The concentration of thiobarbituric acid reactive substances (TBARSs) in plasma and erythrocytes, the activity of selected antioxidant enzymes in erythrocytes: catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), and the levels of hemoglobin (HGB) and haematocrit (HCT) were determined in 40 patients with sudden sensorineural hearing loss (SSNHL) subjected to 14 treatment sessions in a Haux Starmed 2200 hyperbaric chamber. Hyperbaric oxygen (HBO) therapy involved breathing 100% oxygen at 0.25 MPa. Blood for analysis was collected from the basilic vein at three time points: before the first HBO session, approximately 5 min after the first session, and after the 14th session. The control group included 20 healthy individuals never before treated with HBO therapy. Compared to the pre-HBO values, a 10% increase (P < 0.05) in the TBARS concentration in erythrocytes, a 28% increase in the GPx activity (P < 0.05), and a 7% decrease in the SOD activity (P < 0.05) were observed after 14 HBO sessions. The CAT activity decreased by 6% (P < 0.05) after the first session. The TBARS concentration in plasma was 13% higher (P < 0.01), while that in erythrocytes was 24% lower (P < 0.001) in the SSNHL patients before the first HBO session compared to the control group. The CAT activity in the SSNHL patients before HBO therapy was 26% higher (P < 0.001) than that in the control group. A statistically significant reduction in HGB and HCT after 14 HBO sessions (P < 0.01) compared to the pre-HBO values was demonstrated. SSNHL is accompanied by disturbance in the oxidant-antioxidant equilibrium. Repeated stimulation with hyperbaric oxygen modulates the activity of antioxidant enzymes. It seems that the increased generation of hydrogen peroxide is responsible for the changes in the activity of antioxidant barrier enzymes observed after HBO sessions.
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