title: [Influence of continuous positive airway pressure (CPAP) on blood flow velocity in the venous vascular system of the liver -- duplex sonographic investigations].
abstract: OBJECTIVE
  In the last years, noninvasive techniques of artificial ventilation like continuous positive airway pressure (CPAP) have become more and more important. However, the effects of such procedures on the circulation of the hepatosplanchnic area are, except for the indocyanine green plasma clearance, not yet representative by means of noninvasive investigation methods.
  
  
  METHODS
  We studied maximum blood flow velocity in defined areas of hepatic and portal veins by duplex ultrasonography in 20 healthy volunteers (12 male, 8 female; age: 24,7 +/- 4,7 years [mean +/- SD]) before, during and after application of CPAP (10 cm H(2)O). As many measurements as possible were taken in both vascular systems. After division into five minute intervals arithmetical mean values were calculated for each interval. The experiment was divided into a control interval ("before CPAP"), three "CPAP" intervals and finally two "after CPAP" intervals. Heart rate and blood pressure were taken at the beginning of these intervals.
  
  
  RESULTS
  Compared with the control interval, maximum blood flow velocity in the area of the hepatic vein decreased significantly by 13,2 %, 16,8 % and 15,7 % (p < or = 0,001 in each case) during each of the three "CPAP" periods. In the portal venous area blood flow velocity decreased by 4,3 %, 8,8 % and 7,0 %, respectively, with a significant decrease only in the second "CPAP" interval (p < or = 0,005). After CPAP, changes returned to baseline within a few minutes. Heart rate and blood pressure showed no significant differences during the whole experiment.
  
  
  CONCLUSIONS
  Parameters taken in both venous vascular areas of the liver show clear correspondence with the results of former studies, which have been determined by means of more invasive investigation methods. Maximum blood flow velocity seems to be useful for monitoring liver blood flow and its individual time course during CPAP, noninvasively and semiquantitatively. Further trials under conditions of controlled mechanical ventilation should be performed to optimize ventilation strategies for the critically ill.
authors.affiliation: Abteilung Anästhesiologie, Intensivmedizin, Schmerztherapie, Universitätsklinikum Giessen. matthias.g.scheffler@chiru.med.uni-giessen.de
authors.forename: M
authors.initials: M
authors.lastname: Scheffler
authors.forename: V
authors.initials: V
authors.lastname: Klingmüller
authors.forename: M
authors.initials: M
authors.lastname: Born
authors.forename: C
authors.initials: C
authors.lastname: Pistofidou
authors.forename: G
authors.initials: G
authors.lastname: Hempelmann
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D045422:Continuous Positive Airway Pressure; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006503:Hepatic Veins / Q000502:physiology; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging*; D008102:Liver Circulation / Q000502:physiology*; D008297:Male; D011169:Portal Vein / Q000502:physiology; D018616:Ultrasonography, Doppler, Duplex