Introduction

Chronic Obstructive Pulmonary Disease (COPD), a globally pervasive respiratory disease remains the cause of attributable deaths at a rate of 41.9 per 100,000. Over the past three decades, the overall prevalence has increased by 5.9% with a small difference between genders.1 Factors like smoking, second-hand smoke exposure, genetic, predisposition, and developmental, and social influences contribute to the progression of COPD to an irreversible stage. Diagnosis relies on identified risk factors, symptoms such as cough and sputum, and spirometry results indicating persistent airflow obstruction.2 Guidelines for COPD management underscore preventive measures (eg, vaccinations, smoking cessation, and avoidance of exposures) and the treatment manageable traits, including dyspnea, exacerbations, and comorbidities, like sarcopenia, osteoporosis, and others.3,4

Sarcopenia, a frequently discussed concurrent condition with COPD, manifests as a gradual and widespread decline in skeletal muscle in the elderly population, encompassing reduced muscle strength and mass, as well as muscle quality.5 Introduced into consensus definitions in 2010 and recognized as an independent disease in 2016, sarcopenia lacks a singular diagnostic criterion despite widely acknowledged definitions by the European Working Group on Sarcopenia in Older People 2 (EWGSOP2) and the Asian Working Group for Sarcopenia 2019 (AWGS2019).6,7 A recent meta-analysis revealed varying sarcopenia the prevalence (10–27%) due to diverse classifications and cut-off thresholds in studies.8 Typically diagnosed using dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA), sarcopenia assessment is complemented by computed tomography (CT) for emphysema characterization in COPD. Emerging tools include CT-morphometric measurement for structure-function associations and CT-quantitative analysis of muscle mass and adipose tissue for assessing disease severity and prognosis in COPD with sarcopenia.9,10

The literature on COPD with sarcopenia encompasses comprehensive reviews, system reviews, and meta-analysis covering relevance,11,12 mechanisms,13 prevalence,14,15 diagnosis and treatment,16 and even pathogenesis based Chinese traditional medicine theory.17,18 However, a notable gap exists in a comprehensive scientometric analysis of the existing literature.

In this article, statistical methods and visualization tools such as CiteSpace and VOSviewer are employed to examine current structures and future trends.19,20 An illustrative example is the bibliometric and visual analysis of mesenchymal stem cells (MSCs) and pulmonary fibrosis (PF) research, effectively summarizing the present state of clinical trials in this field.21 Scientometric analysis, previously applied to depressive disorder research, identifies primary areas of investigation and summarizes associated keywords through manual classification.22 Leveraging these methods, we propose future research directions for COPD with sarcopenia by combining current literature and scientometric analysis.

Data and Methods Research Process

The Web of Science (WoS) database is the preeminent resource in bibliometric studies, surpassing general databases in both usage frequency and the abundance of scientific publications, offering a more extensive array of data sources. A search was systematically conducted in the WoS Core Collection database employing specific terms: (TS= (Pulmonary Disease, Chronic Obstructive) OR AB=(Chronic Obstructive Pulmonary Diseases OR Chronic Obstructive Lung Disease OR COPD)) AND (TS=(Sarcopenia) OR AB=(Sarcopenia OR Sarcopenias OR Muscle atrophy OR Sarcopenic OR Muscle attenuation OR Muscle loss OR Muscle depletion)) on 5 October 2023 and time span limited to 2003–2022. Exclusively, articles and reviews published in English were considered, excluding diverse document types, such as early access, book chapters, meeting abstracts, and letters. Figure 1 elucidates the process of scientometric analysis and provides additional pertinent details.

Figure 1 Flow chart illustrating the scientometric analysis process.

Data Analysis

VOSviewer (version 1.6.19) offers three distinct analyses for scientific cooperation networks: network visualization, overlay visualization, and density visualization. The tool played a pivotal role in conducting bibliometric analysis, exploring collaborations among countries/regions and affiliations, author and co-cited author interactions, co-cited references, and keyword co-occurrences. Additionally, it generated maps for network visualization and overlay visualization. To illustrate the dual-map overlay depicting COPD-related journals with sarcopenia and references featuring citation bursts, CiteSpace (version 6.2.R6) was employed. The comprehensive management of data, analytical support, and creation of tables and figures were seamlessly executed using Origin Pro 2022. The table was improved with the inclusion of Impact Factors (IF) for journals and the H-index for countries/regions, enhancing the depth of the scientometric analysis.

