Publication trends of research on acute lung injury and acute respiration distress syndrome during 2009-2019: a 10-year bibliometric analysis

Abstract

Background: Acute lung injury (ALI) is a common disease that usually progresses to acute respiratory distress syndrome (ARDS) with high morbidity and mortality. We aim to analyze the trends in ALI/ARDS, and to compare the differences in aspects of years, countries, institutions, journals, etc. Methods: We screened all relevant literature on ALI/ARDS from Web of Science during 2009-2019, and analyzed the research trends in this field by VOSviewer. Results: We had screened 7,890 publications with a total cited frequency of 164,713. The United States contributed the largest number of publications (2,612, 33.11%), cited frequency (81,376, 48.61%), and the highest H-index (107). Journal of Critical Care Medicine published the largest number of literatures on ALI/ARDS, MATTHAY MA published the majority of articles in this field (147), while SLUTSKY AS received the most cited frequency (10015). University of California San Francisco had the largest number of publications (243, 3.08%) among all full-time institutions. In the aspect of clinical research in ALI/ARDS, the keyword “Berlin definition” emerged in recent years, with an average year of 2016.3; in the basic research, the key word “protects” appeared latest, and the average years were 2016.5. The current research trend indicates that basic research is gradually transforming into clinical research. Conclusions: The United States have made the most significant contribution to the ALI/ARDS field in the last decade. The current research ‘hotspot’ mainly appeared in clinical research, such as “Berlin definition”. In regards to basic research, studies tend to explore the protective mechanisms against ALI/ARDS.

Introduction

Acute lung injury (ALI) is a severe lung injury caused by variety of direct or indirect factors, and often progresses to acute respiratory distress syndrome (ARDS) [1,2]. The typical pathological and physiological characteristics of ALI include decreased lung volume, reduced lung compliance and low ventilation/blood flow ratio [3], with notably high morbidity and mortality [4]. In 2005, the morbidity of ALI in the United States is 78.9/100,000 and the mortality rate is 38.5% [5]. At the end of 2019, a novel coronavirus-infected pneumonia has spread quickly in China. According to newest report on the clinical characteristics of 138 hospitalized patients in Wuhan, China, 36 patients were transferred to the intensive care unit (ICU) because of complications, among them the most common complication was ARDS (22 [61.1%]) [6].

Causes of ALI include pulmonary factors (direct injuries) and extrapulmonary factors (indirect injuries). Traditional treatment for ALI/ARDS includes the control of primary disease, inflammatory reaction inhibition, respiratory support, fluid management, hormone therapy, etc [7]. In recent years, in the help of research, growing number of studies have confirmed the effectiveness of intervention measures. Drug treatments reduce lung injury by regulation of signal pathways. For instances, p-coumaric acid alleviates LPS-induced lung injury in rats by scavenging ROS [8], and protein Kinase C can reduce LPS-induced lung injury in mice via the Notch Signaling Pathway by suppressing Th17 cell response [9], and resveratrol inhibits neutrophil activation and Src family kinases activity thereby alleviating lung injury [10]. The current research mainly focuses on the animal studies or preclinical work, and there are no clear or effective illustrations of treatment strategy for ALI. To explore the potential targets, we tried to review the recent research trends and predict the potential future hotspot.

Bibliometric analysis is often used to indicate the trend of time changes in a certain research field, and make qualitative and quantitative analysis of scientific journals and books, contributing greatly to disease treatment and the development of clinical guidelines [11-13]. Besides, the advantage of bibliometrics is not only a reflection on publishing trends, but also an indication for the future research hotspots. It has been widely used in the current medical research such as sepsis [14], osteoarthritis [15] and cancer [16]. In this study, we conducted bibliometric to analyze the ALI/ARDS based on Web of Science (WOS), to clarify the research progress and trend nowadays and speculate the future hotspots of ALI/ARDS.

