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11:15

2PA12. Catalase and cystearaine inhibit indirect sonochemical effects of caritation on cellular DNA. D. L. Miller, R. M. Thomas, and M. E. Frazier (Biol. and Chem. Dept., Battelle PNL, P.O. Box 999, Richland, WA 99352)

Ultrasonic cavilation can indirectly cause cellular bioeffects due to the production of toxic sonochemicals. Phosphate buffered salinę (PBS) was exposed to 1.61-MHz ultrasonic cavitation at 20 *C in a rotating-tube exposure system to build up sonochemical products. Single strand DNA breaks (SSBs) were tlien induccd by trcating Chinese hamster ovary (CHO) cells with the cavitated PBS for 30 min on ice. This indirect effect could be explained by the action of cavitation-gcnerated hydrogcn peroxide (e.g., up to 16 /im after 30-min exposure) in the PBS. Adding catalasc to the cavitatcd PBS before celi treatment elimi-nated the effect. Tests with hydrogen pcroxide sliowed that 16 /zm H₂0₂ treatment for 30 min on ice was as cffective as 1 Gy of gamma rays in producing SSBs. The SSB effect of H₂0₂ was reduced by addition of the radical scavenger cysteamine to the cells before treatment. These results indicate that DNA effects from ultrasonic cavitation can occur indirectly without the highly destructive direct interaction of cells and cav-ities. [Supported by PHS Grant CA42947 awarded by the National Institutes of Health.]

TUESDAY MORNING, 30 APRIL 1991

INTERNATIONAL C, 9:00 TO 11:30 A.M.

Session 2PP

Psychological and Physiologjcal Acoustics: Models and Mechanisms of the Auditory Periphery

Bradford D. May, Chair

Department of Otolaryngolog—HNS, Johns Hopkins Uniuersity School of Medicine, Baltimore, Maryland 21204

Contrihuted Papers

9K)0

2PP1. Sound intensity and reflection coefficient measurements in the ear canal. R. D. Rabbitt and J. Dragicevie (Depart. of Mech. Eng., Washington Univ., St. Louis, MO)

The sound power per unit cross-sectional area (specific power) is mcasured in the ear canal using a three-probe-microphone system. Pres-sure measurements recorded from locations within the core region of the ear canal are utilized to determine the instantaneous intensity of sound waves traveling in the lengthwise direction. A direct time-domain method provides the specific power contained in waves traveling through the region of the canal containing the microphones. The time average of the instantaneous intensity defines the specific power ab-sorbed by the ear. Furthermore, the time average of the positive part of the intensity determines the incident specific power, or input to the ear, and the time average of the ncgative part of the intensity determines the reflected, or emitted, specific power. Signal averaged data are collectcd for pure-tone sweeps from 4 to 15 kHz. [Work supported, in part, by the Whitaker Foundation and the National Science Foundation ]

9:15

2PP2. Pressure transfer function from the diffuse field to the human infant ear canal. Douglas H. Keefc, Edward M. Burns, Jay C. Bulen, and Shari L. Campbell (School of Musie, DN-10, and Dept. of Speech and Hcaring Sci., JG-15, Univ. of Washington, Seattle, WA 98195)

The diffuse field pressure transfer function //(/) to the ear canal of human infants was mcasured from 100-11 000 Hz. The diffuse field pressure and the ear canal pressure were simultaneously mcasured in a reverberant room using spatial averaging of source and microphones.

The probe microphone tip was inserted 5 mm into the infant ear canal, and the parent was instructed to hołd the infant while slowly walking around the room; an experimcnter walked around the room with the other microphone. Results using KEMAR and in adult canals were consistent with the literaturę. //(/) for the 1-month-old infants has a strong pcak (10-15 dB) at 4-5 kHz. The majority of the ten infants showed a twin peak structure, with the additional peak (8-12 dB) at 5-6 kHz. //(/) has a dip at 8-9 kHz and inereases up to 11 kHz. A 5-dB peak at 1-2 kHz may be due to the proximity of the parent*s torso to the infant's head. Additional results on older infants will be dis-cussed. [Work supported by NIH.]

9:30

2PP3. A physical model for the middle ear carity (MEC). Sunil Puria (AT&T Bell Labs, 600 Mountain Ave., Murray Hill, NJ 07974 and The City College of CUNY, New York, NY 10036)

The input impcdance of the cat MEC is modeled by approwmating łhe bulla and tympanic cavitics as a Cascade of two cytindrical lubes. The smali hole in the bony septum, known as the foramen, is approxi-mated as a short cytindrical tubę. Nonplanar wave propagation, due to the foramen, and visćo-thermal losses at the cavity walls are included in the model. The model was verified by making impcdance measurements on cylindrical cavities for frequencies up to 12 kHz. The intact case, as well as the open bulla case and plugged foramen case, is simulated and shown to be in good agreement with animal measurements [T. J. Lynch, III, Ph.D. thesis, MIT (1981)]. In addition to the bulla resonance near 4.5 kHz, the model predicts that there is a second bulla resonance near 26 kHz. Without the bony septum, the resonances are shown to be near 10 and 20 kHz. It is hypothesized that the role of the foramen is to shift the resonant freąuencies.

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J. Acoust. Soc. Am., Vol. 89, No. 4, Pt 2, April 1991

121st Meeting: Acoustical Society of America

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