Normobaric hypoxia and symptoms of acute mountain sickness: Elevated brain volume and intracranial hypertension

Lawley, Justin S.; Alperin, Noam; Bagci, Ahmet; Lee, Sang H.; Mullins, Paul G.; Oliver, Samuel J.; Macdonald, Jamie

doi:10.1002/ana.24171

Cited by 50 publications

(59 citation statements)

References 30 publications

(44 reference statements)

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“…The measurement of ONSD seems to simply reflect a general rise in brain volume in subjects exposed to hypobaric hypoxia11. Despite that no direct comparison between brain volume, ICP and ONSD in hypobaric hypoxia has been made so far, a relative increase in ICP (although within the normal range) is suggested by the increase in grey and white matter volumes (and a decreased in CSF) after 10 and 22 h of normobaric hypoxia in MRI studies2930. The same effect on ICP was suggested by different in-field studies with other neuroimaging techniques11.…”

Section: Discussionmentioning

confidence: 99%

Oxidative stress response to acute hypobaric hypoxia and its association with indirect measurement of increased intracranial pressure: a field study

Strapazzon

Malacrida

Vezzoli

et al. 2016

Sci Rep

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High altitude is the most intriguing natural laboratory to study human physiological response to hypoxic conditions. In this study, we investigated changes in reactive oxygen species (ROS) and oxidative stress biomarkers during exposure to hypobaric hypoxia in 16 lowlanders. Moreover, we looked at the potential relationship between ROS related cellular damage and optic nerve sheath diameter (ONSD) as an indirect measurement of intracranial pressure. Baseline measurement of clinical signs and symptoms, biological samples and ultrasonography were assessed at 262 m and after passive ascent to 3830 m (9, 24 and 72 h). After 24 h the imbalance between ROS production (+141%) and scavenging (−41%) reflected an increase in oxidative stress related damage of 50–85%. ONSD concurrently increased, but regression analysis did not infer a causal relationship between oxidative stress biomarkers and changes in ONSD. These results provide new insight regarding ROS homeostasis and potential pathophysiological mechanisms of acute exposure to hypobaric hypoxia, plus other disease states associated with oxidative-stress damage as a result of tissue hypoxia.

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Section: Discussionmentioning

confidence: 99%

Oxidative stress response to acute hypobaric hypoxia and its association with indirect measurement of increased intracranial pressure: a field study

Strapazzon

Malacrida

Vezzoli

et al. 2016

Sci Rep

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“…16 Association between change in ICP and headaches was also recently reported in a study of acute mountain sickness, where severity of headaches was shown to be proportional to the hypoxia-induced increase in ICP as measured by MRICP. 17 …”

Section: Discussionmentioning

confidence: 99%

Imaging-Based Features of Headaches in Chiari Malformation Type I

et al. 2015

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Background Sub-occipital cough-induced headaches are considered a hallmark symptom of Chiari Malformation Type I (CMI). However, non-Valsalva–related suboccipital headaches and headaches in other locations are also common in CMI. The diagnostic significance and the underlying factors associated with these different headaches types are not well understood. Objective This imaging-based study compares cranial morphology and hydrodynamics in three types of headaches in CMI to better understand the pathophysiological basis for the different headache characteristics. Methods Twenty-two cranial physiologic and morphologic measures were obtained using specialized MRI scans from 63 symptomatic pretreated CMI patients, 40 with suboccipital-headaches induced by Valsalva maneuvers (34F, 36±10years), 15 with non-Valsalva related suboccipital-headaches (10F, 33±9years), 8 with non-suboccipital non-Valsalva induced headaches (8F, 39±13years), and 37 control subjects (24F, age 36±12years). Group differences were identified using two-tailed Student’s t-test. Results Posterior cranial fossa markers of CMI were similar among the three headache subtypes. However, the Valsalva-related suboccipital-headaches cohort demonstrated significantly lower intracranial compliance index than the non-Valsalva-related suboccipital-headaches cohort (7.5±3.4 vs. 10.9±4.9), lower intracranial volume change during the cardiac cycle (0.48±0.19 vs. 0.61±0.16mL), and higher MRICP (11.1±4.3 vs. 7.7±2.8mmHg, p=0.02). The Valsalva-related suboccipital-headaches cohort had smaller intracranial and lateral ventricles volumes compared to the healthy cohort. The non-Valsalva-related suboccipital-headaches cohort had reduced venous drainage through the jugular veins. Conclusion Valsalva-induced worsening of occipital-headaches appears related to a small intracranial volume rather than the smaller posterior cranial fossa. This explains the reduced intracranial compliance and corresponding higher pressure measured in CMI patients with headaches affected by Valsalva maneuvers.

