Cerebral O2 and CO2 transport in isovolumic haemodilution: Compensation of cerebral delivery of O2 and maintenance of cerebrovascular reactivity to CO2

Jay MJR Carr, Philip N Ainslie, David B Macleod, Joshua C Tremblay, Daniela Nowak-Flück, Connor A Howe, Mike Stembridge, Alexander Patrician, Geoff B Coombs, Benjamin S Stacey, Damian M Bailey, Daniel J Green, Ryan L Hoiland

Research output: Contribution to journalArticlepeer-review

Abstract

This study investigated the influence of acute reductions in arterial O2 content (CaO2) via isovolumic haemodilution on global cerebral blood flow (gCBF) and cerebrovascular CO2 reactivity (CVR) in 11 healthy males (age; 28 ± 7 years: body mass index; 23 ± 2 kg/m2). Radial artery and internal jugular vein catheters provided measurement of blood pressure and gases, quantification of cerebral metabolism, cerebral CO2 washout, and trans-cerebral nitrite exchange (ozone based chemiluminescence). Prior to and following haemodilution, the partial pressure of arterial CO2 (PaCO2) was elevated with dynamic end-tidal forcing while gCBF was measured with duplex ultrasound. CVR was determined as the slope of the gCBF response and PaCO2. Replacement of ∼20% of blood volume with an equal volume of 5% human serum albumin (Alburex® 5%) reduced haemoglobin (13.8 ± 0.8 vs. 11.3 ± 0.6 g/dL; P < 0.001) and CaO2 (18.9 ± 1.0 vs 15.0 ± 0.8 mL/dL P < 0.001), elevated gCBF (+18 ± 11%; P = 0.002), preserved cerebral oxygen delivery (P = 0.49), and elevated CO2 washout (+11%; P = 0.01). The net cerebral uptake of nitrite (11.6 ± 14.0 nmol/min; P = 0.027) at baseline was abolished following haemodilution (−3.6 ± 17.9 nmol/min; P = 0.54), perhaps underpinning the conservation of CVR (61.7 ± 19.0 vs. 69.0 ± 19.2 mL/min/mmHg; P = 0.23). These findings demonstrate that the cerebrovascular responses to acute anaemia in healthy humans are sufficient to support the maintenance of CVR.
Original languageEnglish
Number of pages16
JournalJournal of Cerebral Blood Flow and Metabolism
Volume00
Issue number00
Early online date21 Sep 2022
DOIs
Publication statusE-pub ahead of print - 21 Sep 2022

Keywords

  • Hypoxaemia
  • hypercapnia
  • haemoglobin
  • anaemia
  • cerebral blood flow
  • nitric oxide

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