PMID- 11566072
OWN - NLM
STAT- MEDLINE
DCOM- 20020418
LR  - 20161124
IS  - 0143-5221 (Print)
IS  - 0143-5221 (Linking)
VI  - 101
IP  - 4
DP  - 2001 Oct
TI  - Carbon dioxide, critical closing pressure and cerebral haemodynamics prior to 
      vasovagal syncope in humans.
PG  - 351-8
AB  - The cerebrovascular changes that occur prior to vasovagal syncope (VVS) are 
      unclear, with both increases and decreases in cerebrovascular resistance being 
      reported during pre-syncope. This study assessed the cerebrovascular responses, 
      and their potential underlying mechanisms, that occurred before VVS induced by 
      head-up tilt (HUT). Groups of 65 normal subjects with no previous history of 
      syncope and of 16 patients with recurrent VVS were subjected to 70 degrees HUT 
      for up to 30 min. Bilateral middle cerebral artery (MCA) cerebral blood flow 
      velocities (CBFVs) were measured using transcranial Doppler ultrasound, along 
      with simultaneous measures of MCA blood pressure, heart rate, and end-tidal and 
      transcutaneous carbon dioxide concentrations. All 16 patients and 14 of the 
      control subjects developed VVS during HUT. During pre-syncope, mean CBFV 
      declined, due predominantly to a decrease in diastolic rather than systolic CBFV 
      (decreases of 44.5+/-19.8% and 6.3+/-12.9% respectively; P<0.0001). CO(2) levels 
      and indices of cerebrovascular resistance decreased during pre-syncope, while 
      critical closing pressure (CrCP) increased to levels approaching MCA diastolic 
      blood pressure before decreasing precipitously on syncope. Pre-syncopal changes 
      were similar in syncopal patients and syncopal controls. CrCP, therefore, rises 
      during pre-syncope, possibly related to progressive hypocapnia, and may account 
      for the relatively greater fall in diastolic CBFV. Falls in cerebrovascular 
      resistance, therefore, may be offset by rises in CrCP due to hypocapnia, leading 
      to diminished cerebral blood flow during pre-syncope.
FAU - Carey, B J
AU  - Carey BJ
AD  - Division of Medicine for the Elderly, University of Leicester, Glenfield 
      Hospital, Groby Road, Leicester LE3 9QP, UK. brian.carey@uhl-tr.nhs.uk
FAU - Eames, P J
AU  - Eames PJ
FAU - Panerai, R B
AU  - Panerai RB
FAU - Potter, J F
AU  - Potter JF
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - Clin Sci (Lond)
JT  - Clinical science (London, England : 1979)
JID - 7905731
RN  - 142M471B3J (Carbon Dioxide)
SB  - IM
MH  - Adolescent
MH  - Adult
MH  - Aged
MH  - Aged, 80 and over
MH  - Blood Pressure
MH  - Carbon Dioxide/*blood
MH  - Cerebral Arteries/diagnostic imaging/physiopathology
MH  - *Cerebrovascular Circulation
MH  - Female
MH  - Hemodynamics
MH  - Homeostasis
MH  - Humans
MH  - Male
MH  - Middle Aged
MH  - Recurrence
MH  - Syncope, Vasovagal/blood/*physiopathology
MH  - Ultrasonography, Doppler, Transcranial
MH  - Vascular Resistance
EDAT- 2001/09/22 10:00
MHDA- 2002/04/19 10:01
CRDT- 2001/09/22 10:00
PHST- 2001/09/22 10:00 [pubmed]
PHST- 2002/04/19 10:01 [medline]
PHST- 2001/09/22 10:00 [entrez]
PST - ppublish
SO  - Clin Sci (Lond). 2001 Oct;101(4):351-8.