Acquiring the optimal time for hyperbaric therapy in the rat model of CFA induced arthritis.

BACKGROUND We previously published an article about the pressure effect using a rheumatoid animal model. Hyperbaric therapy appears to be beneficial in treating rheumatoid arthritis (RA) by reducing the inflammatory process in an animal model. In this sense, acquiring the optimal pressure-treatment time parameter for RA is important and no optimal hyperbaric therapy time has been suggested up to now. OBJECTIVE The purpose of our study was to acquire the optimal time for hyperbaric therapy in the RA rat model. STUDY DESIGN Controlled animal study. METHODS Following injection of complete Freund's adjuvant (CFA) into one side of the knee joint, 32 rats were randomly assigned to 3 different time groups (1, 3, 5 hours a day) under 1.5 atmospheres absolute (ATA) hyperbaric chamber for 12 days. The pain levels were assessed daily for 2 weeks by weight bearing force (WBF) of the affected limb. In addition, the levels of gelatinase, MMP-2, and MMP-9 expression in the synovial fluids of the knees were analyzed. RESULTS The reduction of WBF was high at 2 days after injection and then it was spontaneously increased up to 14 days in all 3 groups. There were significant differences of WBF between 5 hours and control during the third through twelfth days, between 3 hours and control during the third through fifth and tenth through twelfth days, and between 3 hours and 5 hours during the third through seventh days (P < 0.05). The MMP-9/MMP-2 ratio increased at 14 days after the CFA injection in all groups compared to the initial findings, however, the 3 hour group showed a smaller MMP-9/MMP-2 ratio than the control group. LIMITATION Although enough samples were used for the study to support our hypothesis, more samples will be needed to raise the validity and reliability. CONCLUSION The effect of hyperbaric treatment appears to be dependent upon the elevated therapy time under 1.5 ATA pressure for a short period of time; however, the long-term effects were similar in all pressure groups. Further study will be needed to acquire the optimal pressure-treatment parameter relationship in various conditions for clinical application.