Materials and methods

Data sources and search strategies

We made use of the Web of Science which is widely accepted in bibliometric analysis, to conduct a comprehensive online search on ALI/ARDS from 2009 to 2019. All data were collected online and no ethical proof was required. All searches were conducted on November 27, 2019 to avoid bias of database renewal. The search strategies were shown as follows, TS: (“acute lung injury”) OR TS: (“acute lung injuries”) OR TS: (“acute lungs injury”) OR TS: (“acute lungs injuries”) OR TS: (ALI) OR theme: (ARDS) OR TS: (“acute respiratory distress syndrome”) OR TS: (“acute respiratory distress syndromes”) AND language: (English). Furthermore, peer-reviewed articles were reserved, and all other categories were excluded. The screening process is shown in Figure 1.

Figure 1.

The flow chart of screening process in the research of ALI/ARDS.

Data collection

Two authors (CW and XRW) independently extracted all data from included articles, including titles, keywords, authors, institutions, journals, dates of publication, countries/regions, citations, H-index, etc. Then we analyzed the data using GraphPad Prism 6 and VOSviewer.

Bibliometric analysis

We used the WOS to describe the characteristics of included publications. The relative research interest (RRI) was defined by the number of publications associated with a particular research field, and then was divided by the number of publications per year in all fields [17,18]. The impact factor (IF) was acquired in the newest edition of the journal citation report (JCR). H-index, which widely accepted as a reflection of research influence among scientists or countries, means scientists or countries have published “H” papers and the papers have been cited in other publications for at least “H” times [19,20].

The relationship between highly cited references and prolific authors was analyzed using VOSviewer software, which maps the network of keywords which associate with ALI/ARDS and classifies keywords into several clusters with colors according to the co-occurrence times. The average appearing year (AAY) was used to describe the relative novelty of keywords [21].

Results

Global contribution to publications on ALI/ARDS

Referred to the inclusion criteria, 7,890 articles related to ALI/ARDS were included in our study. The ranking of the origin of those publications are as listed: first, USA (2,612, 15.02%); second, China (2,480, 14.27%); third, Germany (650, 3.74%); fourth, Canada (424, 2.44%); fifth, Japan (397, 2.28%). According to the annual number of publications, the largest number appeared in 2016 (only period from January to November were counted in 2019 and the data were not taken into account in the ranking) (Figure 2A). By calculating the RRI value, we found in the year 2012 there are the highest number of publications related to ALI/ARDS (Figure 2B). As for the contribution from each nation, in 2009 the articles from China was considerably less than from the United States, but in 2016, China began to surpass the United States, ranking first in the number of publication.

Figure 2.

Articles related to ALI/ARDS published worldwide. A. The number of publications, citation frequency (actual value × 0.05), and H-index (actual value × 5) in the top 20 countries or regions; B. The annual publications worldwide and in top 3 countries, and the relative research interest of ALI/ARDS. Polyline represents the relative research interest every year.

Citations and H-index analysis

We analyzed the screened publications from 2009 to 2019 through Web of Science as shown above. All publications related to ALI/ARDS were cited 164713 times (excluding self-citation, 128862), with an average of 20.88 times per article. The United States ranked the first, with 49.40 percent, 81,376 citations (excluding self-citation 73108), and the H-index was 107. The second most-cited country was China, 31996 (excluding self-citation, 26075), and the H-index was 62. Germany ranked the third, although there were only 650 publications, it contributed 20,797 citations (excluding self-citation, 19846), with H-index of 57 (Figure 2A).

Growth trend of publications

To visualize the cumulative volume of global and country publications, we plotted the growth curve in Figure 3. We found that, except for China, the volume of publications among global, USA and Germany were linearly correlated (Figure 3A, 3B and 3D). China, in contrast, showed an exponential growth, which has been gradually climbing since 2016 (Figure 3C).

Figure 3.

The trend of annual publications related to ALI/ARDS among worldwide and top 3 countries. A. Global; B. USA; C. China Mainland; D. Germany.

