Marie-Claire Busnel

Fetal responses to acoustic stimulation depend on heart rate variability pattern, stimulus intensity and repetition.

Fetuses (37-40 wks DA) were exposed to three successive presentations of a 5-s high-pass filtered (800 Hz) pink noise either at 105 dB or at 110 dB SPL. Stimulations were given during high or low variability heart rate (HR) patterns (HV or LV) which presumably correspond mostly to active and quiet sleep episodes, respectively. The proportion of fetuses showing cardiac response (CR) was always greater than the proportion showing leg movement (LM) but the presence of an accompanying leg movement always increased the amplitude of CR, independent of HR pattern, stimulus repetition and intensity. Fetal reactiveness always diminished with stimulus repetition but diminished more on the three examined dimensions (CR ratio, LM ratio and CR amplitude) with LV infants than with HV infants, and more with the 105 dB stimulus than with the 110 dB stimulus. More importantly, stimulus parameters and HR patterns interacted. At 110 dB in HV, neither the median amplitude of the CRs nor the probability of a CR changed over trials but the probability of a concommittant LM decreased. At 110 dB in LV, repetition induced a decrement on all three response dimensions from the second trial onwards. At 105 dB in HV, LM decreased rapidly, as much as at 110 dB in LV. Thus, state, as reflected by HR pattern, plays a significant role in determining the occurrence and the amplitude of the CR and the occurrence of a LM which, in turn, will enhance the CR amplitude.

Feasibility of Prenatal Hearing Test

Variability in foetal responses to sound stimulations is described and the effect of the different factors involved in this reactivity, in particular the physical characteristics of the stimulus and state of alertness of the foetus, is discussed. Results obtained with a high pass filtered pink noise at a 106, 109 and 113 dB SPL on 37-40 week foetuses are given to illustrate this dependency. For all tested levels, responsiveness was reduced after repetition of the stimulus. This was observed even at 113 dB when stimulation was preceded by a series of lower level stimuli to which foetuses were (or became) unresponsive. Motor responses (lower limb movements) were the first and the most affected by stimulus repetition, followed by cardiac response decrement--but with a lower proportion of non-responses, especially at 113 dB. Consequently, with this specific stimulus, cardiac reactivity seems a more reliable parameter to examine when more than one stimulus is needed to ascertain foetal hearing. It was also demonstrated that foetuses were much less reactive when stimulated during low heart rate variability sequences than during high heart rate variability. Testing of prenatal hearing seems feasible in utero and should be a promising method for detecting gross hearing impairment once the influence of each biophysical parameter has been carefully studied.

Fetal cardiac and motor responses to octave-band noises as a function of central frequency, intensity and heart rate variability.

Accelerative and decelerative cardiac responses and motor responses (leg movements) of 37-40 weeks (G.A.) fetuses are analyzed as a function of the frequency of three octave-band noises (respectively centered at 500 Hz, 2000 Hz and 5000 Hz) and of their intensity level (100, 105, 110 dB SPL, ex utero), during high (HV) and low (LV) heart rate (HR) variability pattern states. In both states, increasing the frequency and/or the intensity of the acoustic stimulation: (i) increases the ratios and amplitudes of accelerations, and the motor response ratios, (ii) reduces deceleration ratios and motor response latencies. Cardiac and motor reactiveness are higher in HV than in LV with acceleration ratios always greater than motor ones. However, when a high intensity and/or frequency is used, the reactiveness differences between states disappears. Low intensity and/or frequency stimulation levels induce a majority of decelerations.

Decelerative cardiac responsiveness to acoustical stimulation in the near term fetus

Human fetal cardiac responses (36–39 weeks gestational age) to brief, repeated vocal stimuli (male or female voice uttering the same sentence), given at 90–95 dB SPL ex utero (around 20–30 dB less in utero) during a state of low fetal heart rate (FHR) variability, were examined using highly conservative statistical criteria taking into account each subjects prestimulus FHR variability. Subjects exposed to either of the two stimuli displayed significantly more decelerative heart rate (HR) changes compared to control subjects receiving no stimulation. The decelerative changes started during the first seconds following the onset of stimulation and reached their amplitude peak within 10 or 20 sec, depending on the subject. The directions—HR acceleration or deceleration—and the amplitude of the response depended on prestimulus HR variability only, not on prestimulus level. No major difference was found between the effects of the two voices. The data are compared to previous studies demonstrating fetal decelerative changes to acoustic stimuli of less than 105 dB SPL. The choice of an objective criterion to define an HR response and the possible orienting response nature of the decelerative change are discussed.