Results Annual Publication Quantity

Between 2003 and 2022, an exhaustive search identified a total of 758 studies (comprising 588 articles and 170 reviews) related to COPD with sarcopenia. Analyzing the search results in the WoS, the annual publication output reveals into two indicates periods. The first stage, spanning from 2003 to 2012, exhibits a gradual yet consistent growth, while the second stage, from 2013 to 2022, indicates a more rapid expansion (Figure 2). Sarcopenia’s introduction in 2010 precedes a period before 2013 with fewer than 30 studies per year on the subject. Post 2014, a notable surge in annual publications is evident. However, the impact of COVID-19 appears to have led to a modest decline in publications in 2019 and 2020, resulting in a brief plateau. Despite this, the overall trend indicates a heightened publication rate in recent years.

Figure 2 Annual publication quantity from 2003 to 2022 related to COPD with sarcopenia.

Countries/Regions and Affiliations

The VOSviewer network visualization map illustrates node size corresponding to the number of publications by a country/region or affiliation. For visual analysis, countries/regions with frequencies of at least 3 (n=35) and affiliations with frequencies of at least 7 (n=36) were selected. Subsequently, a cooperation network was established considering publication quantity and connections within each country/region and affiliation (Figure 3A and B). Line thickness connecting nodes indicates the level of cooperation or citation between projects. Authors are distributed across 57 countries/regions and 1,109 affiliations. As shown in Figure 3A and C, the USA leads with over 170 publications (n=173, 22.82%). Netherlands, England, Spain, and China follow, contributing to over 500 publications (66.36% of the total). Notably, close cooperation exists between the USA and Spain, USA and Netherlands, Netherlands and England. These developed countries contribute significantly, potentially due to COPD with sarcopenia being a global challenge, garnering more funding from developed countries. Examining Figure 3B and D, Maastricht University (Netherlands)tops with 45 publications (5.94%), followed by Pompeu Fabra University (Spain), Royal Brompton & Harefield NHS Foundation Trust (England), National Institute of Health Carlos III (Instituto de Salud Carlos III, Spain), and University of Barcelona (Spain). Utilizing H-index and global rank as reliable measures of scientific achievements or influence, it is evident that the USA, Netherlands and Spain exhibit robust scientific prowess in COPD with sarcopenia research.

Figure 3 Cooperation map illustrating the countries/regions and affiliations.

Notes: (A) Network visualization of countries/regions. (B) Number of publications and H-Index scores for countries/regions. (C) Network visualization of affiliations. (D) Number of publications and global affiliations rank.

A substantial portion (44.86%) of total publications pertains to the respiratory system, geriatrics and gerontology (Figure 4). Chronic respiratory diseases, ranking as the third leading cause of death (7.0% of all deaths), r trail behind cardiovascular diseases and neoplasms. Notably, COPD, a major chronic respiratory ailment, significantly contributes to global mortality and disability driven by aging populations and chronic exposure to inhaled particulate matter.1 The nuanced understanding of COPD with sarcopenia involves multidisciplinary approaches encompassing pharmacology, critical care, internal medicine, nutrition, exercise and rehabilitation, facilitating personalized management.16,23 Thus, there is a higher prevalence of physiology-related publications (9.89%), followed by medicine general internal (9.37%) and nutrition dietetics (8.31%). Studies indicate that interventions such as multistrain probiotics or oral protein supplements can enhance muscle strength and physical abilities in COPD patients with sarcopenia.24,25 Notably, sport science and rehabilitation contribute 5.94% to total publications, underscoring their therapeutic potential against COPD with sarcopenia.26,27 Furthermore, various categories, including multidisciplinary science and neuroscience, highlight the intricate associations of COPD with sarcopenia with other diseases emphasizing the necessity for comprehensive treatment strategies.

Figure 4 Category exploration map related to COPD with sarcopenia.

