neurovestibular/ocular physiologyneurovestibular physiology enae 697 - space human factors and life...

Neurovestibular Physiology ENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Neurovestibular/Ocular Physiology• Anatomy of the vestibular organs• Proprioception and Exteroception• Vestibular illusions• Space Motion Sickness• Artificial gravity issues• Eye issues in space flight

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© 2019 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu

http://spacecraft.ssl.umd.edu



Anatomy of the Ear

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From James T. Joyner, ed., NOAA Diving Manual, Best Publishing, 2001



Vestibular System

From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger, 1985

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Vestibular Sense Organs

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Sensing Roles of Vestibular Organs

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Semicircular Canal Responses

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Orientation of Semicircular Canals

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From Susanne E. Churchill, ed., Fundamentals of Space Life Sciences, Krieger Publishing, 1997



Ocular Nystagmus

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Otolith Responses

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Ocular Countertorsion

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Categories of Sensing• Proprioception (internal to body)

– “Self-Sensing”– Vestibular (inertial forces)– Muscle and tendon sensors (extension)– Joint sensors (angle)

• Exteroception (external to body)– Visual– Auditory– Cutaneous

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Thresholds of Rotational Perception• Rotational accelerations

– Yaw: 0.14 deg/sec2

– Roll and Pitch: 0.5 deg/sec2

• Mulder’s Constant– Acceleration x excitation time = 2 deg/sec– 5 deg/sec2 x 0.5 sec -> sensed– 10 deg/sec2 x 0.1 sec -> not sensed

• Rotational velocities - minimum perceived rotation rates 1-2 deg/sec (all axes)

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Transfer Function of Semicircular Canals

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Thresholds of Translational Perception• ax: 0.006 g• ay: 0.006 g• az: 0.01 g• Apparent change in direction of g vector = 1.5°

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Somatogyral Illusions

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Coriolis Illusion

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Somatogravic Illusion

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Inversion Illusion

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G-Excess Illusion

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Vestibular Adaptation to Space Flight• Otolith Tilt-Translation Reinterpretation (OTTR)

– Otolith signals are interpreted as translation rather than tilt

– Decays ~ 1 week post-flight

• Emphasis on visual and proprioceptive cues– Field dependent - orient in reference to nearby objects– Body oriented - assume world orientation is fixed by

body orientation– Inversion illusions

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Space Motion Sickness• “Space Adaptation Syndrome”• 2/3 of astronauts report some effects• Symptoms

– Primary: stomach discomfort, nausea, vomiting– Secondary: pallor, cold sweats, salivation, depressed

appetite, fatigue

• No correlation to susceptibility to motion sickness• Primary hypothesis: sensory conflict (Treisman’s

Theory)

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Progression of Space Motion Sickness

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SAS Experience of First 34 Shuttle Flights

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0

24

48

72

96

120

First Flight Subsequent FlightNone Mild Moderate Severe



SAS Experience of First 34 Shuttle Flights

24

0.00

0.25

0.50

0.75

1.00

First Flight % Subsequent Flight %

None Mild Moderate Severe



Space Motion Sickness Countermeasures• Preflight training

– Desensitization– Autogenic feedback training (AFT)

• Pharmaceuticals– Oral - scopolamine/dex-amphetamine (Scopdex)– Transdermal - scopolamine– Intramuscular - promethazine

• Mechanical systems– Pressurized insoles– Load suits– Neck restraints

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1

10

100

1000

10000

0 2 4 6

Rotation Rate (rpm)

Lunar gravityMars gravity0.5*Earth gravity0.75*Earth gravityEarth gravity

Artificial Gravity

€

grotation =ω 2r

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Allowable Rotation Rates• Select groups (highly trained, physically fit) can

become acclimated to 7 rpm• 95% of population can tolerate 3 rpm• Sensitive groups (elderly, young, pregnant women)

may have tolerance levels as low as 1 rpm

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Eye Issues in Space Flight• Early (Mercury/Gemini) astronauts reported

hyperacuity on orbit (resolution of cars/trucks/boats) - not verified in controlled conditions

• Recent results indicate some astronauts have noticeable visual degradation on long-term flights - may or may not return to pre-flight conditions post-flight

• Concern for long-term human exploration - lose ability to see well prior to Mars landing?

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VIIP Syndrome• VIIP=Visual Impairment Intracranial Pressure • Assumed to be due to fluid shift on-orbit

– Backs of eyes (w/ retina) moved forward towards lenses– Choroidal folds (“stretch marks”)– Inflamed optic nerves

• About 60% of long-duration crew notice some visual effects

• One crew went from 20/20 to 20/100 in six months - recovered to 20/50 post-flight

• Similar to idiopathic intracranial hypertension, papilledema (optic nerve swelling) on ground

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VIIP Diagnosis/Treatment• Need to monitor intracranial pressure

– Spinal tap – Direct measurement through skull– CT scans– Looking for flight-compatible bioinstrumentation

• Mitigation: reduce intracranial pressure/fluid shift– Lower body negative pressure– “Penguin” suits– Cerebral-spinal drainage– Pharmacological approaches?

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References• R. L. DeHart, ed., Fundamentals of Aerospace

Medicine, Second Edition Williams and Wilkins, 1996

• A. E. Nicogossian, C. L. Huntoon, and S. L. Pool, Space Physiology and Medicine, Third Edition Lea and Febiger, 1994

• A. E. Nicogossian, S. R. Mohler, O. G. Gazenko, and A. I. Grigoriev, eds., Space Biology and Medicine (Volume III, Book 1: Humans in Spaceflight) American Institute of Aeronautics and Astronautics, 1996

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