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Auditory perception of ultrasound in patients with sensorineural and conductive hearing loss

THE normal frequency range of human hearing for air-conducted sounds extends from approximately 10 Hz to 20 kHz. A few subjects can hear even higher pitched sounds of up to 26 kHz, and these individuals may even hear dog whistles. Sounds with frequencies above the normal human auditory range are known as ultrasound. A fact not well known is that ultrasound can plainly be heard by normal man if it is delivered by bone conduction. Deatherage and his cojleagues (1956) reported that they could hear a high-pitched tone while they were working under water in the beam of a transducer transmitting at 50 kHz. Bone-conducted ultrasound is heard as a high-pitched squeak (Gavreau, 1948) and, as the frequency alters from 165 kHz to 120 kHz, no subjective change in frequency is noted. Pumphrey (1950) has concluded that as the basal end of the cochlea can clearly respond to sounds of up to 100 kHz, the failure to hear ultrasound by air-conduction must be related to a failure of the middle-ear mechanism to cope with these frequencies. Sagalovich and Melkumova (1964) have investigated the bone-conduction mechanism concerned with ultrasound. They performed some experiments using dried skull bones and found that the human temporal bone could convey sounds with frequencies up to 440 kHz. The optimum conduction through the skull bones occurred using frequencies between 60 kHz and 100 kHz; ultrasounds of higher or lower frequency were conducted less well. They also showed that ultrasound conducts to the promontory more easily when the transducer is placed on the temporal bone rather than on any other part of the skull. Kietz (1951) has suggested that patients with sensorineural hearing loss can be separated into two groups according to the results of testing with ultrasound. Using ultrasound at 32 kHz at a fixed intensity, he noted that some patients heard nothing while others heard a high pitched squeak. Bellucci and Schneider (1962) reported that patients with no residual cochlear or vestibular function (total deafness) could not hear ultrasound of 62-5 kHz. Sagalovich and Pokryvalova (1966) noted normal perception of ultrasound in patients with otosclerosis but raised ultrasound thresholds in patients with sensorineaural hearing losses. The report which follows concerns a clinical study of ultrasound. The