Cerebral blood flow, frontal lobe oxygenation and intra-arterial blood pressure during sprint exercise in normoxia and severe acute hypoxia in humans

J Cereb Blood Flow Metab. 2018 Jan;38(1):136-150. doi: 10.1177/0271678X17691986. Epub 2017 Feb 10.

Abstract

Cerebral blood flow (CBF) is regulated to secure brain O2 delivery while simultaneously avoiding hyperperfusion; however, both requisites may conflict during sprint exercise. To determine whether brain O2 delivery or CBF is prioritized, young men performed sprint exercise in normoxia and hypoxia (PIO2 = 73 mmHg). During the sprints, cardiac output increased to ∼22 L min-1, mean arterial pressure to ∼131 mmHg and peak systolic blood pressure ranged between 200 and 304 mmHg. Middle-cerebral artery velocity (MCAv) increased to peak values (∼16%) after 7.5 s and decreased to pre-exercise values towards the end of the sprint. When the sprints in normoxia were preceded by a reduced PETCO2, CBF and frontal lobe oxygenation decreased in parallel ( r = 0.93, P < 0.01). In hypoxia, MCAv was increased by 25%, due to a 26% greater vascular conductance, despite 4-6 mmHg lower PaCO2 in hypoxia than normoxia. This vasodilation fully accounted for the 22 % lower CaO2 in hypoxia, leading to a similar brain O2 delivery during the sprints regardless of PIO2. In conclusion, when a conflict exists between preserving brain O2 delivery or restraining CBF to avoid potential damage by an elevated perfusion pressure, the priority is given to brain O2 delivery.

Keywords: Exercise; cerebral blood flow; cerebral haemodynamics; high altitude; hypertension.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Arterial Pressure / physiology*
  • Cerebrovascular Circulation / physiology*
  • Exercise / physiology*
  • Frontal Lobe / blood supply*
  • Hemodynamics / physiology*
  • Humans
  • Hypoxia / physiopathology
  • Male
  • Oxygen Consumption / physiology
  • Young Adult