Journals and Co-Cited Journals

The literature on COPD with sarcopenia encompasses 303 academic journals, with Table 1 highlighting the top 10 journals in this domain. International Journal of Chronic Obstructive Pulmonary Disease leads with 32, publications 4.22%, followed by Journal of Applied Physiology (25 publications, 3.30%) and Journal of Cachexia, Sarcopenia and Muscle (24 publications, 3.17%). Notably, among the top 10 journals, 5 are based in the United States, 4 in England, and 1 each in New Zealand and Switzerland. In this list, 7 journals belong to the Q1 section of the JCR quartile. Furthermore, 6 journals boast IF greater than 5, including Journal of Cachexia, Sarcopenia and Muscle (IF=8.9), European Respiratory Journal (IF=24.3), Respiratory Research (IF=5.8), Thorax (IF=10), Chest (IF=9.6), and American Journal of Respiratory and Critical Care Medicine (IF=24.7). Despite International Journal of Chronic Obstructive Pulmonary Disease having the lowest impact factor among the top 10 (IF=2.8), it has significantly contributed to the field. Interestingly, numerous publications related to COPD with sarcopenia are published in journals with lower impact factors, indicating a focus on sarcopenia as a comorbidity of respiratory diseases in general. This suggests a demand for further research in this interdisciplinary field.

Table 1 Top 10 Journals Related to COPD with Sarcopenia

Based on the number of citations (Table 2), American Journal of Respiratory and Critical Care Medicine leads with 3,244 citations, followed by European Respiratory Journal (2,144), Thorax (1,405), Journal of Applied Physiology (1,348), and Chest (1,172). Notably, 8 journals fall within the Q1 region of the JCR quartile, and 7 journals boast impact factors - exceeding 5. These include American Journal of Respiratory and Critical Care Medicine (IF=24.7), European Respiratory Journal (IF=24.3), Thorax (IF=10), Chest (IF=9.6), American Journal of Clinical Nutrition (IF=7.1), Journal of Cachexia, Sarcopenia and Muscle (IF=8.9), and NEJM (IF=158.5). In comparison with the earlier journal analysis, the co-cited top journal exhibits a notable increase in JCR quartile, indicative of the study’s scientific rigor and robust theoretical foundation.

Table 2 Top 10 Cited Journals Related to COPD with Sarcopenia

Analyzing the relationship of citations between journals and co-cited journals performed using CiteSpace software through a dual-map overlay of journals.19 The yellow and green lines represent primary application paths. The yellow lines indicate research published in journals focused on molecular, biology, and immunology, with main citations found in molecular, biology, and genetics journals. The green lines signify research published in journals focused on medicine, medical, and clinical, with main cited studies found in molecular, biology, genetics, health, nursing, and medicine journals (Figure 5).

Figure 5 Dual-map overlay depicting journals related to COPD with sarcopenia.

Authors and Co-Cited Authors

A total of 3,828 authors were identified through the publication search, forming a cooperation network with those who have published at least 5 (n=60) papers. Table 3 highlights the top three authors with a minimum of 20 publications. Schols Annemie MWJ exhibits the largest nodes based on publication count. And a close cooperation was observed between Schols Annemie MWJ and Gosker Haary R, Barreiro Esther and Gea Joaquim, Polkey Michael I, Kemp Paul R and Hopkinson Nicholas S, Wouters Emiel FM and Spruit Martijn A, Maltais Francois and Debigare Richard, and (Figure 6A).

Table 3 Top 10 Authors and Co-Cited Authors Related to COPD with Sarcopenia

Figure 6 Network visualization map for authors and co-cited authors.

Notes: (A) authors and (B) co-cited authors related to COPD with sarcopenia.

Among the 20,180 co-cited authors, 18 received more than 100 citations in relevant publications. The highest number of co-citations (n=392) belongs to Schols Annemie MWJ, followed by Barreiro Esther (n=355) and Gosker Haary R (n=242). Figure 6B illustrates the co-citation network graph, analyzing authors with ≥80 co-citations. Positive cooperative relationships among various co-cited authors are indicated, featuring pairs such as Schols Annemie MWJ and Gosker Haary R, Schols Annemie MWJ and Engelen Marielle PKJ, Barreiro Esther and Maltais Francois, as well as Anker SD and Von Haehling S.

