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UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude.

Publication ,  Journal Article
Howe, CA; Ainslie, PN; Tremblay, JC; Carter, HH; Patrician, A; Stembridge, M; Williams, A; Drane, AL; Delorme, E; Rieger, MG; Tymko, MM ...
Published in: Exp Physiol
December 2019

NEW FINDINGS: What is the central question of this study? The aim was to evaluate the degree to which increases in haematocrit alter cerebral blood flow and cerebral oxygen delivery during acclimatization to high altitude. What is the main finding and its importance? Through haemodilution, we determined that, after 1 week of acclimatization, the primary mechanism contributing to the cerebral blood flow response during acclimatization is an increase in haemoglobin and haematocrit. The remaining contribution to the cerebral blood flow response during acclimatization is likely to be attributable to ventilatory acclimatization. ABSTRACT: At high altitude, an increase in haematocrit (Hct) is achieved through altitude-induced diuresis and erythropoiesis, both of which result in increased arterial oxygen content. Given the impact of alterations in Hct on oxygen content, haemoconcentration has been hypothesized to mediate, in part, the attenuation of the initial elevation in cerebral blood flow (CBF) at high altitude. To test this hypothesis, healthy men (n = 13) ascended to 5050 m over 9 days without the aid of prophylactic acclimatization medications. After 1 week of acclimatization at 5050 m, participants were haemodiluted by rapid saline infusion (2.10 ± 0.28 l) to return Hct towards pre-acclimatization values. Arterial blood gases, Hct, global CBF (duplex ultrasound) and haemodynamic variables were measured after initial arrival at 5050 m and after 1 week of acclimatization at high altitude, before and after the haemodilution protocol. After 1 week at 5050 m, the Hct increased from 42.5 ± 2.5 to 49.6 ± 2.5% (P < 0.001), and it was subsequently reduced to 45.6 ± 2.3% (P < 0.001) after haemodilution. Global CBF decreased from 844 ± 160 to 619 ± 136 ml min-1 (P = 0.033) after 1 week of acclimatization and increased to 714 ± 204 ml min -1 (P = 0.045) after haemodilution. Despite the significant changes in Hct, and thus oxygen content, cerebral oxygen delivery was unchanged at all time points. Furthermore, these observations occurred in the absence of any changes in mean arterial blood pressure, cardiac output, arterial blood pH or oxygen saturation pre- and posthaemodilution. These data highlight the influence of Hct in the regulation of CBF and are the first to demonstrate experimentally that haemoconcentration contributes to the reduction in CBF during acclimatization to altitude.

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Published In

Exp Physiol

DOI

EISSN

1469-445X

Publication Date

December 2019

Volume

104

Issue

12

Start / End Page

1963 / 1972

Location

England

Related Subject Headings

  • Physiology
  • Nepal
  • Male
  • Humans
  • Hematocrit
  • Expeditions
  • Cerebrovascular Circulation
  • Blood Volume
  • Altitude
  • Adult
 

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Howe, C. A., Ainslie, P. N., Tremblay, J. C., Carter, H. H., Patrician, A., Stembridge, M., … Hoiland, R. L. (2019). UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude. Exp Physiol, 104(12), 1963–1972. https://doi.org/10.1113/EP087663
Howe, Connor A., Philip N. Ainslie, Joshua C. Tremblay, Howard H. Carter, Alex Patrician, Mike Stembridge, Alex Williams, et al. “UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude.Exp Physiol 104, no. 12 (December 2019): 1963–72. https://doi.org/10.1113/EP087663.
Howe CA, Ainslie PN, Tremblay JC, Carter HH, Patrician A, Stembridge M, et al. UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude. Exp Physiol. 2019 Dec;104(12):1963–72.
Howe, Connor A., et al. “UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude.Exp Physiol, vol. 104, no. 12, Dec. 2019, pp. 1963–72. Pubmed, doi:10.1113/EP087663.
Howe CA, Ainslie PN, Tremblay JC, Carter HH, Patrician A, Stembridge M, Williams A, Drane AL, Delorme E, Rieger MG, Tymko MM, Gasho C, Santoro A, MacLeod DB, Hoiland RL. UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude. Exp Physiol. 2019 Dec;104(12):1963–1972.
Journal cover image

Published In

Exp Physiol

DOI

EISSN

1469-445X

Publication Date

December 2019

Volume

104

Issue

12

Start / End Page

1963 / 1972

Location

England

Related Subject Headings

  • Physiology
  • Nepal
  • Male
  • Humans
  • Hematocrit
  • Expeditions
  • Cerebrovascular Circulation
  • Blood Volume
  • Altitude
  • Adult