Thomas N. Lewis
James S. Martin
Peter H. Rogers
School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405
Because of their high compliance, the lungs are probably more susceptible to injury from low-frequency underwater sound than any other part of the anatomy. Therefore, it is desirable to have a complete understanding of the vibrational response of the lungs to underwater sound. The NIVAMS (noninvasive vibration amplitude measurement system) was used to measure the response of the lungs of an animal model (domestic pigs) to low-frequency underwater sound. NIVAMS uses continuous wave ultrasound to measure lung vibrational displacement amplitudes in vivo. Advantages of the NIVAMS are that it is noninvasive (no surgery is required to make the measurements) and that it is nonintrusive (the motion is unaltered by the measurement process). Displacements were measured in two locations, between the ribs and upward through the diaphragm. A PUBA (porcine underwater breathing apparatus) was developed to allow measurements to be made below the water surface. Displacements measurements were found to be significantly larger than the particle motions associated with the acoustic pressure driving the air filled lungs. Multiple resonances were found in the response curves. The necessity for the use of live, intact subjects was demonstrated by differences in the response curves for other conditions. [Research supported by ONR.]