Publications and Co-Cited References

The analysis of publications in WoS (Table 4) revealed that 4 out of 758 publications received citations exceeding 500. Among the top 10 cited articles, the majority focused on pathogenesis and prognosis related to sarcopenia.

Table 4 Top 10 Cited Articles Related to COPD with Sarcopenia

In the domain related to COPD with sarcopenia, a cumulative total of 28,551 co-cited references were identified, simultaneously cited by other publications. Table 5 lists the top 10 co-cited references concerning COPD with sarcopenia, each with a minimum of 63 co-citations.28–37Figure 7 presents the co-citation network diagram,6,28–56 analyzing references with ≥42 (n=30) co-citations. Notably, “Marquis K, 2002, Am J Resp Cri Care”28 exhibits active co-citation relationship with “Swallow EB, 2007, thorax”.31 Among the top 10 co-cited references, the predominant focus is on body composition (skeletal muscle mass), mortality and clinical correlates in COPD.

Table 5 Top 10 Co-Cited References Related to COPD with Sarcopenia

Figure 7 Visualization results of co-cited references related to COPD with sarcopenia.

References with Citation Bursts

The red bar in Figure 8 signifies citation bursts, indicating an increased number of citations in a specific field at a particular time. Using CiteSpace software, we identified 10 references with significant citation bursts.6,11,14,32,37,47,51,56–58 Furthermore, we delineated the minimum burst duration in relation to COPD with sarcopenia research. As depicted in the figure, the earliest and latest citation bursts occurred in 2012 and 2020, respectively. Among these references, “Sarcopenia: revised European consensus on definition and diagnosis” (authored by Cruz-Jentoft AJ et al) exhibited the strongest citation burst (strength = 17.82), observed between 2019 and 2022. In summary, the burst strength of the top 10 references varied between 9.33 and 17.82, with durations ranging from 1 to 4 years. We condensed the primary research content of the 10 references with the strongest citation bursts and presented it in Table 6.

Table 6 Main Content of Top 10 References with Strong Citations Bursts Related to COPD with Sarcopenia

Figure 8 Top 10 references with strongest citation bursts related to COPD with sarcopenia.

Keywords Analysis for Hotspots and Frontier Research Areas

Table 7 presents the top 20 frequent keywords related to COPD with sarcopenia. These terms such as COPD and sarcopenia represent key directions for future research. Additionally, keywords, like inflammation, frailty, exercise, rehabilitation, nutrition, malnutrition, and computed tomography, point to areas of mechanistic, diagnostic, and therapeutic investigation in the context of COPD with sarcopenia. The keyword cluster is analyzed using VOSviewer software for network visualization and overlay visualization map (Figure 9). Each keyword is represented as a circle, with the circle size indicating the keyword’s frequency and the line thickness reflecting the correlation between keywords (Figure 9A) The various colors of circles for keywords and lines denote hotspots and frontier research areas in recent years (Figure 9B).

Table 7 Top 20 Keywords Related to COPD with Sarcopenia

Figure 9 Cluster analysis of keywords related to COPD with sarcopenia.

Notes: (A) Network visualization map (B) Overlay visualization map for keywords.

Figure 9A reveals four clusters suggesting four primary research directions in the field. The red cluster encompasses cachexia, muscle atrophy or wasting, inflammation and oxidative stress. The green cluster encompasses body composition, nutrition or malnutrition, rehabilitation or pulmonary rehabilitation, and mortality. The blue cluster encompasses aging, frailty and osteoporosis. The yellow cluster encompasses computed tomography, emphysema, muscle mass. Figure 9B indicates that the yellow-green cluster represents hotspots and frontier research areas in recent years, including frailty, mortality, computed tomography and osteoporosis.

Discussion

This study is the first scientometric analysis examining crucial findings, research focal points, and frontiers in COPD with sarcopenia. Our comprehensive review covered 758 articles and reviews. Over the past two decades, literature on COPD with sarcopenia has seen a consistent rise, notably increasing since 2013, signifying a growing emphasis on this subject. Sarcopenia, as a notable comorbidity in COPD, is poised to become a pivotal research direction in the future.

