon dioxide and increases in lactic acid [9,10]. Respiratory muscles are also skeletal muscles, and respiratory muscle dysfunction in patients with COPD may be caused by hyperinflation of the lung or diaphragm flattening and shortening. As a result of respiratory muscle dysfunction, reduced inspiratory muscle strength and endurance increased the risk of hypercapnic respiratory failure, limited exercise, and acute exacerbation (AE), despite diaphragm adaptation [11,12]. Pulmonary rehabilitation (PR) in patients with COPD mitigates symptoms, increases exercise capacities and enhances psychological stability, ultimately contributing to the prevention of complications caused by respiratory failure [13-16]. Most rehabilitation guidelines recommended aerobic and muscle strengthening exercises for the arms and legs as the basic PR program. Currently, inspiratory muscle training (IMT) as part of respiratory muscle rehabilitation is recommended only for patients with inspiratory muscle weakness [1,3]. However, some reports suggest that respiratory muscle trainings, such as IMT in patients with respiratory muscle weakness, might improve dyspnea and subsequently the patient’s quality of life [17-19]. IMT has been suggested for patients with inspiratory muscle weakness at the start of PR [3], but an adequate guideline has not yet been established to assess the minimal inspiratory muscle weakness level that requires IMT. In addition, specific data regarding the severity of inspiratory muscles in patients with COPD is lacking. To the best of our knowledge, a prior study classified maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) according to COPD stage (mild, moderate, and severe) to show declines in MIP and MEP, and according to COPD severity in comparison with those in the control group [20]. As of yet, MIP% and
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MEP%, as well as comparisons of severity-specific respiratory muscle strength between patients with stable and AE COPD have not been reported. The present study aims to determine whether respiratory muscle strength (including inspiratory and expiratory muscles) decreases according to COPD stage, and whether such differences in respiratory muscle strength vary between patients with a stable condition and those at AE status.
MATERIALS AND METHODS Subjects A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. The inclusion criteria were patients diagnosed with COPD with a forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) of less than 70% in spirometry evaluation. The patients were consulted as inpatients or registered as outpatients at the Pulmonary Rehabilitation Center of Chonbuk National University Hospital, between March 2014 and May 2016. The severity of COPD was classified based on FEV1 predictions as follows: stage I (FEV1≥80%), stage II (50%≤FEV1
Annals of Rehabilitation Medicine
Respiratory Muscle Strength in Patients With Chronic Obstructive Pulmonary Disease Nam-Sik Kim, MD1, Jeong-Hwan Seo, MD, PhD1, Myoung-Hwan Ko, MD, PhD1, Sung-Hee Park, MD, PhD1, Seong-Woong Kang, MD, PhD2,3, Yu Hui Won, MD, PhD1 1
Department of Physical Medicine and Rehabilitation, Research Institute of Clinical Medicine of Chonbuk National University–Biomedical Research Institute of Chonbuk National University Hospital, Jeonju; 2 Department of Rehabilitation Medicine and Rehabilitation Institute of Neuromuscular Disease, Yonsei University College of Medicine, Seoul; 3Pulmonary Rehabilitation Center, Gangnam Severance Hospital, Seoul, Korea
Objective To compare the respiratory muscle strength between patients with stable and acutely exacerbated (AE) chronic obstructive pulmonary disease (COPD) at various stages. Methods A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. Patients were subdivided into COPD stages 1–4 according to the Global Initiative for Chronic Obstructive Lung Disease guidelines: mild, moderate, severe, and very severe. A rehabilitation physician reviewed their medical records and initial assessment, including spirometry, maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), COPD Assessment Test, and modified Medical Research Council scale. We then compared the initial parameters in patients with a stable condition and those at AE status. Results The AE group (n=94) had significantly lower MIP (AE, 55.93±20.57; stable, 67.88±24.96; p=0.006) and MIP% (AE, 82.82±27.92; stable, 96.64±30.46; p=0.015) than the stable patient group (n=36). MIP, but not MEP, was proportional to disease severity in patients with AE and stable COPD. Conclusion The strength of the inspiratory muscles may better reflect severity of disease when compared to that of expiratory muscles. Keywords Chronic obstructive pulmonary disease, Respiratory muscles, Rehabilitation, Muscle strength, Dyspnea
