Changes of Cerebral Blood Flow during Short-Term Exposure to Normobaric Hypoxia

Abstract

Decreased arterial partial oxygen pressure (PaO2) below a certain level presents a strong stimulus for increasing cerebral blood flow. Although several field studies examined the time course of global cerebral blood flow (gCBF) changes during hypoxia at high altitude, little was known about the regional differences in the flow pattern. Positron emission tomography (PET) with [(15)O]H2O was used on eight healthy volunteers to assess regional cerebral blood flow (rCBF) during short-term exposure to hypoxia corresponding to simulated altitudes of 3,000 and 4,500 m. Scans at the simulated altitudes were preceded and followed by baseline scans at the altitude of Zurich (450 m, baseline-1 and baseline-2). Each altitude stage lasted 20 minutes. From baseline to 4,500 m, gCBF increased from 34.4 +/- 5.9 to 41.6 +/- 9.0 mL x minute(-1) x 100 g(-1) (mean +/- SD), whereas no significant change was noted at 3,000 m. During baseline-2 the flow values returned to those of baseline-1. Statistical parametric mapping identified the hypothalamus as the only region with excessively increased blood flow at 4,500 m (+32.8% +/- 21.9% relative to baseline-1). The corresponding value for the thalamus, the structure with the second largest increase, was 19.2% +/- 16.3%. Compared with the rest of the brain, an excessive increase of blood flow during acute exposure to hypoxia is found in the hypothalamus. The functional implications are at present unclear. Further studies of this finding should elucidate its meaning and especially focus on a potential association with the symptoms of acute mountain sickness.

Regional cerebral blood flow during acute hypoxia in individuals susceptible to acute mountain sickness

“…Berre (Berre et al 1999) demonstrated a 20-23% increase in middle cerebral artery velocity with hypoxia but found no significant difference between AMS-susceptible and AMS-resistant subjects. Using 15 O-H 2 O PET Buck (Buck et al 1998) reported no change in quantified global cerebral blood flow after acute (20 minute) exposure to 3,000 m, but a 36% increase (+7.2 ml/100g/ min) at 4,500 m (i.e. a greater hypoxic stimulus than the present study), although the blood flow was not compared with AMS symptoms.…”

Electrocortical and Hemodynamic Changes within the Brain during Incremental Bicycle Exercise in Normoxia and Hypoxia—A Combined EEG/NIRS Study

“…Special care was taken for the correct and secure fit of the sensors and double-sided adhesive tape underneath the probe holders was used to avoid sensor shift. For age dependent differences in the scattering medium of human tissue, differential path length factor was individually calculated based on participants age [26].…”

AltitudeOmics: The Basic Biology of Human Acclimatization to High Altitude. Addendum

“…Of note, , showed that acute hypoxia (ß15 min) increased VA, but not ICA, blood flow. Given that the areas perfused by the VA include the brainstem and posterior aspects of the thalamus and hypothalamus, increased blood flow and D O 2 to these regions during acute hypoxia (Buck et al 1998;Binks et al 2008) may be seen as necessary to maintain vital homeostatic functions Bilger & Nehlig, 1993). As increased cardiorespiratory drive with acclimatization was not associated with a continued elevation of VA D O 2 , we speculate that the increased VA D O 2 during acute hypoxia was protective, to defend against a potential threat to oxygen supply, rather than merely to support neuronal metabolic activity associated with heightened autonomic activity (i.e.…”