title: Flow dynamics of QW7437, a new dodecafluoropentane ultrasound contrast agent, in the microcirculation: microvascular mechanisms for persistent tissue echo enhancement.
abstract: OBJECTIVE
  The purpose of this study was to test the hypothesis that a subgroup of QW7437 microbubbles, dodecafluoropentane-based ultrasound contrast microspheres, resides for prolonged periods in the microvasculature.
  
  
  BACKGROUND
  QW7437 produces echo enhancement in myocardium which may persist relatively longer than opacification in the left ventricular cavity. The mechanism for this persistent enhancement remains unknown.
  
  
  METHODS
  The transit of fluorescently labeled erythrocytes was examined by fluorescence intravital microscopy in the microvessels in five rat mesenteries. Ten rats were used to observe the behavior of fluorescently labeled QW7437 microbubbles in the mesenteric microcirculation.
  
  
  RESULTS
  There was no significant change in erythrocyte velocity in the arterioles and venules after the administration of QW7437 microbubbles (0.05 ml/kg) preactivated by negative hydrodynamic pressure. Of 552 microbubbles observed in four arterioles and five capillaries, 549 (99.5%) passed without stoppage (> or = 0.1 s stoppage); only one stopped transiently in arteriole and two in capillaries, each for <0.5 s. Sixty-five of 478 microbubbles (13.6%) observed in six postcapillary venules 11 to 30 microm in diameter and 24 of 408 microbubbles (5.9%) in four venules 31 to 50 microm in diameter stopped transiently (0.1 to 180 s) with an attachment to venular endothelium; the remaining microbubbles passed through the venules without stoppage.
  
  
  CONCLUSIONS
  Prolonged survival as microbubbles in the circulation and transient stoppage of a subgroup of microbubbles in the microvasculature, particularly in venules, are potential mechanisms for the persistent tissue echo enhancement by QW7437 microbubbles during contrast echocardiography.
authors.affiliation: Department of Medicine, University of California at San Diego, La Jolla 92093-0412, USA.
authors.forename: T
authors.initials: T
authors.lastname: Yasu
authors.forename: G W
authors.initials: GW
authors.lastname: Schmid-Schönbein
authors.forename: B
authors.initials: B
authors.lastname: Cotter
authors.forename: A N
authors.initials: AN
authors.lastname: DeMaria
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D003287:Contrast Media; D004452:Echocardiography; D004912:Erythrocytes; D005456:Fluorescent Dyes; D005466:Fluorocarbons; D008643:Mesentery / Q000098:blood supply; D008833:Microcirculation / Q000000981:diagnostic imaging*; D008856:Microscopy, Fluorescence; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003287:Contrast Media; D005456:Fluorescent Dyes; D005466:Fluorocarbons; C109298:QW7437