ISU Alumni Conference 2007 – Beijing, China – August 2007

Steve Ulrichand

Adam Rasheed

Space Life Sciences Department

International Space University

Adaptivity of the Vestibulo-Ocular Reflex to High Accelerations and Tumbling Motions

Motivation

Effects of micro and hyper g on vestibular system

• Balance problems

• Disorientation, visual illusions

Adaptation of vestibular system after multiple exposures?

Experiment Objective

• Characterize the adaptation of the vestibular system to high accelerations and tumbling motions

Presentation Outline

1. Motivation

2. Vestibulo-Ocular Reflex

3. Experimental Setup

4. Instrumentation

5. Results

6. Summary

Vestibulo-Ocular Reflex

The Vestibular System

Vestibulo-Ocular Reflex (VOR)

• Connects the labyrinth to the muscles which rotate the eyes

• Automatic control system that stabilizes the eyes

Otolith organs

Vestibulo-Ocular Reflex

VOR Gain

VOR Adaptation

• Measure of ability to track an object while your head is moving

• Evaluation of the VOR performance implies measurement of the VOR gain before and after exposure to the stimulus

Hypothesis

• After exposure, VOR gain will first decrease and then get better [Recovery]

• Repeated exposures over time will result in less degradation in VOR gain [Adaptation]

Vestibulo-Ocular Reflex

VOR Gain Measurement Techniques

• Classical Technique Drawback: Qualitative (not accurate)

• Video-Based Techniques Drawback: Specialized equipment is required (heavy and expensive)

• Gaze Deviation Technique (Watt et al., 1985) Advantage: Simple and relatively accurate

Source: Canada in Space, 1987

Vestibulo-Ocular Reflex

Gaze Deviation Technique

VOR GAIN = HEAD DEVIATION – GAZE DEVIATION

HEAD DEVIATION

Presentation Outline

1. Motivation

2. Vestibulo-Ocular Reflex

3. Experimental Setup

4. Instrumentation

5. Results

6. Summary

Experimental Setup

The Beijing High g and Tumbling Research Facility

• Description

vertical launch followed by tumbling motions

• Configuration

2 person spherical cockpit

• Height

120 feet

• Maximum Acceleration

5-6 g

• Duration

2 minutes

Experimental Setup

Video

Experimental Setup

ISU SSP 2007 Call for Bungee-o-nauts• Overwhelming response of 12 applicants

• Selection based on crew composition and compatibility

Experimental Setup

Crew Members

• International, intercultural and interdisplinary crew

Presentation Outline

1. Motivation

2. Vestibulo-Ocular Reflex

3. Experimental Setup

4. Instrumentation

5. Results

6. Summary

Instrumentation

Acceleration Measurement• 3-axis accelerometer

• video frame-by-frame analysis

Physiological Measurements• heart-rate monitor

• VOR-gain measurement

• Questionnaire

Video monitoring• on-board (crew response)

• vehicle tracking (handheld camera)

• launch camera (tripod 10 m away)

Instrumentation

Questionnaire

Presentation Outline

1. Motivation

2. Vestibulo-Ocular Reflex

3. Experimental Setup

4. Instrumentation

5. Results

6. Summary

Results

Acceleration• determined using frame-by-frame analysis

Results

Accelerometer• Data saturated at 2g

Results

Heart-rate monitor• Typical heart rate trace during one ride

0

20

40

60

80

100

120

140

Hea

rt R

ate

(bpm

)

Pre-Launch Peak Post-Launch

Results

Heart-rate monitor• Average heart rates during different phases of the test

Results

Questionnaire

• Major Symptoms Experienced Headache

Diziness

Sweating

Stomach Awareness

Shaking

• Other Symptoms Experienced Nausea when leaning forward

Floating head

High level of stress after the first ride

Increase in heart rhythm

Results

Questionnaire

• Time Recovery and Training Effect Sweating and shaking decreased after each ride

No effect on other symptoms

Sweating Shaking

Results

VOR Gain• Average of all subjects’ response

• Each point = average of 36 points

• Time recovery but no training adaptation

Results

VOR Gain• Individual responses

• Time recovery but no training adaptation

Time Recovery Training Effect

Presentation Outline

1. Motivation

2. Vestibulo-Ocular Reflex

3. Experimental Setup

4. Instrumentation

5. Results

6. Summary

Summary

VOR Gain

Symptoms

• Time recovery

• No clear adaptation (training effect)

• Major symptoms = sweating and shaking

• Time recovery

• Adaptation (training effect)

Acknowledgements

Thanks to Gilles Clément, Jeff Jones, Doug Hamilton, and Erin Tranfield for their valuable mentorship and support.

The authors also wish to gratefully acknowledge our Bungee-o-nauts: Bai Ding, Erin Tegnerud, Meritxell Vinas Tio, Ayako Ono for serving as test subjects for this experiment.

This work was supported by the Space Life Science Department of the International Space University is much appreciated.

Summary