title: Microembolic signal counts increase during hyperbaric exposure in patients with prosthetic heart valves.
abstract: BACKGROUND
  Patients with prosthetic heart valves have an increased risk of thromboembolic events, and transcranial Doppler sonography reveals microembolic signals. Whereas microembolic signals were initially assumed to be of particulate matter, recent studies suggest that they are partially gaseous in origin. If this is true, alteration of environmental pressure should change microembolic signal counts. We undertook this study to evaluate the influence of hyperbaric exposure on microembolic signal counts in persons with prosthetic heart valves.
  
  
  RESULTS
  Microembolic signal counts were monitored by transcranial Doppler sonography of both middle cerebral arteries under normobaria (normobaria 1), 2 subsequent periods of hyperbaria (2.5 and 1.75 bar), and a second period of normobaria (normobaria 2) in 15 patients with prosthetic heart valves. Each monitoring period lasted 30 minutes. Compression and decompression rates were 0.1 bar/min. Microembolic signal counts increased from 20 (12-78) at normobaria 1 to 79 (30-165) at 2.5 bar (P <.01 vs normobaria 1 and 2), decreased to 44 (18-128) at 1.75 bar (P <.01 vs normobaria 1 and 2.5 bar; P <.001 vs normobaria 2), and returned to 20 (8-96) at normobaria 2 (values are medians and 95% confidence intervals).
  
  
  CONCLUSIONS
  Our results strongly suggest that gaseous bubbles are underlying material for part of the microembolic signals detected in patients with prosthetic heart valves.
authors.affiliation: Department of Neurology, University of Zurich, Switzerland. ralf.baumgartner@nos.usz.ch
authors.forename: R W
authors.initials: RW
authors.lastname: Baumgartner
authors.forename: A
authors.initials: A
authors.lastname: Frick
authors.forename: C
authors.initials: C
authors.lastname: Kremer
authors.forename: E
authors.initials: E
authors.lastname: Oechslin
authors.forename: E
authors.initials: E
authors.lastname: Russi
authors.forename: J
authors.initials: J
authors.lastname: Turina
authors.forename: D
authors.initials: D
authors.lastname: Georgiadis
mesh_terms: D001021:Aortic Valve; D005260:Female; D006350:Heart Valve Prosthesis; D006801:Humans; D006931:Hyperbaric Oxygenation; D020766:Intracranial Embolism / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging; D008943:Mitral Valve; D015588:Observer Variation; D017585:Ultrasonography, Doppler, Transcranial