Three-dimensional intraabdominal sound pressures in sheep produced by airborne stimuli.

OBJECTIVE

Our aims were to investigate how airborne sound was distributed within the abdominal cavity of sheep as function of frequency.

STUDY DESIGN

Airborne broad-band noise was measured with a hydrophone at 45 locations within the abdomen of five nonpregnant sheep post mortem and with a microphone extraabdominally. Sound pressure attenuation provided by the abdomen and its contents was determined for frequencies between 50 and 5000 Hz. An analysis of variance was applied to assess the effects of frequency, hydrophone location, and animal on intraabdominal distribution of sound pressures.

RESULTS

Below 250 Hz sound pressure was higher inside the animal than outside. Little attenuation (< 10 dB) was found for sounds > 3000 Hz. Attenuation was greatest in the center of the abdomen and least along the inner margin of the abdomen. Intraabdominal sound pressure level varied with frequency (p < 0.0001) and with position of the hydrophone in the cross-sectional plane (p < 0.005) but not in the sagittal plane (p = 0.51). There was no animal effect (p = 0.18).

CONCLUSION

During maternal exposure to airborne, broadband noise the fetus could be subjected to intense sound pressures at low frequencies regardless of position within the uterus and at high frequencies when positioned near the abdominal surface.