INTRODUCTION Chronic obstructive pulmonary disease (COPD) is one of the most common chronic lung diseases, characterized
by airway limitation or obstruction. It is a progressive and partially reversible respiratory disorder which shows a particular chronic inflammatory response caused by toxins or gas inhalation [1-3]. One of the most charac-
Received August 3, 2016; Accepted December 5, 2016 Corresponding author: Yu Hui Won Department of Physical Medicine and Rehabilitation, Chonbuk National University Hospital, 20 Geonji-ro, Deokjin-gu, Jeonju 54907, Korea. Tel: +8263-250-2781, Fax: +82-63-254-4145, E-mail: [email protected] ORCID: Nam-Sik Kim (http://orcid.org/0000-0003-0731-729X); Jeong-Hwan Seo (http://orcid.org/0000-0002-6915-6674); Myoung-Hwan Ko (http:// orcid.org/0000-0002-0566-3677); Sung-Hee Park (http://orcid.org/0000-0002-4743-2551); Seong-Woong Kang (http://orcid.org/0000-0002-72793893); Yu Hui Won (http://orcid.org/0000-0003-2007-9652). This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright © 2017 by Korean Academy of Rehabilitation Medicine
Nam-Sik Kim, et al. teristic symptoms of COPD is dyspnea and many factors are known to be involved in its mechanism, including airflow limitation, gas trapping, gas exchange abnormalities, mucus hypersecretion, respiratory muscle dysfunction, and skeletal muscle dysfunction [4-6]. Among these, skeletal muscle dysfunction is characterized by reduced muscle mass, reduced strength and endurance, atrophy of type I and IIa muscle fibers, and decreased oxidative enzyme capacity [7,8]. In terms of skeletal muscle dysfunctions, the quadriceps muscle has been primarily studied. Patients with COPD demonstrated increased ventilatory stress even with the same amount of exercise due to the accumulation of carbon dioxide and increases in lactic acid [9,10]. Respiratory muscles are also skeletal muscles, and respiratory muscle dysfunction in patients with COPD may be caused by hyperinflation of the lung or diaphragm flattening and shortening. As a result of respiratory muscle dysfunction, reduced inspiratory muscle strength and endurance increased the risk of hypercapnic respiratory failure, limited exercise, and acute exacerbation (AE), despite diaphragm adaptation [11,12]. Pulmonary rehabilitation (PR) in patients with COPD mitigates symptoms, increases exercise capacities and enhances psychological stability, ultimately contributing to the prevention of complications caused by respiratory failure [13-16]. Most rehabilitation guidelines recommended aerobic and muscle strengthening exercises for the arms and legs as the basic PR program. Currently, inspiratory muscle training (IMT) as part of respiratory muscle rehabilitation is recommended only for patients with inspiratory muscle weakness [1,3]. However, some reports suggest that respiratory muscle trainings, such as IMT in patients with respiratory muscle weakness, might improve dyspnea and subsequently the patient’s quality of life [17-19]. IMT has been suggested for patients with inspiratory muscle weakness at the start of PR [3], but an adequate guideline has not yet been established to assess the minimal inspiratory muscle weakness level that requires IMT. In addition, specific data regarding the severity of inspiratory muscles in patients with COPD is lacking. To the best of our knowledge, a prior study classified maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) according to COPD stage (mild, moderate, and severe) to show declines in MIP and MEP, and according to COPD severity in comparison with those in the control group [20]. As of yet, MIP% and
660
www.e-arm.org
MEP%, as well as comparisons of severity-specific respiratory muscle strength between patients with stable and AE COPD have not been reported. The present study aims to determine whether respiratory muscle strength (including inspiratory and expiratory muscles) decreases according to COPD stage, and whether such differences in respiratory muscle strength vary between patients with a stable condition and those at AE status.
MATERIALS AND METHODS Subjects A retrospective medical record review was conducted on patients with COPD from March 2014 to May 2016. The inclusion criteria were patients diagnosed with COPD with a forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) of less than 70% in spirometry evaluation. The patients were consulted as inpatients or registered as outpatients at the Pulmonary Rehabilitation Center of Chonbuk National University Hospital, between March 2014 and May 2016. The severity of COPD was classified based on FEV1 predictions as follows: stage I (FEV1≥80%), stage II (50%≤FEV1
