Bibliometric Analysis of Lung Transplantation Research Articles

Background: Method: Results: Conclusion:


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In the last 30 years lung transplantation, a surgical procedure in which a patientʼs lungs are replaced (totally or partially) by donor lungs, has proven to be a lifesaving therapeutic option for patients with end-stage cardiopulmonary and septic lung disease. Lung transplantation, based on initial evidence in 1940s and 1950s, has been one of the main achievements in the field of organ transplantations, resulting in an increased life expectancy and better quality of life for those suffering from various lung diseases such as chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis or cystic fibrosis. The first successful transplant surgery involving the lungs was a heart-lung transplant, performed on 9 March 1981 by Dr. Bruce Reitz at Stanford University on a woman with idiopathic pulmonary hypertension [1]. This was followed by the first successful single lung transplant by Joel Cooper (Toronto) in 1986 [2] and the first successful double-lung transplant for cystic fibrosis in 1988 [3]. The evaluation of scientific publications is necessary to acquire information on scientific advances, guide clinical decision making and assess the direction of current research. In spite of its known limitations [4,5], bibliometric analysis contributes greatly to the evaluation of scientific production. One of the major sources for bibliometric information is the Institute for Scientific Information (ISI) Web of Science database. ISI is a multidisciplinary citation database that indexes more than 10 000 high-impact journals in the sciences, social sciences, and arts and humanities. This database collects citations and other academic impact in-Abstract ! Background: In the last 30 years lung transplantation has proven to be a lifesaving therapeutic option for patients with end-stage lung disease. The objective of this study was to perform a bibliometric analysis of lung transplantation research articles. Method: A bibliometric evaluation of the evolution of scientific production in the field of lung transplantations between 1989 and 2009 was conducted using the ISI Web of Science. The search terms selected were "lung transplant*" OR "pulmonary transplant*". Specific features including year of publication, language, geographical distribution, first author, main journal publishing these articles, journals publishing highly cited articles, and institutional affiliation were analyzed. The citation characteristics of articles were additionally analyzed. Results: A total of 6409 (58.0 %) research articles were found. The time trend of the number of ar-ticles showed an increase of more than 6.81 between 1989 and 2009. North America contributed 50.4 % and Europe contributed 46.0 % of published articles. The greatest number of contributions came from the USA (43.6%), followed by England (9.1 %) and Germany (8.6 %). There were 104 522 citations of these articles by 25 July 2010. The average citation per article was 16.31. The New England Journal of Medicine ranked first with regard to the number of articles and the number of highly cited articles. G. A. Patterson, Washington University, and the US National Institutes of Health (NIH) were the top author, institution and funding agency, respectively. Conclusion: The number of publications and the scientific interest in lung transplantation has increased rapidly in recent years. Citations of articles published in the field of lung transplantation are increasing and the numbers of uncited articles are fewer compared to the average citations of articles and uncited articles in the field of medicine.
formation of scientific publications and makes the data available. Many investigators, particularly in the last two decades, have published articles on lung transplantation and related matters, reflecting and facilitating the global propagation of this technique. However, there is currently no analysis of this increasing amount of literature. The objective of this study was to perform a bibliometric evaluation of the evolution of scientific production in the field of lung transplants between 1989 and 2009 based on bibliometric indicators and using the ISI Web of Science information.
Method ! A bibliometric evaluation of the evolution of scientific production in the field of lung transplants between 1989 and 2009 was conducted. The ISI Web of Science database was searched to retrieve articles on lung transplantation published over a period of two decades . A search using the keywords "lung transplant*" OR "pulmonary transplant*" yielded a total of 11 041 publications, of which 6409 were articles. Two more keywords, using the Pubmed browser of Medical Subject Headings (MeSH), were included to ensure the accuracy of our keyword search. After the keyword "lung graft*" was added to the search terms, the result yielded a total of 11 127 publications, including 6453 articles and after adding "lung graft*" OR "pulmonary graft*", the result was 11 170 publications, of which 6472 were articles. Therefore, as graft did not appear as a common term in scientific publications, the final search terms selected were "lung transplant*" OR "pulmonary transplant*". The search was only performed on article-type documents, reflecting the achievements in the field of lung transplants. The specific features including year of publication, language of the article, geographical distribution, first author, main journal publishing these articles, journals publishing highly cited articles, and institutional affiliation were analyzed. In addition, the citation and characteristics of the most cited articles each year and over the total period were evaluated. The citation characteristics of articles were additionally analyzed. The analyzed timespan of the citations covers all citations from 1990 to July 2010. The top 10 countries based on citation per year and citation per paper were identified. Descriptive statistics were used to analyze the data, and calculations were done using Microsoft Excel ® software (version 2007, Microsoft Corp., Redmond, WA, USA).

Number of publications: trend between 1989 and 2009
Time-trend of the number of articles published between 1989 and 2009 is shown in l " Fig. 1. There was a total 579 indexed articles in 2009, compared to 85 in 1989, which amounts to a more than 6.81-fold increase between 1989 and 2009. There was a sudden increase in the numbers of articles between the years 1990-1992, 1995-1996 and 2003-2004; especially since 2006, an accelerated growth in the number of articles was notable. l " Fig. 2 shows the time-trend of the number of articles published for the four countries who contributed most, namely the US, the UK, Germany and Canada. This time-trend reflects the increasing trend in the number of articles in most contributing countries, all of which show a similar pattern.

