title: The effects of pressure on arthritic knees in a rat model of CFA-induced arthritis.
abstract: BACKGROUND
  Pain is influenced by weather changes under certain circumstances, and inflammatory pain in animal models is ameliorated by pressure, but the underlying mechanism of atmospheric pressure has not been clearly elucidated.
  
  
  OBJECTIVE
  To examine the effect of pressure on pain in an arthritic animal model.
  
  
  METHODS
  Controlled animal study.
  
  
  METHODS
  Laboratory animal study.
  
  
  METHODS
  Following an injection of complete Freund's adjuvant (CFA) into one side of a knee joint, 32 rats were assigned randomly to 2 groups and either placed under 1 or 2.5 atmospheres absolute (ATA) in a hyperbaric chamber for 5 hours. The pain levels were assessed daily for up to 2 weeks post-injection to determine the changes in weight bearing (WB) of the affected limbs. In addition, the levels of gelatinase, MMP-2, and MMP-9 expression in the synovial fluids of the knees were analyzed.
  
  
  RESULTS
  After arthritis induction, the rats in the 1 ATA group showed reduced WB of the affected limbs (< 10% of normal limbs). This reduction in WB peaked at 2 days after the injection and then decreased spontaneously. Nevertheless, the pain behavior lasted for more than 2 weeks. In the 2.5 ATA group, the WB was significantly better during the experiment.  The MMP-9/MMP-2 ratio increased at 7 and 14 days after the CFA injection in the 1 ATA group. However, repetitive exposure to 2.5 ATA significantly reduced this ratio in the 2.5 ATA group.
  
  
  CONCLUSIONS
  Although a sufficient number of samples were used to support the hypothesis that high atmospheric pressure improves a painful condition in this study, an additional larger-scale study will be needed to confirm these findings.
  
  
  CONCLUSIONS
  Exposure to elevated pressures appears to relieve arthritic pain for extended periods by reducing the inflammatory process and should be considered as a possible alternative pain-reducing therapy.
authors.affiliation: Pusan National University School of Medicine, Pusan, Korea.
authors.forename: Sung Tae
authors.initials: ST
authors.lastname: Koo
authors.forename: Chang-Hyung
authors.initials: CH
authors.lastname: Lee
authors.forename: Hyeunseok
authors.initials: H
authors.lastname: Choi
authors.forename: Yong Il
authors.initials: YI
authors.lastname: Shin
authors.forename: Ki Tae
authors.initials: KT
authors.lastname: Ha
authors.forename: Hanna
authors.initials: H
authors.lastname: Ye
authors.forename: Hyun Bo
authors.initials: HB
authors.lastname: Shim
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy; D001274:Atmospheric Pressure; D006931:Hyperbaric Oxygenation; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000032:analysis / Q000096:biosynthesis; D020780:Matrix Metalloproteinase 9 / Q000032:analysis / Q000096:biosynthesis; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy*; D010146:Pain / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013582:Synovial Fluid / Q000737:chemistry; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9