Linked Life Data

16926845

Source:http://linkedlifedata.com/resource/pubmed/id/16926845

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
2007-3-23
pubmed:abstractText
Acute hypoxia directly causes cerebral arteriole vasodilation and also stimulates peripheral chemoreceptors to change autonomic neural activity. These changes may alter cerebral vascular modulation. We therefore hypothesized that dynamic cerebral autoregulation would be altered during acute exposure to hypoxia. Fifteen healthy men were examined under normoxic (21%) and hypoxic conditions. Oxygen concentrations were decreased in stepwise fashion to 19%, 17%, and 15%, for 10 mins at each level. Mean blood pressure (MBP) in the radial artery was measured via tonometry, and cerebral blood flow velocity (CBFV) in the middle cerebral artery was measured by transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis of beat-by-beat changes in MBP and CBFV. Arterial oxygen saturation decreased significantly during hypoxia, while end-tidal CO2 and respiratory rate were unchanged, as was steady-state CBFV. With 15% O2, very-low-frequency power of MBP and CBFV variability increased significantly by 185% and 282%, respectively. Moreover, transfer function coherence (21% O2, 0.46+/-0.04; 15% O2, 0.64+/-0.04; P=0.028) and gain (21% O2, 0.61+/-0.05 cm/secs/mm Hg; 15% O2, 0.86+/-0.08 cm/secs/mm Hg; P=0.035) in the very-low-frequency range increased significantly by 53% and 48% with 15% O2, respectively. However, these indices were unchanged in low- and high-frequency ranges. Acute hypoxia thus increases arterial pressure oscillations and dependence of cerebral blood flow (CBF) fluctuations on blood pressure oscillations, resulting in apparent increases in CBF fluctuations in the very-low-frequency range. Hypoxia may thus impair dynamic cerebral autoregulation in this range. However, these changes were significant only with hypoxia at 15% O2, suggesting a possible threshold for such changes.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0271-678X
pubmed:author
pubmed:issnType
Print
pubmed:volume
27
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
776-84
pubmed:meshHeading
pubmed:year
2007
pubmed:articleTitle
Acute exposure to normobaric mild hypoxia alters dynamic relationships between blood pressure and cerebral blood flow at very low frequency.
pubmed:affiliation
Department of Hygiene and Space Medicine, Nihon University School of Medicine, Tokyo, Japan. kiwasaki@med.nihon-u.ac.jp
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't