WHAT SOUNDS REACH FETUSES - BIOLOGICAL AND NONBIOLOGICAL MODELING OF THE TRANSMISSION OF PURE-TONES

In utero transmission of external and maternal sounds has been studied in pregnant women and in an animal model of human species, the sheep. These works, especially the most recent ones, suggest that local and environmental factors interfere in such a way that signals are attenua ted in a complex manner as frequency increases. The present work inves tigated whether a plain rubber sphere which was filled with water coul d be considered as a reliable nonbiological model in a study describin g the characteristics of sound transmission. A sweeping pure tone, pre sented externally, was measured inside the rubber sphere using a high signal-to-noise ratio experimental hydrophone. A paradigmatic three co mponents curve was observed between 100 and 20,000 Nz. In the first co mponent of the curve (low to midfrequencies between 100 and 1,000 Hz), the intensity of the inside signal remained stable. The second compon ent of the curve was composed of higher frequencies with the inside pr essure falling gradually, demonstrating attenuation of the external si gnal. The third component of the curve appeared above a critical frequ ency, the value of which depended on several model and environment par ameters. In this component, a series of rapid peaks and drops of the i nside high frequency pressure was observed, indicating the presence of resonance systems. Analyses were carried out on the effects of severa l acoustical parameters, including: the size of the sphere, the locati on of the hydrophone in the sphere, the distance between the signal so urce and the hydrophone, the location of the external reference microp hone, and the acoustical structure of the environment. These parameter s allowed for the definition of their respective roles in the in-utero transmission of external sounds. These data were then compared with m easurements performed within a biological model-ewes-under close acous tical settings. The comparisons confirmed the validity of the measurem ents, suggesting that the model may be useful in studies of sound tran smission in utero. (C) 1998 John Wiley cli Sons, Inc.