Unchanged Cerebral Blood Flow and Oxidative Metabolism after Acclimatization to High Altitude

Abstract

The authors investigated the effect of acclimatization to high altitude on cerebral blood flow and oxidative metabolism at rest and during exercise. Nine healthy, native sea-level residents were studied 3 weeks after arrival at Chacaltaya, Bolivia (5,260 m) and after reacclimatization to sea level. Global cerebral blood flow at rest and during exercise on a bicycle ergometer was measured by the Kety-Schmidt technique. Cerebral metabolic rates of oxygen, glucose, and lactate were calculated by the Fick principle. Cerebral function was assessed by a computer-based measurement of reaction time. At high altitude at rest, arterial carbon dioxide tension, oxygen saturation, and oxygen tension were significantly reduced, and arterial oxygen content was increased because of an increase in hemoglobin concentration. Global cerebral blood flow was similar in the four conditions. Cerebral oxygen delivery and cerebral metabolic rates of oxygen and glucose also remained unchanged, whereas cerebral metabolic rates of lactate increased slightly but nonsignificantly at high altitude during exercise compared with high altitude at rest. Reaction time was unchanged. The data indicate that cerebral blood flow and oxidative metabolism are unaltered after high-altitude acclimatization from sea level, despite marked changes in breathing and other organ functions.

Cerebral Formation of Free Radicals during Hypoxia Does Not Cause Structural Damage and is Associated with a Reduction in Mitochondrial PO2; Evidence of O2-Sensing in Humans?

“…The values obtained for CBF and CMRO 2 (and thus by consequence the derivation of L) were noticeably higher than those reported in previous studies using the same technique, although with 133 Xe as the tracer (Madsen et al, 1993;Moller et al, 2002). The reasons for this discrepancy are not clear, although we remain confident that they were not caused by the contamination of samples with blood from extracerebral regions or as a consequence of inadequate desaturation.…”

Effect of Hypoxia and Hyperoxia on Cerebral Blood Flow, Blood Oxygenation, and Oxidative Metabolism

“…A few other reports contradict our findings. Comparing high altitude (B11% FiO 2 ) to sea level, Moller et al, (2002) found no changes in CMRO 2 or CBF using a 133 Xe technique. Rockswold et al, (2010) studied O 2 metabolism in brain injury patients using a nitrous oxide technique and found that hyperoxia increased CMRO 2 , but Diringer et al, (2007) found no CMRO 2 changes.…”

“…Rockswold et al, (2010) studied O 2 metabolism in brain injury patients using a nitrous oxide technique and found that hyperoxia increased CMRO 2 , but Diringer et al, (2007) found no CMRO 2 changes. Several reasons may have contributed to these discrepancies, including different species, experimental conditions as well as pathological effects (Diringer et al, 2007;Maandag et al, 2007;Moller et al, 2002;Rockswold et al, 2010). Collectively, these factors make a direct comparison virtually impossible.…”

“…Collectively, these factors make a direct comparison virtually impossible. The techniques used in the previous studies required the injection of an exogenous tracer as well as continuous sampling of arterial and venous blood, all of which may present physiologic stress and alteration to the brain (Moller et al, 2002;Rockswold et al, 2010). The present study capitalized on a recently developed global CMRO 2 technique that was fast, reliable, and noninvasive (Xu et al, 2009).…”

The Contribution of Arterial Blood Gases in Cerebral Blood Flow Regulation and Fuel Utilization in Man at High Altitude

“…The majority of studies have reported unchanging cerebral metabolic rate of oxygen (CMRO 2 ) with severe (PaO 2~3 5 mm Hg) or moderate acute hypoxia at SL; 7 and after 3 weeks acclimatization to HA (5,260 m; PaO 2~5 1 mm Hg) in lowlanders 8 or in HA residents exposed to acute hypoxia at 3,800 m (PaO 2~4 1 mm Hg 9 ). Only one study has reported a 5% increase in CMRO 2 (using magnetic resonance imaging) during acute hypoxia roughly equivalent to 4,000 m HA (SaO 2 was not reported but was likely ~85%) 10 -this discrepancy likely reflects different methodologies and their respective assumptions.…”