Journals publishing researches on ALI/ARDS

The top 20 journals accounted for 30.14% (2665) of all publications on ALI/ARDS. Specifically, Critical Care Medicine (IF 6.97) ranked the first with 295 publications, and PLOS ONE with 223 articles went after. And, American Journal of Physiology Lung Cellular and Molecular Physiology (IF 4.06), Critical Care (IF 6.96) and International Immunopharmacology (IF 3.36) ranked third, fourth and fifth place, respectively, with the total number of 212/195/168. The number of publications ranked the fifth and the tenth showed a mild drop, from 168 to 140. The top 20 journals were listed in Figure 4A.

Figure 4.

Articles published in different journals and institutions on ALI/ARDS. A. The top 20 journals by the amount of publications related to ALI/ARDS; B. The top 20 institutions categorized by the amount of publications related to ALI/ARDS.

Institutions publishing researches on ALI/ARDS

University of California San Francisco in the United States had the largest number of publications among all full-time institutions, with 243 publications, accounting for 3.08% of the total. The second, Toronto University in Canada, produced 230 publications, accounting for 2.92% of the total. The Harvard University in the US ranked the third with 199 publications, accounting for 2.52%. Among the top 20 institutions, majority (11) of institutions are from the United States, followed by China and Canada, with 6 and 2 institutions respectively, and Brazil with 1 institution ranked the forth. The top 20 journals published the most papers were listed in Figure 4A and 4B.

Authors publishing researches on ALI/ARDS

All the top 10 authors contributed a total number of 799 publications, which takes 10.13% of the total. MATTHAY MA (Univ Calif San Francisco) ranked the first with 147 publications, followed by WANG Y (Zhejiang Univ) and ZHANG Y (Cent S Univ) from China, with 81 and 79 articles, respectively. Among the top 10 authors, there are 4 Americans, 3 Chinese, 2 Canadians and 1 Italian. Details are showed in Table 1.

Table 1.

Top 10 authors with most publications in research scope of acute lung injury

Author	Country	Affiliation	No. of Publications	No. of Citations
MATTHAY MA	USA	Univ Calif San Francisco, Med Ctr Parnassus, Dept Med	147	8444
WANG Y	CHINA Mainland	Zhejiang Univ, Coll Pharmaceut Sci	81	1429
ZHANG Y	CHINA Mainland	Cent S Univ, Subei Peoples Hosp Jiangsu Prov	79	1453
PELOSI P	Italy	Univ Genoa, IRCCS San Martino Ist Nazl Ric Canc	76	1846
LI Y	CHINA Mainland	Liaoning Canc Hosp & Inst, Dept Gen Surg	75	1589
CALFEE CS	USA	Univ Calif San Francisco, Dept Med	73	3084
THOMPSON BT	Canada	Univ Toronto, Interdept Div Crit Care Med	72	9102
GAJIC O	USA	Mayo Clin	68	4601
WARE LB	USA	Vanderbilt Univ, Med Ctr, Dept Med	65	3004
SLUTSKY AS	Canada	Univ Toronto	63	10015

In the rankings of reference quantity, the Acute Respiratory Distress Syndrome, the Berlin Definition on Jama-Journal of the American Medical Association (IF 51.27) by Rubenfeld GD ranked the first with 2938 citations, followed by Papazian L and Herridge MS, with 1091 and 1050 citations respectively. Details are showed in Table 2.

Table 2.