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“…Total brain volume increased on average 59 ml involving mostly gray matter volume after 10 hours in hypoxia (Lawley et al, 2014). Intracranial pressure (ICP) was estimated non-invasively by an MRI method that had been validated in baboons and some humans.…”

Section: Mri Study Suggests Increased Brain Volume and Intracranial Pmentioning

confidence: 99%

Sightings edited by Erik Swenson and Peter Bärtsch

2014

High Altitude Medicine & Biology

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2014), the creator of these Sightings since the journal's inception, has many accomplishments in high altitude physiology and medicine, cardiorespiratory physiology, blood gas analysis and measurement by electrodes and spectroscopy (oximeters) and teaching, but also a long abiding interest and expertise in the history of medicine. In particular he has written numerous articles on the discovery of oxygen, which as historical research over the years has continued to uncover more claimants to the title of discover, which now must number six. In this brief and fascinating essay, he describes the work, lives, and times of these scientists who all should be rightly co-credited with the discovery of oxygen, whether or not they fully understood what they were observing. It is a story of insight, perseverance, technical prowess, and serendipity over several centuries even into our lifetimes, but also of intrigue, secrecy, religious controversy, and deception. Science can't get more interesting than this.Does Acetazolamide Limit Exercise Performance at High Altitude? Acetazolamide (Diamox) is effective in prevention of acute mountain sickness (AMS), but it may reduce exercise capacity. Roughly one half of studies have shown no impairment or even slightly better capacity, but others showed slight reductions despite better arterial oxygenation, either examining acetazolamide at sea level (with imposition of acute normobaric hypoxia) or after many days at high altitude in small numbers of subjects. Bradwell et al (2014) studied 20 middle-aged subjects one day after ascending to 3459 m by cable car. Subjects took prophylactic acetazolamide 250 mg twice a day (n = 10) for three days prior to ascent or placebo (n = 10) by the time they underwent a submaximal exercise endurance test (15 minutes at 60% of their sea level maximal oxygen consumption). Acetazolamide led to the expected 3-7% higher resting and exercise arterial oxygen saturations (SpO 2 ) and less AMS, although the fall in SpO 2 from rest with exercise was greater with acetazolamide (10% vs. 6%). One subject on placebo and four on acetazolamide failed to sustain 15 minutes of exercise and were the ones to show the greatest arterial desaturation. Increased ratings of perceived overall exertional effort (easy, medium hard, or hard) were statistically greater in those on acetazolamide, perhaps due to higher ventilation on the drug, although ventilation and blood gases were not measured. Whether the greater perception of exertional effort at higher levels of exercise relative to the exertion typical of trekking or vacationing at high altitude outweighs the benefits of acetazolamide in reducing AMS remain to be determined in larger studies examining such factors as age, drug dosing, exercise intensity and different altitudes and time at altitude.

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Normobaric hypoxia and symptoms of acute mountain sickness: Elevated brain volume and intracranial hypertension

Abstract: The data provide the strongest evidence to date to support the hypothesis that the "random" nature of AMS symptomology is explained by a variable intracranial pressure response to hypoxia.

Cited by 50 publications

References 30 publications

Oxidative stress response to acute hypobaric hypoxia and its association with indirect measurement of increased intracranial pressure: a field study

Oxidative stress response to acute hypobaric hypoxia and its association with indirect measurement of increased intracranial pressure: a field study

Imaging-Based Features of Headaches in Chiari Malformation Type I

Sightings edited by Erik Swenson and Peter Bärtsch

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