Cerebral Volumetric Changes Induced by Prolonged Hypoxic Exposure and Whole-Body Exercise

Abstract

The present study assessed the isolated and synergetic effects of hypoxic exposure and prolonged exercise on cerebral volume and subedema and symptoms of acute mountain sickness (AMS). Twelve healthy males performed three semirandomized blinded 11-hour sessions with (1) an inspiratory oxygen fraction (FiO 2 ) of 12% and 4-hour cycling, (2) FiO 2 = 21% and 4-hour cycling, and (3) FiO 2 = 8.5% to 12% at rest (matching arterial oxygen saturation measured during the first hypoxic session). Volumetric, apparent diffusion coefficient (ADC), and arterial spin labelling 3T magnetic resonance imaging sequences were performed after 30 minutes and 10 hours in each session. Thirty minutes of hypoxia at rest induced a significant increase in white-matter volume (+0.8 ± 1.0% compared with normoxia) that was exacerbated after 10 hours of hypoxia at rest (+1.5 ± 1.1%) or with cycling (+1.6 ± 1.1%). Total brain parenchyma volume increased significantly after 10 hours of hypoxia with cycling only (+1.3 ± 1.1%). Apparent diffusion coefficient was significantly reduced after 10 hours of hypoxia at rest or with cycling. No significant change in cerebral blood flow was observed. These results demonstrate changes in white-matter volume as early as after 30 minutes of hypoxia that worsen after 10 hours, probably due to cytotoxic edema. Exercise accentuates the effect of hypoxia by increasing total brain volume. These changes do not however correlate with AMS symptoms.

Vasogenic cerebral edema associated with the disability in activities of daily living in patients with chronic obstructive pulmonary disease

“…However, a previous study only calculated a decrease in FA on DTI maps in patients with COPD (Zhang et al., 2012b). Furthermore, previous studies have reported contradictory results, showing either increased or reduced ADC values in hypoxic brains (Rowland et al., 2017; Rupp et al., 2014). …”

Effect of exercise on night periodic breathing and loop gain during hypoxic confinement

“…Thus, the structural and functional cerebral alterations to combined stressors (hypoxia + exercise) may make breathing stability during sleep an even greater challenge. Since measurable brain volume changes can occur in as little as 6‐h in hypoxia, it is not a surprise there would be significant, measurable differences in dependent variables (e.g. AHI) between‐group in the current study, especially after a concomitant exposure of 2 × 60‐min moderate‐intensity cycling plus 14‐h continuous hypoxic exposure.…”

“…Ventilatory responses to exercise in hypoxia, in awake individuals, significantly increases the ‘period’ of periodic breathing experienced, and are positively related to both cardiac output and the ventilatory response to CO 2. Further, Rupp and colleagues have found that prolonged, moderate‐intensity hypoxic exercise can accentuate the acute effects of hypoxia, significantly increasing total brain volume, by up to ∼2%. Thus, the structural and functional cerebral alterations to combined stressors (hypoxia + exercise) may make breathing stability during sleep an even greater challenge.…”

The interactive effects of acute exercise and hypoxia on cognitive performance: A narrative review

“…Nevertheless, given that AMS symptom develops from several hours to 5 days following hypoxic exposure, AMS may contribute to cognitive impairment during prolonged exposure without acclimatization. Furthermore, exposure to hypoxia (hours to days) can lead to cerebral edema . Cerebral edema is the excess accumulation of fluid in the intracellular or extracellular regions of the brain, which is also known as brain swelling.…”