High altitude sickness and the size of your brain?

Posted by David Cuthbert, MSIV, Drexel University College of Medicine

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Every year thousands of people flock to several world locations with one common goal in mind – to push their bodies well beyond what nature has so far intended by climbing to dangerously high altitudes.

For whatever reason this appeals to some people.  Those people are eager to overcome the restrictions set by Mother Nature, despite the obvious dangers.

As a kid I loved the move Cliffhanger with Sylvester Stallone.  I remember watching that film and thinking that the only real dangers associated with extreme altitude were obvious – falling (please see video clip # 1), Slyvester Stalone wanting to use you as a human sled (watch video clip #1 again), the cold, or John Lithgow going crazy and wanting to use a helicopter to kill you for money (please see video clip #2).

But apparently those aren’t the only dangers, and medical school has taught me some pretty interesting stuff.

In fact there are a whole variety of medical syndromes that can occur at high altitude that don’t involve John Lithgow, and being that this is a neurology blog, this piece will focus on the neurological high altitude medical syndromes.  And in particular, will place emphasis on one terribly interesting study.

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Elevated intracranial pressure at high altitude may be a function of brain size?

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The “Tight Fit Hypothesis”, and the story of one extremely curious neurosurgeon.

The neurological syndromes of high altitude sickness are thought to be a spectrum of illness ranging from high altitude headache (HAH), to acute mountain sickness (AMS), to the most severe – high altitude cerebral edema (HACE).

The exact pathophysiologic mechanisms leading to these conditions are still somewhat unclear but several theories have been proposed and tested – all of which related to hypoxia and elevated intracranial pressure (ICP).

It is thought that in the milder end of this spectrum (HAH) the symptoms are solely contributed from hypoxia, and as disease severity progresses, and the patient comes closer to HACE – the pathogenesis is more attributable to raised ICP.

But what I find even more interesting than just the development of these syndromes – is the fact that there is great variability between who develops them.  For some people, no matter how acclimatized they are they simply cannot go to a certain altitude without great risk of HACE and subsequent death.  While others require little acclimatization, and are capable to trekking to the summit of Mt. Everest without necessitating the use of supplemental oxygen.  This leads one to ask, what are the factors present that allow someone this ability to tolerate high altitude?

One answer (with considerable evidence to support it) lies within their genetics.  The discovery of a transcription factor called “Hypoxia Inducible Factor”, or HIF, confirmed this.  HIF is a transcription factor that contributes to the regulation of several metabolic pathways, and allows both production of a higher concentration of hemoglobin, and greater sensitivity of the carotid body to hypoxia.  Another older, and forgotten theory looks to further explain this increased altitude tolerance through anatomic differences.

In 1985 Ross suggested that the “random nature of cerebral mountain sickness” can be explained by “more compliant systems”.  In other words, if a person has larger sized ventricles, and/or more atrophic brain, they will in turn be less susceptible to altitude sickness because the compliance will leave them better equipped to tolerate the raise intracranial pressure.

Interestingly enough, there existed someone crazy enough to test this hypothesis.  Someone not only willing to hike to these ungodly altitudes, but also willing to screw a bolt in his head to measure his own intracranial pressure.  This person was Brian Cummings, an avid outdoorsman, who also just so happened to be a neurosurgeon.

Cummings and a team of ten undertook an expedition to the Kishtwar region of northern India to try to put this hypothesis to the test.  However the data obtained from the experiment was destroyed in a fire.  Or so everyone thought!  Then recently Cummings wife (Cummings has since passed away) found the data from the experiment, allowing it to have since be published.

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Mountain rage within Kishtwar region of northern India.

In this experiment the “tight fit” hypothesis was tested by using 10 subjects.  These subjects had computed tomographic scans of their brains to measure their ventricular size.  After which a scoring system was used to measure symptomatology related to high altitude neurological syndromes while at high altitudes.  Also, three lucky volunteers had their intracranial pressures measured – allowed via screwing a pressure monitor through a burr hole in their heads .  This stayed in place while trekking through Northern India Himalaya’s.  Cummings himself participated in the study, and also had a pressure monitor placed.

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Dr. Cummings manipulating ICP monitor

The results of the study showed that the three subjects with the smallest ventricles suffered the most from Acute Mountain Sickness, and reported the worst headaches of the group.  Meanwhile patients with larger to normal sized ventricles reportedly had significantly less clinical findings related to AMS:

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Regarding the intracranial pressure monitoring, of the 3 subjects to be observed, one had large ventricles, one with normal size, and one with small ventricles.  The only one to experience headache, was the patient with the highest observed rise in ICP, and was also the subject with the smallest ventricles.

Therefore the results of this experiment support Ross’s “tight fit” hypothesis, and provide a potential anatomic explanation to compliment other genetic mechanisms to explain why some people are more prone to developing high altitude neurologic syndromes.

