Successful treatment of noise-induced cochlear ischemia, hypoxia, and hearing loss

Cochlear blood flow (CoBF), perilymphatic partial pressure of oxygen (PL-pO(2)), cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs), and auditory brainstem responses (ABRs) were studied in noise-exposed guinea pigs during and after the following treatments: intravenous infusion of isotonic saline (placebo); blood flow promoting drugs (hydroxyethyl starch = HES, pentoxifylline, betahistine, gingko biloba, naftidrofuryl); antiinflammatory agents (prednisolone, diclofenac sodium, histamine Hi-receptor antagonist); isobaric oxygenation (IBO); and hyperbaric oxygenation (HBO) with and without supplements (simultaneous infusion of isotonic saline, pentoxifylline, prednisolone, or HES). It was found that PL-pO(2) declined simultaneously with deterioration of CM, CAP, and ABR amplitudes after exposure to broad-band noise (bandwidth 1-12 kHz, 30 min, 106-dB SPL). CoBF decreased only 30 min after cessation of broad-band noise and progressed with cochlear hypoxia, while the hearing loss showed no further signs of deterioration and no recovery up to 3 h after exposure. Treatment (60 min) started 60 min after cessation of noise and was studied for a further 60 min. Isotonic saline did not influence the measuring parameters. Noise-induced cochlear hypoxia was compensated by IBO and more effectively by HBO with and without supplements, while other treatments had no sustained effect. A sustained therapeutic effect on noise-induced cochlear ischemia was achieved only by HES, HBO+HES, and pentoxifylline. However, the best therapeutic effect on noise-induced hearing loss was achieved with a combination of HBO and prednisolone, followed by monotherapy with prednisolone or RES with the result that not only did the CAPs and ABRs completely recover, the CMs also showed significant improvement, although full recovery did not occur. All other therapies were significantly less effective or did not improve noise-induced reduction of auditory evoked potentials.