title: Transcranial Doppler ultrasonographic evaluation of middle cerebral artery hemodynamics during mild hypothermia.
abstract: OBJECTIVE
  Induced hypothermia holds promise as an effective neuroprotective strategy following cerebral ischemia. The effect of mild hypothermia on cerebral hemodynamics is not well known. The authors investigated the influence of brain temperature on middle cerebral artery (MCA) mean flow velocity (MCA FV) and pulsatility index (MCA PI) in nonintubated, healthy volunteers undergoing mild induced hypothermia.
  
  
  METHODS
  Mild hypothermia (target tympanic membrane temperature [T tym] degrees C) was induced in subjects using the Arctic Sun Temperature Management System (Medivance, Inc, Louisville, CO). MCA FV and MCA PI were recorded bilaterally with a 2 MHz pulsed probe every 30 minutes via the transtemporal window.
  
  
  RESULTS
  Eighteen subjects (8 males, 10 females) 32 +/- 8 years of age were studied. Multivariate analysis indicated that MCA FV increased with increasing change in temperature (baseline tympanic temperature-tympanic temperature [DeltaT tym]) (P< .001), heart rate (HR) (P< .001), end-tidal CO 2(P= .025), arterial oxygen saturation (O2%) (P= .001), and with decreasing mean arterial blood pressure (P= .004). Multivariate analysis also indicated that ln(MCA PI) (natural logarithm of MCA PI) decreased with decreasing T tym(P< .001) and increasing HR (P< .001).
  
  
  CONCLUSIONS
  Mild induced hypothermia is associated with an increase in MCA FV and a decrease in MCA PI. The increase in MCA FV may be partially due to microcirculatory vasodilation.
authors.affiliation: University of South Alabama Stroke Center, 2541 Fillingim Street, Ste. 10-I, Mobile, AL 36617, USA. amahmood@usouthal.edu
authors.forename: M Asim
authors.initials: MA
authors.lastname: Mahmood
authors.forename: Marc E
authors.initials: ME
authors.lastname: Voorhees
authors.forename: Mel
authors.initials: M
authors.lastname: Parnell
authors.forename: Richard M
authors.initials: RM
authors.lastname: Zweifler
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002560:Cerebrovascular Circulation; D005260:Female; D006339:Heart Rate; D006801:Humans; D007036:Hypothermia, Induced; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging*; D010100:Oxygen / Q000097:blood; D011673:Pulsatile Flow; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D010100:Oxygen