Geographical distribution
A total of 45 countries contributed to advances in the field of lung transplantation by publishing articles. With a total of 3237 articles, North American countries contributed 50.4 % of all published articles. Twenty-two countries from Europe contributed  Of all countries involved, the USA contributed the greatest number of articles on pulmonary transplants with 2798 articles (43.6 %), followed by England with 587 articles (9.1 %), Germany with 554 articles (8.6 %), Canada with 424 (6.6%), and France with 399 articles (6.2 %). Australia, Italy, Switzerland and Netherlands, each with less than 5% of the total number of articles, were some of the other contributing countries (l " Table 1).  Table 2). l " Table 3 lists the journals publishing the most highly cited articles (more than 100 citations). Thus "Journal of Heart and Lung Transplantation" with 25 highly cited articles ranked first, fol-   lowed by "Chest" and "Circulation" with 9 and 7 articles, respectively.

Citation profile of articles
When we looked at the number of citations per highly cited papers, "New England Journal of Medicine" with 6 highly cited articles had 407 citations per article and ranked first. "Journal of the American College of Cardiology" with one article and 356 citations per article and "American Journal of Medicine" with one article and 337 citations per article ranked 2nd and 3rd, respectively (l " Table 3).

Citation and characteristics of top cited papers on lung transplantation
A review of the top cited articles including article title, first author affiliation, name of the publishing journal and citation number of each article between 1989 and 2009 is shown in l " Table 4, and reflects the change in pattern and subject of the most cited articles.

Profiles of authors and institutions
The top ten authors with the maximum number of articles published in the field of lung transplantation are shown in l " Table 5. G. A. Patterson from Washington University with a total of 129 articles, E. P. Trulock from Washington University with 101 articles and J. Wallwork from Cambridge University with 98 articles were the authors with the greatest number of articles to their name in this field.
l " Table 5 shows the top ten institutions with the greatest number of articles. Washington University with 259 articles (4.0 %) published the most publications, followed by the University of Pittsburgh with 250 articles (3.9 %), and the University of Toronto with 184 (2.9 %) articles. The US National Institutes of Health (NIH) was the major funding agency for research in this field, funding 35 studies. The Health Resources and Services Administration and the Canadian Institutes of Health Research were other major funding agencies for research in this field, and funded 11 and 9 studies, respectively (l " Table 5).

Article profiles
The language of most articles was English (94 %, n = 6024), followed by German (2.3 %, n = 145), French (2.0 %, n = 128), and Spanish (1.0 %, n = 70). Among the journals publishing articles in the field of lung transplantation, "Journal of Heart and Lung Transplantation" alone published 19.9 % of the total number of articles in the field of lung transplantation, followed by "Transplantation" with 435 (6.8 %) total articles, "Chest" with 329 (5.1 %), "Annals of Thoracic Surgery" with 269 (4.2 %), "American Journal of Respiratory and Critical Care Medicine" with 218 (3.4 %) and "Journal of Thoracic and Cardiovascular Surgery" with 209 (3.2 %) articles. Most articles were published in professional journals in this field, with no journal focusing more on general medical topics found among the top 10 journals (l " Table 6). Discussion ! Lung transplantation, a medical achievement which has prolonged the life and improved the quality of life of patients with severe pulmonary disease, has increasingly attracted the attention of medical professionals. This is the first study which has evaluated the increasing emergence of publications in the field of lung transplantation. The result of our study showed a rapid growth in the number of publications in this field (681 %) in the last two decades, especially since 2006. The pattern of this growth is similar for most contributing countries in this field. As regards to the geographical distribution of contributing regions, North America countries (50.4 %) and European countries (46.0%) contributed nearly 90 % of scientific articles in this field. African countries contributed the least. As shown in previous studies [20][21][22][23], the USA and its institutions were foremost among the contributing countries with regard to publications, followed by the UK and Germany. Not only was the USA the most important country contributing published articles but US institutions were the major funding source for research in this field. One interesting finding of this study was that articles from Canada had the maximum number of citations per paper; however when looking at the number of articles published, Canada only came fourth. This study found that only 6.0 % of articles in this field were written in languages other than English. This is not only due to the widespread use of English as the language of science but may be a result of the fact that most journals, especially those indexed by ISI, are published in English. An analysis of the journals which published the most articles in this field showed a preference for articles to be published in professional journals focusing on transplantation or heart and lung surgery. This study showed that the number of citations of articles increased from 1989-2009 around 399.5-fold, indicating the increasing interest of the medical world in this topic, while citations per paper decreased during the same period by a factor of 15.3. This was due to the long timespan of this study (from 1990 to July 2010), which meant that older papers had more citations and newer ones had fewer ones, simply because older articles were available for a longer period, which reflects the influence of time on citation rates. The average number of citations per paper and the low proportion of uncited papers (12 %) reflected the fact that articles in this field attract more attention compared to other fields of medicine. Hamiltonsʼ studies, using data from the ISI, stated that approximately 46% of papers in medicine remain uncited 5 years after publication [24,25]; however this may be an overestimation because Hamiltonsʼ statistics included different types of publications. The number of publications on and the scientific interest in the field of lung transplant has increased dramatically in recent years. The citations of articles on lung transplants are increasing and the number of uncited articles has dropped compared to the average citation of articles and uncited articles in the field of medicine.