Neurologic Complications of Space Flight

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Space Sickness

Space (“motion”) sickness was an expected complication of space flight, that was the reason for all those crazy astronaut training machines:

However, the syndrome was unknown in the first manned space flights – none of the 26 astronauts who flew in the 16 Mercury and Gemini space trips experienced disorientation or motion sickness.

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However, this changed with the Apollo missions, where there were 11 incidents of inflight motion sickness, ranging from mild to severe, in as many flight missions.  This was attributed to the increased opportunity for movement by the crewmen within the relatively large volume of the combined Apollo command and lunar modules compared to the very confined crew compartments of the Mercury and Gemini spacecraft.

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The problem got even worse with Skylab, where 5 of 9 astronauts experienced symptoms of motion sickness during the initial days of the flight, 2of them severe including vomiting.

Anti-motion sickness drugs used by the Skylab 3 and 4 crewmen were not completely effective in ameliorating symptoms.

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Interestingly, these symptoms of motion sickness were temporary, and all resolved within a few days.

In fact, in-flight experiments conducted on or after day 8 showed that all crewmen had adapted to weightlessness, and did not experience any adverse symptoms in a spinning chair (30 rpm) sufficient to cause vertigo on Earth.

We have already blogged about how the vestibular system detects head movements.

Maintaining an awareness of the relative location of our body parts requires the precise integration of visual, vestibular, and proprioceptive (touch, pressure, and stretch receptors in our skin, muscles, and joints) sensory inputs.

If your head moves in space, your eyes see the movement, but in zero-gravity the vestibular otolith doesn’t move and there is no proprioceptive input from the feet against the floor.

Space sickness is felt to be the result of “sensory conflict” or sensory mismatch.

It didn’t occur in the early Mercury and Gemini flights, because the astronauts spent the whole flight strapped into a seat inside a small capsule with limited opportunity for movement and minimal exposure to conflicting visual, motor, and vestibular sensory messages.

However, space sickness has affected >50% of astronauts since Apollo, beginning within the first hour of transition from Earth gravity to microgravity, and persisting for 2 to 3 days.  It’s so predictable that no space walks were scheduled for the first 3-days of any Space Shuttle missions.

Recent research has suggested that virtual reality training can simulate specific effects of microgravity and may prove to be an effective countermeasure against space motion sickness through a process of habituation.

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Space Headache

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Space flights can also trigger headaches. In a 2009 study 71% of astronauts reported headaches – occurring during launch, flight, activities outside the space station and landing.  None had a history of recurrent headache on earth.  There was little to no association with the main symptoms of space motion sickness, such as nausea, vomiting or vertigo.

Asked to describe the headache, the astronauts mostly said the symptoms were “exploding” or “heavy feeling.”

We know that blood volume gets redistributed to the brain and upper body when the astronaut floats in zero gravity.

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This shift of blood towards the brain causes a painful increase in pressure within the skull:

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Click here to find out more.

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Correct clinical diagnosis of dizziness in the ER could save $$ billions

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We have already blogged about the danger of escalating health costs in the USA.

The cost of emergency room visits for severe dizziness has grown exponentially in recent years, topping $3.9 billion in 2011 and projected to reach $4.4 billion by 2015.

Investigators from Johns Hopkins estimate that half a billion a year could be saved immediately if emergency room physicians stopped the routine and excessive use of head CT scans to search for stroke in dizzy patients, and instead used simple bedside physical exams to identify the small group of patients that truly needs imaging.

Click here to find out more about the Johns Hopkins study.

Click here to find out more about the hidden dangers of unnecessary CT scans.

Once they understand how inner ear disease can cause vertigo and nystagmus, any physician can use our simple clinical scheme to distinguish inner ear problems from more serious and rarer central causes like stroke in dizzy patients.  Click here to find out how.

Benign Paroxysmal Positional Vertigo

Benign Paroxysmal Positional Vertigo (BPPV) is a common cause of dizziness, accounting for 1 in 5 of all cases of dizziness, and more than half of all cases of dizziness in the elderly.

Correct diagnosis is important, because this disorder can usually be easily corrected in a doctor’s office.

BPPV is caused by debris which has collected in in the inner ear, resulting in multiple recurrent short episodes of dizziness or vertigo, imbalance, and nausea provoked by specific head movements.

Because most cases of BPPV are from debris in the posterior semicircular canals, symptoms are generally provoked by rolling over in bed, looking  up (“top shelf vertigo”),  getting a hair wash, yoga positions etc.

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BPPV can be caused by head trauma, vestibular neuronitis, or posterior head positioning during dental work, hair washing or neck manipulation, but can also occur spontaneously.

The diagnosis of BPPV can be suggested by history, but is confirmed by a provocative test such as the Hallpike-Dix maneuver.   In this test, a person is brought from sitting to a supine position, with the head turned 45 degrees to one side and extended about 20 degrees backward. A positive Hallpike-Dix test consists of a self-limited episode of vertigo accompanied by abnormal eye movements (nystagmus) that comes on after a short latency period. The symptoms will often recur when the patient is brought back up to the sitting position, but after that will quickly fatigue.

The nystagmus can be made more obvious by removing visual fixation using Frenzel lenses:

Untreated, symptoms of BPPV can persist for a few weeks or months, then stop spontaneously, but will often come back again.  Affected patients will try to avoid provoking dizziness by sleeping with two or more pillows at night, not sleeping on the “bad” side, and modifying their daily activities so as to avoid head positions that exacerbate symptoms.

However, once correctly diagnosed, BPPV can be readily treated by simple maneuvers that can be performed in a doctor’s office, such as the Epley maneuver:

The Epley can be very effective, with an 80% cure rate, particularly when followed by the these precautions to reduce the chance that debris might fall back into the sensitive back part of the ear:
1. Have the patient sleep semi-recumbent for the next 2 nights in a recliner chair
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2. Encourage them to avoid tilting the head backwards for the next 2-3 days – do not go to the hairdresser or dentist, avoid putting the head back for shaving, accessing the top shelf or putting in contact lenses etc.  It is sometimes helpful to have the patient wear a soft cervical collar to remind them of this restriction.
3. If the symptoms recur when normal activity is resumed, the patient should undergo at least one further trial of the Epley maneuver.

If the patient cannot get to a doctor familiar with the Epley, they can try a home exercise such as the Brandt-Daroff exercises.  These exercises take longer to work, but many patients get significant relief of their symptoms within 7-10 days.

Download Brandt-Daroff Exercise Instructions Here

If the patient has persistent symptoms despite multiple attempts at the Epley and/or Brandt-Daroff exercise, one should first consider an alternate explanation for paroxysmal vertigo such as basilar migraine, acoustic neuroma, “Tournado” epilepsy or Meniere’s disease.  However, if the diagnosis of BPPV seems secure, and symptoms are truly recalcitrant, there are surgical options such as posterior canal plugging.