Acoustic measurements of objective tinnitus

Ear canal sound pressure levels were measured from a 38-year-old woman who had experienced objective tinnitus in her right ear for approximately 2 years. The tinnitus sounded like a series of "sighs" that were synchronous with her pulse rate. Because the level of the tinnitus fluctuated in a pulsing manner, it appeared to be of vascular origin. Psychoacoustically, the tinnitus behaved like a low-pass masker (cutoff frequency = 1.5 kHz) of about 40 dB SPL. This masking effect was manifested as a low-frequency hearing loss in the subject's right ear. A miniature microphone system was used to monitor the tinnitus before, during, and after a jugular-vein ligation. Because the cause of the tinnitus was only generally known, acoustically monitoring the sound as the jugular vein and/or its tributaries were systematically clamped and then released enabled the site of generation to be known exactly. By monitoring the tinnitus during surgery, the effectiveness of the corrective procedure could be immediately evaluated. Hearing sensitivity in the affected ear returned to normal limits following the elimination of the tinnitus. One year after the surgery, the tinnitus was barely audible to the woman, but only when she positioned her head a specific way. The level of the tinnitus measured in this head-turned condition was markedly lower than the level obtained preoperatively.