Fetal acoustic stimulation test: stimulus features of three artificial larynges recorded in sheep.

Abstract

The purpose of the current study was to evaluate the characteristics of vibroacoustic devices used for fetal stimulation. Intrauterine sound pressure levels over a frequency range of 40 to 5000 Hz were measured with hydrophones in anesthetized sheep. Stimulators included the AT&T (Martinsburg, W.V.) and Servox (Hearing Instruments, Piscataway, N.J.) artificial larynges, the Corometrics fetal acoustic stimulator (Wallingford, Conn.) and electric toothbrush. Intrauterine spectral patterns resulting from stimulation with the AT&T, Servox, and Corometrics devices were characterized by numerous high-level overtones above a fundamental frequency between 97 and 163 Hz. Fundamental frequencies recorded during toothbrush stimulation were 22 to 24 Hz with reduced but identifiable overtones up to 250 Hz. Fetal vibroacoustic stimulators that operate on the principle of the electronic artificial larynx produce very similar intrauterine sound pressure levels.