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Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure

The ability to maintain adequate cerebral blood flow and oxygenation determines tolerance to central hypovolemia. We tested the hypothesis that acute hypoxemia during simulated blood loss in humans would cause impairments in cerebral blood flow control. Ten healthy subjects (32 ± 6 years, BMI 27 ± 2...

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Main Authors: van Helmond, Noud, Johnson, Blair D., Holbein, Walter W., Petersen‐Jones, Humphrey G., Harvey, Ronée E., Ranadive, Sushant M., Barnes, Jill N., Curry, Timothy B., Convertino, Victor A., Joyner, Michael J.
Format: Online Article Text
Language:English
Published: John Wiley and Sons Inc. 2018
Subjects:
Online Access:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5820424/
https://www.ncbi.nlm.nih.gov/pubmed/29464923
http://dx.doi.org/10.14814/phy2.13594
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author van Helmond, Noud
Johnson, Blair D.
Holbein, Walter W.
Petersen‐Jones, Humphrey G.
Harvey, Ronée E.
Ranadive, Sushant M.
Barnes, Jill N.
Curry, Timothy B.
Convertino, Victor A.
Joyner, Michael J.
author_facet van Helmond, Noud
Johnson, Blair D.
Holbein, Walter W.
Petersen‐Jones, Humphrey G.
Harvey, Ronée E.
Ranadive, Sushant M.
Barnes, Jill N.
Curry, Timothy B.
Convertino, Victor A.
Joyner, Michael J.
author_sort van Helmond, Noud
collection PubMed
description The ability to maintain adequate cerebral blood flow and oxygenation determines tolerance to central hypovolemia. We tested the hypothesis that acute hypoxemia during simulated blood loss in humans would cause impairments in cerebral blood flow control. Ten healthy subjects (32 ± 6 years, BMI 27 ± 2 kg·m(−2)) were exposed to stepwise lower body negative pressure (LBNP, 5 min at 0, −15, −30, and −45 mmHg) during both normoxia and hypoxia (F(i)O(2) = 0.12–0.15 O(2) titrated to an SaO(2) of ~85%). Physiological responses during both protocols were expressed as absolute changes from baseline, one subject was excluded from analysis due to presyncope during the first stage of LBNP during hypoxia. LBNP induced greater reductions in mean arterial pressure during hypoxia versus normoxia (MAP, at −45 mmHg: −20 ± 3 vs. −5 ± 3 mmHg, P < 0.01). Despite differences in MAP, middle cerebral artery velocity responses (MCAv) were similar between protocols (P = 0.41) due to increased cerebrovascular conductance index (CVCi) during hypoxia (main effect, P = 0.04). Low frequency MAP (at −45 mmHg: 17 ± 5 vs. 0 ± 5 mmHg(2), P = 0.01) and MCAv (at −45 mmHg: 4 ± 2 vs. −1 ± 1 cm·s(−2), P = 0.04) spectral power density, as well as low frequency MAP‐mean MCAv transfer function gain (at −30 mmHg: 0.09 ± 0.06 vs. −0.07 ± 0.06 cm·s(−1)·mmHg(−1), P = 0.04) increased more during hypoxia versus normoxia. Contrary to our hypothesis, these findings support the notion that cerebral blood flow control is not impaired during exposure to acute hypoxia and progressive central hypovolemia despite lower MAP as a result of compensated increases in cerebral conductance and flow variability.
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spelling pubmed-58204242018-02-26 Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure van Helmond, Noud Johnson, Blair D. Holbein, Walter W. Petersen‐Jones, Humphrey G. Harvey, Ronée E. Ranadive, Sushant M. Barnes, Jill N. Curry, Timothy B. Convertino, Victor A. Joyner, Michael J. Physiol Rep Original Research The ability to maintain adequate cerebral blood flow and oxygenation determines tolerance to central hypovolemia. We tested the hypothesis that acute hypoxemia during simulated blood loss in humans would cause impairments in cerebral blood flow control. Ten healthy subjects (32 ± 6 years, BMI 27 ± 2 kg·m(−2)) were exposed to stepwise lower body negative pressure (LBNP, 5 min at 0, −15, −30, and −45 mmHg) during both normoxia and hypoxia (F(i)O(2) = 0.12–0.15 O(2) titrated to an SaO(2) of ~85%). Physiological responses during both protocols were expressed as absolute changes from baseline, one subject was excluded from analysis due to presyncope during the first stage of LBNP during hypoxia. LBNP induced greater reductions in mean arterial pressure during hypoxia versus normoxia (MAP, at −45 mmHg: −20 ± 3 vs. −5 ± 3 mmHg, P < 0.01). Despite differences in MAP, middle cerebral artery velocity responses (MCAv) were similar between protocols (P = 0.41) due to increased cerebrovascular conductance index (CVCi) during hypoxia (main effect, P = 0.04). Low frequency MAP (at −45 mmHg: 17 ± 5 vs. 0 ± 5 mmHg(2), P = 0.01) and MCAv (at −45 mmHg: 4 ± 2 vs. −1 ± 1 cm·s(−2), P = 0.04) spectral power density, as well as low frequency MAP‐mean MCAv transfer function gain (at −30 mmHg: 0.09 ± 0.06 vs. −0.07 ± 0.06 cm·s(−1)·mmHg(−1), P = 0.04) increased more during hypoxia versus normoxia. Contrary to our hypothesis, these findings support the notion that cerebral blood flow control is not impaired during exposure to acute hypoxia and progressive central hypovolemia despite lower MAP as a result of compensated increases in cerebral conductance and flow variability. John Wiley and Sons Inc. 2018-02-21 /pmc/articles/PMC5820424/ /pubmed/29464923 http://dx.doi.org/10.14814/phy2.13594 Text en © 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society. This is an open access article under the terms of the Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Original Research
van Helmond, Noud
Johnson, Blair D.
Holbein, Walter W.
Petersen‐Jones, Humphrey G.
Harvey, Ronée E.
Ranadive, Sushant M.
Barnes, Jill N.
Curry, Timothy B.
Convertino, Victor A.
Joyner, Michael J.
Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title_full Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title_fullStr Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title_full_unstemmed Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title_short Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
title_sort effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure
topic Original Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5820424/
https://www.ncbi.nlm.nih.gov/pubmed/29464923
http://dx.doi.org/10.14814/phy2.13594
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