Top 10 high-cited papers related to acute lung injury

Title	Corresponding authors	Journal	Publication Year	Total Citations
Acute Respiratory Distress Syndrome The Berlin Definition	Rubenfeld, GD	JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION	2012	2938
Neuromuscular Blockers in Early Acute Respiratory Distress Syndrome.	Papazian, L	NEW ENGLAND JOURNAL OF MEDICINE	2010	1091
Functional Disability 5 Years after Acute Respiratory Distress Syndrome	Herridge, MS	NEW ENGLAND JOURNAL OF MEDICINE	2011	1050
Pneumonia and Respiratory Failure from Swine-Origin Influenza A (H1N1) in Mexico	Perez-Padilla, R	NEW ENGLAND JOURNAL OF MEDICINE	2009	1047
Prone Positioning in Severe Acute Respiratory Distress Syndrome	Guerin, C	NEW ENGLAND JOURNAL OF MEDICINE	2013	1002
Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries	Laffey, JG	JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION	2016	983
Extracorporeal Membrane Oxygenation for 2009 Influenza A(H1N1) Acute Respiratory Distress Syndrome	Davies, A	JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION	2009	908
H1N1 2009 influenza virus infection during pregnancy in the USA	Jamieson, DJ	LANCET	2009	872
Higher vs Lower Positive End-Expiratory Pressure in Patients With Acute Lung Injury and Acute Respiratory Distress Syndrome Systematic Review and Meta-analysis	Meade, M	JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION	2010	716
Factors Associated With Death or Hospitalization Due to Pandemic 2009 Influenza A (H1N1) Infection in California	Louie, JK	AMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION	2009	710

Analysis of keywords in ALI/ARDS

We analyzed all included 7,890 articles using the VOSviewer. In Figure 5A, 159 keywords (defined as terms that occurred more than 75 times appeared in titles and abstracts in all publications) were divided into 2 groups: “clinical research” (left, in red) and “basic research” (right, in green). In clinical research, the keywords with the highest frequency are: acute respiratory distress syndrome (1387 times), ARDS (1166 times), mechanical ventilation (870 times), mortality (799 times) and injuries (517 times). In the basic research, the words are: acute lung injuries (3696 times), respiratory-distress-syndrome (2301 times), inflammation (1555 times), expression (1043 times) and activation (909 times). Detailed showed in Supplementary Table 1.

Figure 5.

The mapping of keywords in ALI/ARDS studies.

The distribution of keywords in different time periods were indicated (Figure 5B). Chronological order is presented from dark blue to bright yellow. In cluster 2, the earliest keywords were “expression” (cluster 2, AAY 2009.0) with 1043 times, the latest words were “protects” (cluster 2, AAY 2016.5) with 155 times. In cluster 1, the earliest words were “mechanical ventilation” (cluster 1, AAY 2009.4) 870 times, and the latest word was “Berlin definition” (cluster 1, AAY 2016.3) with 161 times. Referring to the color intensity, we found that the research hotspot on ALI gradually shifted from the basic research to clinical treatment in recent years (Figure 5B).

Discussion

In the present study, we reviewed 7890 papers on ALI/ARDS, and found the number of global publications per year increased gradually and rapidly (Figure 3). The major finding was that the USA was the most productive and published most highly cited studies, resulting a much higher H-index than other countries (H-index: 107) (Figure 2A). Besides, in the top 10 authors with most publications in research scope of acute lung injury, 4 were American researchers (Table 1) and 11 in 20 in the top 20 institutions were from USA (Figure 4B). However, China was noteworthy of the rapid growth, and the publication number has surpassed the USA since 2016 (Figure 2B). For journals, Critical Care Medicine was the most popular journal and published 295 articles, which accounts for 3.74% (Figure 4A). The top 10 high-cited papers related to ALI/ARDS, all published in the most famous clinical journals (New England Journal of Medicine, JAMA, and Lancet) (Table 2). What’s more, keywords extracted from the titles and abstracts were stratified into two major clusters “Basic Research” and “Clinical Research” (Figure 5A) by VOSviewer software and a research trend indicated that basic research was gradually transforming into clinical research (Figure 5B). Furthermore, “berlin definition”, “stromal cells” and “protects” might be the latest potential ‘hotspots’ in the research of the ALI/ARDS (Supplementary Table 1).

