Table 6.

The top 20 most frequently occurring keywords.

Rank	Keyword	Occurrences	Centrality	Rank	Keyword	Occurrences	Centrality
1	Bronchiolitis obliterans syndrome	1587	1.52	11	Bone marrow transplantation	269	0.18
2	Bronchiolitis obliteran	1167	0.29	12	Rejection	242	0.48
3	Lung transplantation	1128	0.45	13	Diagnosis	236	0.38
4	Recipient	476	0.17	14	Survival	227	0
5	Risk factor	452	1.22	15	Chronic rejection	207	0.54
6	Disease	372	0.38	16	Expression	176	0.12
7	International society	300	0.54	17	Allograft rejection	164	0.29
8	Obliterative bronchioliti	284	0.12	18	Cystic fibrosis	163	0
9	Vs host disease	276	0	19	Lung transplant	144	0
10	Heart	269	0.29	20	Chronic lung allograft dysfunction	139	0.06