Abstract:

A study was undertaken to determine the response of the human lung to low-frequency underwater sound in the range of 20 to 500 Hz. Experiments were conducted in a 1100 gal tank inside a hyperbaric chamber. Lung responses were measured by three independent techniques: a hydrophone close to the chest, an accelerometer attached to the chest, and a noninvasive ultrasound measurement of the lung surface. Ten subjects were tested. Each subject was tested twice at ambient pressures of 0, 10, 60, and 120 ft of sea water (FSW). The dominant feature of the response was a strong resonance that occurred, on average, at 39 Hz at surface pressure and 71 Hz at a depth of 120 FSW. This appears to be the fundamental resonance of the lungs. The depth dependence indicates that lung stiffness is dominated by gas in the lungs with a small contribution from the chest wall. Resonance Q's were in the range of 5 to 7. There is evidence in the data of other low-frequency resonances that can be attributed to intestinal gas. Other than these, the lung acceleration response to incident pressure above resonance appears to be flat. [Work supported by ONR.]