3-DIMENSIONAL INTRAABDOMINAL SOUND PRESSURES IN SHEEP PRODUCED BY AIRBORNE STIMULI

OBJECTIVE: Our aims were to investigate how airborne sound was distrib uted within the abdominal cavity of sheep as function of frequency. ST UDY DESIGN: Airborne broad-band noise was measured with a hydrophone a t 45 locations within the abdomen of five nonpregnant sheep post morte m and with a microphone extraabdominally. Sound pressure attenuation p rovided 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 intraabd ominal distribution of sound pressures. RESULTS: Below 250 Hz sound pr essure was higher inside the animal than outside. Little attenuation ( < 10 dB) was found for sounds > 3000 Hz. Attenuation was greatest in t he center of the abdomen and least along the inner margin of the abdom en. Intraabdominal sound pressure level varied with frequency (p < 0.0 001) 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 ani mal effect (p = 0.18). CONCLUSION: During maternal exposure to airborn e, broadband noise the fetus could be subjected to intense sound press ures at low frequencies regardless of position within the uterus and a t high frequencies when positioned near the abdominal surface.