Evaluation of fetal exposure to environmental noise using a computer-generated model

Abstract

Acoustic noise can have profound effects on wellbeing, impacting the health of the pregnant mother and the development of the fetus. Mounting evidence suggests neural memory traces are formed by auditory learning in utero. A better understanding of the fetal auditory environment is therefore critical to avoid exposure to damaging noise levels. Using anatomical data from MRI scans (N = 3), we used a computational model to quantify the acoustic field inside the pregnant maternal abdomen. We obtained acoustic transfer characteristics across the human audio range and pressure maps in transverse planes passing through the uterus at 5 kHz, 10 kHz and 20 kHz, showcasing multiple scattering and modal patterns. Our calculations suggest that for all datasets, the sound transmitted in utero is attenuated by as little as 6 dB below 1 kHz, confirming results from animal studies that the maternal abdomen and pelvis do not shelter the fetus from external noise.

Keywords: Computational Acoustics; Fetal auditory system; Fetal ear; Fetal sound exposure; Hearing damage; In-utero acoustics; Noise pollution; Pregnancy; Prenatal sound exposure.

Fig 1:. Anatomical regions of datasets used in computational meshes.

This figure shows the surface boundaries of the three anatomical regions considered for datasets used in computational meshes: a GS339, b GS357 and c GS370. The anatomical regions are the maternal abdomen, the spine and the uterus.

Fig. 2:. Sound pressure level inside the uterus as a function of frequency for a unit amplitude incident plane wave.

Frequency response plots of the sound pressure level (SPL) inside the womb obtained for a unit amplitude plane wave travelling towards the front of the body, in the negative x direction. Such a plane wave is described mathematically by the real part of e^{−i(ωt−kx)} where k is the wave number in air and ω is the angular frequency. Three metrics of the sound pressure level inside the uterus are plotted for datasets GS339, GS357 and GS370. a, d and g correspond to the SPL resulting from the spatial RMS of the acoustic pressure magnitude inside the uterus; b, e and h describe the SPL associated with the l^∞-norm, effectively corresponding to the maximum pressure magnitude at the sampled points; c, f and i represent the SPL resulting from the acoustic pressure magnitude at the barycentre of the uterus. Uterus points within a solid angle of 0.5 steradian from the surface of the mesh were discarded in the analysis as the BEM can overestimate field potentials close to a surface. The field potential evaluation points for each dataset are displayed below.

Fig. 2:. Sound pressure level inside the uterus as a function of frequency for a unit amplitude incident plane wave.

Frequency response plots of the sound pressure level (SPL) inside the womb obtained for a unit amplitude plane wave travelling towards the front of the body, in the negative x direction. Such a plane wave is described mathematically by the real part of e^{−i(ωt−kx)} where k is the wave number in air and ω is the angular frequency. Three metrics of the sound pressure level inside the uterus are plotted for datasets GS339, GS357 and GS370. a, d and g correspond to the SPL resulting from the spatial RMS of the acoustic pressure magnitude inside the uterus; b, e and h describe the SPL associated with the l^∞-norm, effectively corresponding to the maximum pressure magnitude at the sampled points; c, f and i represent the SPL resulting from the acoustic pressure magnitude at the barycentre of the uterus. Uterus points within a solid angle of 0.5 steradian from the surface of the mesh were discarded in the analysis as the BEM can overestimate field potentials close to a surface. The field potential evaluation points for each dataset are displayed below.

Fig.3:. Sound pressure level maps at 5 kHz, 10 kHz and 20 kHz for dataset GS339 for an incident unit amplitude plane wave

SPL inside all anatomical regions for an incident unit amplitude plane wave travelling in the negative x direction. The acoustic attenuation coefficient in the uterus is that of amniotic fluid in a–f and that of muscle tissue in g–l. 3D maps of the SPL re 1 Pa are shown in a–c and g–i. d–f and j–k show a slice of the SPL re 1 Pa in the transverse plane passing through the barycentre of the uterus.

Fig.4:. Sound pressure level maps at 5 kHz, 10 kHz and 20 kHz for dataset GS357 for an incident unit amplitude plane wave

SPL inside all anatomical regions for an incident unit amplitude plane wave travelling in the negative x direction. The acoustic attenuation coefficient in the uterus is that of amniotic fluid in a–f and that of muscle tissue in g–l. 3D maps of the SPL re 1 Pa are shown in a–c and g–i. d–f and j–k show a slice of the SPL re 1 Pa in the transverse plane passing through the barycentre of the uterus.

Fig.5:. Sound pressure level maps at 5 kHz, 10 kHz and 20 kHz for dataset GS370 for an incident unit amplitude plane wave

SPL inside all anatomical regions for an incident unit amplitude plane wave travelling in the negative x direction. The acoustic attenuation coefficient in the uterus is that of amniotic fluid in a–f and that of muscle tissue in g–l. 3D maps of the SPL re 1 Pa are shown in a–c and g–i. d–f and j–l show a slice of the SPL re 1 Pa in the transverse plane passing through the barycentre of the uterus.

Fig.6:. Validation of computational model against the analytical solution for nested spheres: frequency response.

Sound pressure level transmission inside the inner sphere with dimensions representative of the uterus as a function of frequency for a unit amplitude incident plane wave travelling in the positive x direction for two concentric spheres obtained from a the SPL resulting from the spatial RMS of the acoustic pressure magnitude inside the inner sphere with two resonances shown at 3 kHz and 8.5 kHz, and b the acoustic pressure magnitude at the centre of the inner sphere. The outer sphere has a radius of 0.25 m and the inner sphere of 0.15 m. The exterior medium is air. The medium bounded by the exterior domain and the inner sphere has the properties of abdominal tissue and the inner sphere those of amniotic fluid.

Fig.7:. Validation of computational model against the analytical solution for nested spheres: acoustic pressure field visualisation

Acoustic pressure magnitude in the Cartesian x – y plane, describing the interactions between the incident plane wave and the concentric spheres of radii 0.25 m and 0.15 m, at excitation frequencies of 3 kHz, 8.5 kHz and 20 kHz. The first two frequencies correspond to the resonances identified in the spherical cavities in Figure 6 and the third to the upper limit of the human audio range. a, b and c are obtained using the analytical solution. b, d and f correspond to the nested BEM solution provided by OptimUS. The exterior medium is air, the outer sphere has the properties of abdominal tissue and the inner sphere those of amniotic fluid.

Fig. 8:. Impulse response generated from the acoustic pressure inside the uterus.

Impulse response generated from the complex acoustic pressure at a, the barycentre of the GS339 dataset uterus and b, the barycentre of the GS357 dataset uterus in response to a unit amplitude plane wave incident on the abdomen travelling in the negative x direction.