Our scientometric analysis identified the USA, Netherlands, and England as the top three countries conducting research on COPD with sarcopenia., revealing close collaboration among developed countries. Furthermore, all of the top 10 affiliations were from these developed nations, emphasizing extensive cooperation. Nearly half of the total publications focused on respiratory system, geriatrics gerontology and gerontology. Other categories indicated the common occurrence of COPD with sarcopenia alongside other diseases, emphasizing the complexity of the topic, and the necessity for comprehensive treatment.

International Journal of Chronic Obstructive Pulmonary Disease emerged as the most published journal, with notable journals like American Journal of Respiratory and Critical Care Medicine (IF=24.7, Q1) and European Respiratory Journal (IF=24.3, Q1) boasting impact factors exceeding 20. The majority of studies were published in co-cited academic journals within the Q1 region of the JCR quality, indicating their significant influence on future directions.

Current research on COPD with sarcopenia predominantly appears in two types of journals: those focusing on molecular biology and immunology and those concentrating on medicine, medical, and clinical subjects. This observation indicates increasing recognition of COPD with sarcopenia, suggesting a surge in both bench and clinical research in this field.

COPD and sarcopenia are prominent keywords, with additional terms indicating ongoing research focus and potential future areas of interest. Notably, COPD patients commonly develop skeletal muscle loss or sarcopenia, as confirmed by prior human studies.11,59,60 Further keyword cluster analysis reveals hotspots and frontier research areas (Figure 9B), highlighted by keywords: 1) Computed tomography, frailty and mortality. Sarcopenia, defined by low muscle strength, quantity or quality is typically assessed through bioelectrical impedance analysis (BIA), considered the gold standard for body composition measurements. Given the widespread use of chest computed tomography (CT) is widely used for lung assessment in COPD, concurrent measurement of the pectoralis muscles has emerged as a modality for sarcopenia evaluation. Validity in utilizing pectoralis muscle (PM) cross sectional area (CSA) from CT assessing skeletal muscle mass (SMM) in individuals with COPD has been established.61 A cross-sectional study demonstrated the feasibility of CT scans to assess erector spinae muscle (ESA) size, particularly in male and obese individuals undergoing health checkups, showing a strong correlation with BIA.62 Additionally, quantitative measurement of thoracic skeletal muscle area on chest CT scans, including CSA of PM, latissimus dorsi (LAT), and erector spinae muscle (ESM), is associated with lung function, radiologic signs of emphysema, and clinical outcomes in COPD, indicating the value of CT-derived measurements in detecting impaired muscle quantity and quality, predicting COPD severity.63–66 Furthermore, COPD patients undergoing lung transplant (LTx) typically experience muscle loss or sarcopenia in end-stage lung disease progression, with lean dorsal muscle area from CT scans linked to survival rate.67 The pectoralis muscle index (PMI) and adipose tissue demonstrated by chest CT are also associated with mortality in COPD patients, including subcutaneous adipose tissue (SAT) and intermuscular adipose tissue (IMAT).10 As reported in previous human studies, progressive COPD patients often experience pulmonary cachexia (PC),68 and those with sarcopenia suffer adverse clinical outcomes including frailty69–71 and mortality.10,63,72 Physical frailty and sarcopenia exhibit extensive clinical similarities and share inflammatory biomarkers (eg IL-6), bridging the inflammation gap between COPD and sarcopenia.73 Despite the prognostic significance of CT-body composition in COPD confirmed by the aforementioned studies, additional comprehensive research is needed due to the diverse nature of body composition assessments and clinical outcomes.92) Osteoporosis. In the context of COPD, characterized by airflow obstruction and respiratory symptoms, patients exhibit multimorbidity. Beyond the association with muscle or sarcopenia, COPD is intricately linked to bone health, namely osteoporosis. This association amplifies the risk of fragility fractures, increases the rate of hospitalization, elevates the burden of disease, and detrimentally affects overall quality of life.74,75 The development of osteoporosis in COPD patients is influenced by factors including corticosteroid treatment, systemic inflammation, smoke exposure, low physical activity, malnutrition, and sarcopenia.3,74,76 Sarcopenia’s presence significantly reduces bone mineral density (BMD) in mild COPD patients, and severe sarcopenia is associated with osteoporotic fractures in 9.9% of stable COPD patients,77,78 underscoring the potential contribution of bone-muscle crosstalk to osteoporosis and sarcopenia risk in this population. Osteoporosis and sarcopenia, as common risk factors for COPD, share underlying pathogenic mechanisms. Beyond mechanical interactions, muscle and bone act as endocrine organs, regulating each other’s functions.75 Notably, IL-6, fibronectin type III structural domain-containing protein 5 (FNDC5)/irisin, myofibrillar growth factor, RANKL/RANK, and osteocalcin play potential roles in the pathogenesis of sarcopenia and osteoporosis in COPD patients. This suggests a musculoskeletal crosstalk mechanism contributing to the comorbidities in COPD.76 Similar to the predictability of thoracic skeletal muscle CSA for sarcopenia, evidence indicates that BMD from chest CT can also serve as a convenient surrogate marker for osteoporosis, facilitating timely interventions and preventative care.79,80 Additionally, the concept of osteosarcopenic adiposity (OSA) syndrome or osteosarcopenic obesity (OSO) has emerged, denoting the concurrent deterioration of bone (osteopenia/osteoporosis), muscle (sarcopenia), and adipose tissue expansion. This syndrome has a prevalence of 8% in middle-aged and older adults globally, with a higher burden among females and older adults.81,82 Although the available evidence on the multilevel interactions between osteosarcopenia and COPD is summarized, further in-depth research in this area is warranted.833) Nutrition, exercise, and rehabilitation. The evolving understanding of the relationship between sarcopenia and COPD underscores shared treatment modalities, notably nutritional support, resistance exercise (RE), and pulmonary rehabilitation (PR).84,85 The nutritional status of COPD patients with sarcopenia emerges as a significant concern. Oral supplementation with protein, micronutrients, fat, or a combination thereof has demonstrated efficacy in enhancing muscle strength and physical performance in these individuals.25,86 While vitamin D has received more attention in the context of bone health, the role of vitamin K, often overlooked, presents a potential link between COPD, osteoporosis, and sarcopenia, with associations noted in cross-sectional studies.87 Muscle dysfunction and wasting stand out as prominent extra-pulmonary effects of COPD. Decreased activity leads to muscle mass reduction, culminating in inefficient oxygen utilization and establishing a detrimental cycle of exercise capacity deterioration. Presently, PR is recognized as a crucial measure to enhance lung function in COPD patients, while RE proves to be the most effective intervention for improving quality of life for sarcopenia in older people.88,89 Further exploration of muscle-bone crosstalk in the context of nutrition and physical activity in COPD with sarcopenia holds promise for unveiling novel non-pharmacological management modalities in a condition that lacks a pharmacological cure.