Since ARDS was originally defined in 1967 with a case report in critically ill patients, considerable researches have been made to explore the pathogenesis and pathophysiology of the ALI [7,22,23]. In the past decade, the number of publications every year in the field of ALI/ARDS increased stably due to its high mortality at 30-40% [24]. However, as for the trend of RRI in ten years, the curve shows a downward trend in volatility overall (Figure 2B). Nowadays, the management of ARDS patients mainly focuses on a lung-protective ventilation strategy and no specific pharmacotherapies have been formulated [24], which may weaken the researchers’ interest, confidence and persistence on the disease to some extent. In support, it is evident shown in the RRI curve that there was a sharp increase in 2012 (Figure 4A). During that time, the Berlin definition [25] was a milestone for the identification and diagnosis of ARDS and contributed the progress of related research, which is consistent with high-cited papers entitled “Acute Respiratory Distress Syndrome: The Berlin Definition”. It is the top 1 high-cited papers related to ALI with the total citations of 2938, much more than other articles (Table 2). The research results suggest that the proposal of guidelines or definitions will help promote the progress and development of research in this field. Therefore, regarding ALI/ARDS research, we should continue to enrich its definitions and guidelines.

As to the country contribution, the USA was the most productive region and has made the greatest contribution in researches on ALI/ARDS, evidenced by the number of publications, H-index, and citation frequency. Moreover, in the top 10 authors with most publications (Table 1), four of them were American, which may promote the ALI/ARDS research advancement in America, the same publication trend can also be documented in other diseases and related research, such as osteoporosis [26], diabetes [27], pancreatic diseases [28], etc. Given the fact that the diagnostic criteria of ARDS was initially defined by American and European scholars on the American-European Consensus Conference (AECC) in 1994 [29], when the diagnosis of ARDS were made scientific. The USA focused on this disease or issue earlier than the rest of the world, this also explains why it is by far the most publicized country. Although Chinese scholars did not participate in the proposal of standards and started late in the studying the disease, the number of publications ranked second and two Chinese scholars were among the top 10 authors with most publications (Table 1). Large population base determines higher number of ARDS-related patients, for example, a cross-sectional study in 20 participating Chinese ICUs enrolled 1,814 patients found 149 (8.2%) and 147 (8.1%) patients were diagnosed of ARDS by AECC and Berlin definition, respectively [30]. A study retrospectively analyzed 925 preterm infants with respiratory distress in China mainland and the number of ARDS infants was 49, which accounted for 5.29% [31]. Therefore, gradually accumulated relevant diagnosis or treatment experience have promoted the research of the disease, explaining why the annual publications related to ALI/ARDS in China sustained a rapid growth and has exceeded the USA since 2016 (Figure 3). However, we cannot deny the fact that China has not achieved high citation frequency or high H-index as the USA (Figure 2A). The imbalance between the quantity and quality of publications in China might attribute to several reasons. Firstly, the number of publications in China mainland was much less than that in the USA and German in 2009, under the global trend (Figures 2 and 3), and it is evident the Chinese research on the ALI/ARDS started relatively later. Secondly, ARDS is a disease diagnosed from clinical symptoms based on clinical evidences. China reports relatively more on observational studies with lack of high-quality multicenter Randomized Clinical Trials (RCTs), leading to insufficient solid evidences in clinical practices. Thirdly, there are many other studies in China on the therapeutic effect of traditional Chinese medicine in ALI/ARDS. For instance, Yam glycoprotein, separated from traditional Chinese yam, has anti-inflammatory and immunomodulatory effects on the lipopolysaccharide (LPS)-induced ALI mice [32]. A study enrolled 53 patients in ICU with ARDS to observe the effects of Xuanbai Chengqi decoction on lung compliance [33]. There is no doubt that the utilization of traditional Chinese medicine provides new options for clinical treatment of ALI/ARDS, but traditional Chinese medicine is difficult to be verified by modern medicine, due to its multi-component, multi-target and mostly unknown mechanisms. ALI/ARDS is common cause of respiratory failure and associated with several clinical disorders including sepsis, trauma, pneumonia, and aspiration. Therefore, the study of the disease requires multidisciplinary communication and cooperation, which are not limited to a certain country/region or individual researchers.