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 attenuated in a complex manner as frequency increases. The present work investigated whether a plain rubber sphere which was filled with water could be considered as a reliable nonbiological model in a study describing the characteristics of sound transmission. A sweeping pure tone, presented externally, was measured inside the rubber sphere using a high signal-to-noise ratio experimental hydrophone. A paradigmatic three components curve was observed between 100 and 20,000 Hz. In the first component of the curve (low to midfrequencies between 100 and 1,000 Hz), the intensity of the inside signal remained stable. The second component of the curve was composed of higher frequencies with the inside pressure falling gradually, demonstrating attenuation of the external signal. The third component of the curve appeared above a critical frequency, the value of which depended on several model and environment parameters. In this component, a series of rapid peaks and drops of the inside high frequency pressure was observed, indicating the presence of resonance systems. Analyses were carried out on the effects of several acoustical parameters, including: the size of the sphere, the location of the hydrophone in the sphere, the distance between the signal source and the hydrophone, the location of the external reference microphone, and the acoustical structure of the environment. These parameters allowed for the definition of their respective roles in the in-utero transmission of external sounds. These data were then compared with measurements performed within a biological model--ewes--under close acoustical settings. The comparisons confirmed the validity of the measurements, suggesting that the model may be useful in studies of sound transmission in utero.

And What of Fetal Audition

The question of whether the fetus (or even for certain sensory modes, newborn) sees, hears, tastes and feels, has been under discussion for many years, but only recently has actual experimentation on the subject been carried out.

Ultradian and circadian respiratory rhythms in grouped small laboratory vertebrate species as a method to assess the effects of environmental challenges

The recording over several days of the respiratory gases of groups of different laboratory vertebrates (mice, rats, quails), placed in a chamber with controlled ventilation, and in standardized environmental conditions of temperature, humidity, light, noise and feeding, shows ultradian (tau less than 24 hr) and circadian (tau congruent to 24 hr) rhythms. A simple variance analysis method shows periodic carbon dioxide changes, due to different environmental stimuli. Societal, light, acoustical, carbon monoxide and starvation challenges are given as examples. This technique enables us quickly to collect, on a great number of animals, data which correspond to societal behavior changes peculiar to the considered species.

Respiratory behavior in groups of deaf and non-deaf GFF male mice.

Carbon dioxide emission (VCO2) of groups of 10 GFF mice, genetically deaf and non-deaf, were compared, in controlled conditions of temperature 20-21 degrees C, humidity 50-80% and light (LD12:12; L = 108 lux). A circadian rhythm of VCO2 was evidenced in both genotypes, with levels in D and in L significantly (0.001 less than p less than 0.01) greater in deaf than in non-deaf mice. Photic VCO2 variations were significantly (0.001 less than p less than 0.05) smaller at L----D and D----L in the deaf than in non-deaf genotype. Ultradian (tau greater than 20 minutes) rhythms were evidenced in both genotypes; Fourier periodic analysis showed several significant (0.001 less than p less than 0.05) differences between these 2 genotypes concerning mainly amplitudes, whilst spectral analysis showed slight frequency differences between them. Survival to an acute nitrogen hypoxia or to an acute carbon monoxide intoxication which was significantly (p less than 0.001 and p less than 0.05) lower in deaf than in non-deaf individuals confirms the differences in respiratory behavior of groups of these two strains of mice.

Chronobiological variations in the effects of acoustical stimuli on carbon dioxide emission of light‐dark synchronized grouped male mice

Abstract A continuous recording of carbon dioxide emission (VCO2) was used to quantify the respiratory responses of grouped male GFF mice, LD12:12 synchronized and submitted to one hour of acoustic stimulation. It was shown that, both in percentage and amplitude of VCO2 variations, the highest and most frequent responses were: (1) during the dark (D) when mice are more active, (2) at the beginning of stimulation vs. at the end. Moreover, ultradian respiratory variations of the groups influence the number of the responses to the acoustical stimuli.

Stimulations acoustiques au cours du développement du système auditif et adaptation au bruit chez la souris

To assess the effects of an acoustically enriched environment during the auditory system development, groups of mouse pups, from two strains (Swiss Albinos Rb-3 and deafness, the latter carrying a recessive gene [dn] making homozygous dn/dn totally deaf), were exposed to pulsed pure-tone stimulation (2500 Hz; 85 ± 5 dB SPL) at different periods of development from conception to weaning. Growth curve, weight at 40 days, eye opening and behaviour at 24 days to the same stimulus were analyzed as a function of the mothers audition (hearing or deaf) and of the period of acoustic exposure: exposed since conception, since birth or from 9 days (date of onset of audition).Eye opening is more precocious in all three experimental groups than in controls.Contrary to mouse pups exposed from 9 days, those (also from deaf mothers) treated before onset of hearing show normal growth and behavioural indifference to the stimulus at 24 days. The significant lack of physiological and behavioural effect of the sound stimulus ...