Obviously, the small study size cannot definitively explain this susceptibility, nor can it exclude other mechanisms as contributing as well. Nevertheless this experiment is considerably important to those who wish to conquer the hypoxic environment of Mother Nature’s higher altitudes.

It allows an explanation for those that are less able to adapt, and maybe even one day provide a means of testing their ability to acclimatize prior to their summit attempt.  And while that very well may never happen, this study at the very least is a great story about the incredible strength of the human spirit.

Dr. Cummings showed incredibly determination while searching for answers regarding the human ability to adapt to their environment, and fortunately now his work can live on.

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Abraham Lincoln’s Ventriculostomy

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Ventriculostomy

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During ventriculostomy, the catheter is inserted through the brain and dura into the ventricular system via through a hole drilled into the skull.

Ventriculostomy, or external ventricular drainage, is surgical procedure to alleviate raised intracranial pressure by inserting a tube through the skull into the ventricles to remove cerebrospinal fluid.

Ventriculostomy was first used by Claude-Nicolas Le Cat for treatment of a newborn boy with hydrocephalus in 1744.

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Hydrocephalus before (A) and after (B) CSF drainage via ventriculostomy, showing significant reduction in ventricular size.

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Ventriculostomy for head trauma

Ventriculostomy is also used to measure (monitor) and treat raised intracranial pressure by draining CSF and blood to relieve increased pressure inside the skull from cerebral edema (brain swelling) after head trauma.

EVD trauma

Top row: CT scans after head trauma, showing bleeding and edema in the brain after head trauma, causing raised intracranial pressure.
Bottom row: Ventriculostomy (external ventricular drainage) used to monitor and treat raised intracranial pressure.

Untreated, raised intracranial pressure can result in “herniation” (downward compression of the brain stem), leading to dysfunction of vital centers that regulate breathing and heart function, and ultimately brain stem death.

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The Lincoln Assassination

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Lincoln was shot in the head by Johns Wilkes Booth at Ford’s Theatre in Washington DC on April 14, 1865.

The mortally wounded Lincoln was carried out of the theatre, across the street to the Petersen House , where he was attended by three doctors from the theater’s audience including army surgeon Charles Leale, later joined by other doctors including Joseph Barnes (Surgeon General Of the US Army).

Lincoln was declared dead at 7.22am on April 15, 1865.

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The Abraham Lincoln Head Shot

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Illustrations depicting Abraham Lincoln’s head wound by David A. Peace MS from University of Florida’s Department of Neurosurgery. The track of the bullet passes through the lateral horn of the lateral ventricle.

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The Doctor’s Notes

Dr Leale, feeling around by hand, discovered the bullet hole in the back of Lincoln’s  head right next to his left ear.  Leale attempted to remove the bullet, but the bullet was too deep in his head,and instead Leale dislodged a clot of blood in the wound. Consequently, Lincoln’s breathing improved.  Leale learned that if he continued to release more blood clots at a specific time, Lincoln would still breathe.

Here are some exerts from Leale’s actual account of the event:

I quickly passed the separated fingers of both hands through his 
blood matted hair to examine his head, and I discovered his mortal 
wound. The President had been shot in the back part of the head, 
behind the left ear. I easily removed the obstructing clot of blood 
from the wound, and this relieved the pressure on the brain.

As the symptoms indicated renewed brain compression, I again 
cleared the opening of clotted blood and pushed forward the button of 
bone, which acted as a valve, permitted an oozing of blood and re- 
lieved pressure on the brain. I again saw good results from this action.

The Hospital Steward arrived with the Nelaton probe and an ex- 
amination was made by the Surgeon General and myself, who introduced 
the probe to a distance of about two and a half inches, where it came 
in contact with a foreign substance, which lay across the track of the 
ball ; this was easily passed and the probe was introduced several inches 
further where it again touched a hard substance at first supposed to 
be the ball, but as the white porcelain bulb of the probe on its with- 
drawal did not indicate the mark of lead it was generally thought to 
be another piece of loose bone. The probe was introduced the second 
time and the ball was supposed to be distinctly felt. After this second 
exploration nothing further was done with the wound except to keep 
the opening free from coagula, which, if allowed to form and remain 
for a short time, produced signs of increased compression, the breathing 
becoming profoundly stertorous and intermittent, the pulse more feeble 
and irregular. After I had resigned my charge all that was profes- 
sionally done for the President was to repeat occasionally my original 
expedient of relieving the brain pressure by freeing the opening to the 
wound and to count the pulse and respirations. The President's posi- 
tion on the bed remained exactly as I had first placed him with the 
assistance of Dr. Taft and Dr. King.

lincoln death bed

It is clear that the bullet track left an opening into the lateral ventricle, a ventriculostomy.

When this ventriculostomy track occluded with blood clot and tissue, the dying President developed raised intracranial pressure, with compression of the breathing center in the brain stem and more labored breathing.

When the clot was removed, and the ventriculostomy opened, the President would transiently improve.

Lincoln’s ventriculostomy.