Lung hemorrhage at and near resonance: Pulse duration and pulse number

Research from our lab has shown that low-frequency (∼100–1000 Hz) underwater sound can produce mammalian lung hemorrhage. For adult mice, the pressure threshold for lung damage is ∼2 kPa for a 3-min continuous wave exposure at the lung resonance frequency (∼300 Hz). Sound-induced lung hemorrhage was studied for exposure below (200 Hz) and above (500 Hz) lung resonance. The threshold for lung damage is lowest for exposure at the lung resonance frequency. Furthermore, a series of experiments was performed to investigate effects of pulse duration and number of pulses on lung hemorrhage produced by exposure to underwater sound at lung resonance frequency. The resonance frequency of each mouse lung was determined using an acoustic scattering technique. In one set of experiments, the extent of lung hemorrhage was assessed for increasing pulse durations ranging from 1–180 s. In another set of experiments, extent of lung hemorrhage was assessed for increasing number of pulses. Extent of lung hemorrhage increased with increasing pulse duration and increasing number of pulses. The lung resonance frequency can shift higher or lower during sound exposure. The results of this work are relevant to establishing safety guidelines for swimmers and divers exposed to underwater sound fields.