Among the top 20 institutions, The USA owned 11 institutions from the top 20 institutions in researches with regard to ALI/ARDS, followed by Canada, China, France and Brazil, indicating its dominant role in this field (Figure 4B). University of California San Francisco that had published the most articles in such area belonged to USA. and two authors (MATTHAY MA and CALFEE CS) who were top 10 authors with most publications are from the same university (Table 1). The United States possesses the most elite institutions around the world, which in turn supports its leading position. Besides, there were 6 institutions in China and 2 in Canada as well, and the rank was roughly consistent with publications numbers that from the USA (rank 1), China (rank 2), Canada (rank 4) (Figure 2A). Regions and institutes play a vigorous ongoing role for further publications [34], thus, more elite institutions are to be built to improve the international status in the significant directions associated with ALI/ARDS, and still, partnerships among top institutes/regions could be a good choice.

Of note, the journal of Critical Care Medicine had published 295 papers in the field, ranking the first. Critical Care Medicine mainly publishes clinical and basic research in critical illness, and ARDS as a respiratory failure is common in critical ill patients, which is in line with the journal aims and scopes. According to a cross-sectional research of 29,144 patients from 50 countries [35], the prevalence of ARDS in ICU patients was 10%, and ARDS was identified in 23% of all ventilated patients. The same reason is applied for the journal of Critical Care (rank 4). PLOS One ranks second and is a comprehensive journal, which is well known for its big publication numbers, for example, it has published 19,150 papers in 2018 according to WOS. American Journal of Physiology Lung Cellular and Molecular Physiology (rank 3) and International Immunopharmacology (rank 5) mainly focused on basic research. Mature animal models such as LPS, pulmonary ischemia, oleic acid-induced model have been developed for basic research in ALI [36]. Meanwhile, the number of publications ranking at the fifth drops from 168 to 140 as of at the tenth (Figure 2A), and it suggests that future focus is more likely to be published in the aforementioned journals.

High-cited papers lead to tremendous academic impact. The detailed information about the top 10 cited publications within ALI/ARDS are listed in Table 2. The paper entitled “Acute Respiratory Distress Syndrome: The Berlin Definition” had been cited for 2938 times, which was the most cited papers. This study is published on JAMA in 2012 and introduced the evolution from “AECC Definition” to “The Berlin Definition” in detail. Compared with the AECC definition, this Berlin Definition combined consensus discussions with empirical evaluation to form evidence-based, critical illness syndrome definitions accurately, with better predictive validity for mortality [25]. A clinical study that rank second entitled “Neuromuscular Blockers in Early Acute Respiratory Distress Syndrome” is published in the New England Journal of Medicine. This study was a multicenter, double-blind trial that included 340 patients with an onset of severe ARDS to explore the role of neuromuscular blocking agent on 90-day survival rate [37]. All the top 10 high-cited articles were about clinical researches and were published at the top 4 most influential clinical journals (Table 2), highlighting the essence of the ARDS: a clinical presentation in critically ill patients [24].

