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Alterations in arterial CO2 rather than pH affect the kinetics of neurovascular coupling in humans

journal contribution
posted on 01.07.2021, 13:46 by Hannah G Caldwell, Connor A Howe, Ryan L Hoiland, Jay MJR Carr, Carter J Chalifoux, Courtney V Brown, Alexander Patrician, Joshua C Tremblay, Ronney B Panerai, Thompson G Robinson, Jatinder S Minhas, Philip N Ainslie
Elevations in cerebral metabolism necessitate appropriate coordinated and localized increases in cerebral blood flow (i.e. neurovascular coupling; NVC). Recent pre-clinical work indicates that arterial urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0009 (urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0010) mediates NVC independently of arterial/extracellular pH; this has yet to be experimentally tested in humans. The goal of this study was to investigate the hypotheses that: (1) the NVC response would be unaffected by acute experimentally elevated arterial pH; rather, urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0011 would regulate any changes in NVC; and (2) stepwise respiratory alkalosis and acidosis would each progressively reduce the NVC response. Ten healthy males completed a standardized visual stimulus-evoked NVC test during matched stepwise iso-oxic alterations in urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0012 (hypocapnia: −5, −10 mmHg; hypercapnia: +5, +10 mmHg) prior to and following intravenous NaHCO3 (8.4%, 50 mEq/50 ml) that elevated arterial pH (7.406 ± 0.019 vs. 7.457 ± 0.029; P < 0.001) and [HCO3–] (26.2 ± 1.5 vs. 29.3 ± 0.9 mEq/l; P < 0.001). Although the NVC response was collectively attenuated by 27–38% with −10 mmHg urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0013 (stage post hoc: all P < 0.05), this response was unaltered following NaHCO3 (all P > 0.05) irrespective of the higher pH (P = 0.002) at each matched stage of urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0014 (P = 0.417). The absolute peak change was reduced by −19 ± 41% with +10 mmHg urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0015 irrespective of acutely elevated arterial pH/[HCO3–] (stage post hoc: P = 0.022). The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively; stage effect: P < 0.001). Overall, these findings indicate that temporal patterns in NVC are acutely regulated by urn:x-wiley:00223751:media:tjp14740:tjp14740-math-0016 rather than arterial pH per se in the setting of acute metabolic alkalosis in humans.

History

Author affiliation

Department of Cardiovascular Sciences

Version

AM (Accepted Manuscript)

Published in

The Journal of physiology

Publisher

Wiley

issn

0022-3751

eissn

1469-7793

Acceptance date

08/06/2021

Copyright date

2021

Available date

09/06/2022

Spatial coverage

England

Language

eng