Scientometric analysis serves as a descriptive and quantitative tool, offering a more evidence based assessment of the current state of research fields compared to traditional narrative commentary. In our study, we scientometricly analyzed the articles and reviews related to COPD with sarcopenia using a bibliometrics approach. The analysis, grounded in available data, furnishes comprehensive insights and trends, intending to serve as a guide for fellow researchers in the field. However, certain inherent limitations must be acknowledged. Our search was confined to the WoS Core Collection database, and we exclusively considered English literature published within the two decades. Besides, the quality of publications did not be evaluated comprehensively, with all publications contributions accorded equal weight. And VOSviewer software, employed for extracting author names and thesaurus terms for keywords, may encounter challenges when dealing with variations in spellings or multiple author names and thesaurus terms, potentially affecting the accuracy of scientometric analysis and visualization. It is imperative to recognize that while the WoS Core Collection is an authoritative and comprehensive database, and tools like VOSviewer and CiteSpace are widely used software, their utilization introduces potential biases and limitations.

In conclusion, the study provides insights into the status during the past 2 decades and research trends in the future related to COPD with sarcopenia. Statistical analysis of scientometrics holds promise in guiding future preclinical and clinical studies in the field.

Data Sharing Statement

The raw data supporting the conclusion of this article will be made available by the authors, without undue reservation.

Acknowledgments

We express our gratitude to all the researchers who took part in the study related to COPD with sarcopenia.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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