To explore the research tendency and latest hotspot, visualized mapping portrayed by VOSviewer was applied. In the past decades, keywords were divided into 2 groups: “clinical research” and “basic research” (Figure 5). In the basic research, the pathophysiology of ALI/ARDS, and the mechanisms of injury were explored. There were two main directions [7]: dysregulated inflammation following the activated innate immune response by DAMPs (Danger-Associated Molecular Patterns) [38] and alveolar barrier disruption that increased permeability of microvascular barriers or low rate of alveolar fluid clearance, resulting in accumulation of protein-rich edema fluid [39]. The fundamental mechanisms of ALI/ARDS remain elusive, despite of more than 50 years of research [40]. Therefore, this study suggests that in view of the complex pathophysiological mechanism of ALI/ARDS, researchers should start from the mechanism and establish a unified cell and animal model. Clinically, the content of research covers various aspects including definition, diagnosis, histopathology, pathophysiology, therapeutic methods, etc [1]. Especially, treatment has been optimized for the refinements in ventilator and fluid management [41], supported by evidence from prospective randomized trials. Interestingly, a gradual shift in terms of focus from the “basic research” to the “clinical research” appeared in the time-period map (Figure 5B). Although several models of experimental ALI/ARDS have been developed, none have fully captured the etiologies, initial inflammation, heterogeneity of human ARDS [40]. Instead, more and more high quality clinical researches have provided insights and understanding. However, the importance of basic research is not to be ignored. ARDS is a syndrome with a broad clinical phenotype including mild, moderate and severe, and it has been challenging to translate the results of animal and cell studies to pharmacologic therapies [7], This is also a key issue restricting the progress of basic research. For example, potentially targetable inflammatory mediators, beneficial in basic research, could not be applied on the clinical ill patients. In the future, optimized design of ALI/ARDS studies is essential for ongoing interaction among basic scientists, clinicians and translational scientists.

The keyword “protects” appeared most recently with an AAY of 2016.5 (Supplementary Table 1). Nowadays, effective treatments for patients with ARDS are mainly lung protection strategies, such as the optimization of small tidal volume ventilation. An ongoing RCT (Randomized Controlled Trial) will test the possibility of improving survival by further lowering tidal volume to 4 ml/kg and plateau pressures to 25 cmH₂O. Besides, important signaling pathways or molecules were discovered in basic researches continuously such as that miR-424 overexpression protects alveolar epithelial cells from LPS-induced ALI via the NF-κB pathway. Especially, cell-based therapy has emerged promising for the treatment of ALI/ARDS, which is also confirmed in our study with the third newest keyword “stromal cells”. Bone marrow-derived stromal cells have been shown to enhance recovery from lung injury, and increasing ATP concentration in alveoli and mesenchymal stromal cells (MSCs) have demonstrated putative effects on experimental ARDS. Therefore, the results of this study prompts that the direction of follow-up research may mainly focus on the protection of organs, maintaining and protecting lung function through cell therapy and mechanical ventilation etc. In “clinical research” cluster, “Berlin definition” is the newest word (Supplementary Table 1). The definition of the ARDS has always been controversial. A study has compared the prevalence and outcomes of pediatric ARDS using PALICC (Pediatric Acute Lung Injury Consensus Conference Criteria) and Berlin definition, suggesting the PALICC criteria identified more number of patients with ARDS. In the future, breakthroughs may be succeeded upon the aforementioned hotspots.

This bibliometric analysis investigated the publications that were extracted from the Web of Science database of Science Citation Index Expanded journals. The data analysis is fairly comprehensive and objective. However, limitations are inevitable. Due to our inclusion criteria, we enrolled publications only in English in the present investigation which may exclude some important non-English studies related to ALI/ARDS. In addition, papers published in 2019 were not all incorporated, which means the analysis did not contain any keywords from 2019. The last but not the least, the database is still open for updating studies continuously, so a slight discrepancy between bibliometric analysis results and actual research situation may exist.

Conclusions

Taken together, the present study has summarized and analyzed the global research trends concerning ALI/ARDS. The USA has made the biggest contribution in regards of number and impact of publications. Although China has produced a considerable quantity of publications with very rapid growth, the quality of these papers are expected to be increase correspondingly (Figure 6). For journals, though Critical Care Medicine was the most popular journal and latest studies, novel progresses were also published in the top 4 clinical medicine journals. In two main clusters, “Basic Research” and “Clinical Research”, several keywords such as “berlin definition”, “stromal cells” and “protects” appear to be the latest potential hotspots in the field of the ALI/ARDS, suggesting possible trends of research focus.

Figure 6.

Publication trends of research on ALI and ARDS.

Disclosure of conflict of interest

None.