Lung damage from exposure to pulsed ultrasound.

Motivated by a recent finding that threshold pressures for hemorrhage in mouse lung exposed to the fields of an electrohydraulic lithotripter were less than 2 MPa, we extended the exposures to pulsed ultrasound. Sharply defined thresholds of the order of 1 MPa were found with 10 microseconds length pulses and roughly twice that value for 1 microsecond pulses. The thresholds at 4 MHz are greater than at 1 MHz. The thresholds are comparable for focused and unfocused fields. As would be expected for a cavitation-like phenomenon, temporal average intensity is a very poor predictor of this effect. In the extreme case, lesions were found at temporal average intensities on the order of 1 mW/cm2.