Abundant clinical evidence shows that sounds produced outside the uterus can be sensed by the fetus resulting at times in movements, heart rate acceleration, and disruption of behavioral state. Acoustic signals that comprise the fetal sound environment include those produced endogenously (e.g., maternal voice) and exogenously (e.g., industrial noises). Thus, two important issues need to be addressed. First, concerns about the long-term effects of environmental stimuli on the fetus have been raised by perinatologists who test for fetal response to acoustic stimulation and by occupational health specialists and employers who recognize the potential, yet undocumented, fetal hazards in the noisy workplace. No guidelines or consensus standards have been developed specifically for pregnant women working in sound and vibration-rich occupations. Second, prenatal experiences with speech sounds may contribute to the development of mechanisms for phonetic identification and discrimination, a process known as pre-programming. This theory is dependent upon an understanding of the elements of speech to which the fetus may be privy. The long- term objectives of the present application are to determine the characteristics of the sound and vibration environment in utero and the effects of these stimuli on the fetus. Preliminary research has revealed that mechanical vibration provides an efficient means of delivering energy to the uterus. Moreover, entirely different sound pressure level profiles are found within the uterus when vibratory energy is applied directly to the abdomen in contrast to sound energy which reaches the abdomen through an air-borne route. We now propose to extend these observations by analysis of the efficiency of the energy transfer from surface vibrators to the fetus, especially in the range of fetal resonance frequencies, as measured with accelerometers. In addition, we plan to study the intelligibility of speech sounds recorded with a hydrophone in the human uterus at the time of delivery. Spectral analysis of the fetal electrocorticogram will be made to determine how fetal behavioral state is altered by sounds and vibrations of differing frequencies and durations. Fetal cerebral blood flow will be measured to determine the effects of amplitude and bandwidth stimulation along the fetal auditory pathway. Fetal brainstem auditory evoked responses will provide a quantitation of decreases in fetal hearing sensitivity resulting from maternal high intensity noise exposure. Finally, the isolation of the fetus from sounds produced outside the mother will be assessed. Observations of the characteristics and effects of sound, vibration and speech are expected to provide bases for assessing the usefulness and safety of the Vibroacoustic Stimulation Test, for understanding fetal exposure in the workplace and evaluating what the fetus may be hearing.
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