We examined the impact of progressive hypotension with and without hypocapnia on regional extracranial cerebral blood flow (CBF) and intracranial velocities. Participants underwent progressive lower-body negative pressure (LBNP) until pre-syncope to inflict hypotension. End-tidal carbon dioxide was clamped at baseline levels (isocapnic trial) or uncontrolled (poikilocapnic trial). Middle cerebral artery (MCA) and posterior cerebral artery (PCA) blood velocities (transcranial Doppler; TCD), heart rate, blood pressure and end-tidal carbon dioxide were obtained continuously. Measurements of internal carotid artery (ICA) and vertebral artery (VA) blood flow (ICABF and VABF respectively) were also obtained. Overall, blood pressure was reduced by ∼20% from baseline in both trials (P<0.001). In the isocapnic trial, end-tidal carbon dioxide was successfully clamped at baseline with hypotension, whereas in the poikilocapnic trial it was reduced by 11.1 mmHg (P<0.001) with hypotension. The decline in the ICABF with hypotension was comparable between trials (−139±82 ml; ∼30%; P<0.0001); however, the decline in the VABF was −28±22 ml/min (∼21%) greater in the poikilocapnic trial compared with the isocapnic trial (P=0.002). Regardless of trial, the blood flow reductions in ICA (−26±14%) and VA (−27±14%) were greater than the decline in MCA (−21±15%) and PCA (−19±10%) velocities respectively (P≤0.01). Significant reductions in the diameter of both the ICA (∼5%) and the VA (∼7%) contributed to the decline in cerebral perfusion with systemic hypotension, independent of hypocapnia. In summary, our findings indicate that blood flow in the VA, unlike the ICA, is sensitive to changes hypotension and hypocapnia. We show for the first time that the decline in global CBF with hypotension is influenced by arterial constriction in the ICA and VA. Additionally, our findings suggest TCD measures of blood flow velocity may modestly underestimate changes in CBF during hypotension with and without hypocapnia, particularly in the posterior circulation.
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Research Article|
April 24 2015
Impact of transient hypotension on regional cerebral blood flow in humans
Nia C.S. Lewis;
*Centre of Heart, Lung and Vascular Health, University of British Columbia, Kelowna, Canada
Correspondence: Dr Nia C.S. Lewis (email [email protected]).
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Kurt J. Smith;
Kurt J. Smith
*Centre of Heart, Lung and Vascular Health, University of British Columbia, Kelowna, Canada
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Anthony R. Bain;
Anthony R. Bain
*Centre of Heart, Lung and Vascular Health, University of British Columbia, Kelowna, Canada
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Kevin W. Wildfong;
Kevin W. Wildfong
*Centre of Heart, Lung and Vascular Health, University of British Columbia, Kelowna, Canada
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Tianne Numan;
Tianne Numan
†MIRA, University of Twente, Enschede, The Netherlands
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Philip N. Ainslie
Philip N. Ainslie
*Centre of Heart, Lung and Vascular Health, University of British Columbia, Kelowna, Canada
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Publisher: Portland Press Ltd
Received:
November 18 2014
Revision Received:
January 15 2015
Accepted:
February 20 2015
Accepted Manuscript online:
February 20 2015
Online ISSN: 1470-8736
Print ISSN: 0143-5221
© The Authors Journal compilation © 2015 Biochemical Society
2015
Clin Sci (Lond) (2015) 129 (2): 169–178.
Article history
Received:
November 18 2014
Revision Received:
January 15 2015
Accepted:
February 20 2015
Accepted Manuscript online:
February 20 2015
Citation
Nia C.S. Lewis, Kurt J. Smith, Anthony R. Bain, Kevin W. Wildfong, Tianne Numan, Philip N. Ainslie; Impact of transient hypotension on regional cerebral blood flow in humans. Clin Sci (Lond) 1 July 2015; 129 (2): 169–178. doi: https://doi.org/10.1042/CS20140751
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