title: Superthreshold behavior of ultrasound-induced lung hemorrhage in adult rats: role of pulse repetition frequency and exposure duration revisited.
abstract: OBJECTIVE
  The purpose of this study was to augment and reevaluate the ultrasound-induced lung hemorrhage findings of a previous 5 x 3 factorial design study (Ultrasound Med Biol 2001; 27:267-277) that evaluated the role of pulse repetition frequency (PRF: 25, 50, 100, 250, and 500 Hz) and exposure duration (ED; 5, 10, and 20 s) on ultrasound-induced lung hemorrhage at an in situ (at the pleural surface) peak rarefactional pressure [pr(in situ)] of 12.3 MPa; only PRF was found to be significant. However, saturation (response plateau) due to the high pr(in situ) might have skewed the results. In this follow-up 3 x 3 factorial design study, a wider range of PRFs and EDs were used at a lower pr(in situ).
  
  
  METHODS
  Sprague Dawley rats (n=198) were divided into 18 ultrasonically exposed groups (10 rats per group) and 6 sham groups (3 per group). The 3 x 3 factorial design study (PRF: 17, 170, and 1700 Hz; ED: 5, 31.6, and 200 s) was conducted at 2 frequencies (2.8 and 5.6 MHz). The p(r(in situ)) was 6.1 MPa. Logistic regression analysis evaluated lesion occurrence, and Gaussian tobit analysis evaluated lesion depth and surface area.
  
  
  RESULTS
  Frequency did not have a significant effect, so the analysis combined results for the 2 frequencies. For lesion occurrence and sizes, the main effects for PRF and ED were not significant. The interaction term was highly significant, indicating a strong dependence of lesion occurrence and size on the total number of pulses (PRF x ED).
  
  
  CONCLUSIONS
  The results of both studies are consistent with the hypothesis that the total number of pulses is an important factor in the genesis of ultrasound-induced lung hemorrhage.
authors.affiliation: Jr, Bioacoustics Research Laboratory, Department of Electrical and Computer Engineering, University of Illinois, 405 N Mathews, Urbana, IL 61801 USA. wdo@uiuc.edu
authors.forename: William D
authors.initials: WD
authors.lastname: O'Brien
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Simpson
authors.forename: Leon A
authors.initials: LA
authors.lastname: Frizzell
authors.forename: James F
authors.initials: JF
authors.lastname: Zachary
mesh_terms: D000367:Age Factors; D000818:Animals; D005260:Female; D006470:Hemorrhage / Q000209:etiology*; D008171:Lung Diseases / Q000209:etiology*; D015233:Models, Statistical; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014465:Ultrasonics